.

ENG INES FOR APower units that propelmodel boats ought to havea relevance to their craft,says Edgar T. Westbury.

S T E R N - W H E E L E R jIn this serial article hewill write about the kindof plant that is suitedto the famous river boats

WHEN steam power was first applied to marine navigationin the early years of last century, its possibilities and practicalproblems presented an inspiration and a challenge toengineers.

In the development of the steamship many ingeniousengines have been produced, including side-lever, oscillating,diagonal. and walking beam engines for driving paddlewheels; and direct-acting horizontal and vertical enginesfor driving propellers. Even at the present day, when thedesign of reciprocating marine engines has attained certainconventional features, they still offer a great deal of scopeto the model engineer. Although some tine models of marineengines have been exhibited at various times, they havemostly been isolated from their environment, and rarelyindeed have they been used to propel model steamships.

In view of the complexity of the modern marine engine,it would be difficult to build a true scale version that couldbe installed in a model of reasonable size. Most modelliners, if propelled by steam at all, have a simplified engineand boiler which is practical but not realistic. But modelsof small craft offer possibilities for engines which arerealistic in character, if not in detail. The primitive enginesof early steamships are relatively easy to build to scale in aconvenient size, but they have been sadly neglected, in com-parison with other “ period pieces,” such as locomotives orstationary engines.

The fact that the engines of ships are not usually visiblefrom outside may account for the lack of interest in makingmodels of them. Compared with the number of people whoare familiar with the working details of locomotives, veryfew have seen the inside of a ship’s engine room, and eventhose who have, cannot well appreciate the beauty anddignity of the machines in the small space available forviewing them. Those who claim to be shiplovers con-centrate their attention on external appearance, no matterwhether the vessel is driven by sail or power; and the former,being the more spectacular, generally has the advantage.Speaking for myself, all ships are beautiful, not only withskin-deep glamour, but in their innermost parts.

Up to the middle of the 19th century, steamships werealmost universally fitted with paddles for propulsion. Longafter the introduction of the screw propeller, many shipssuch as ferries, pleasure boats and harbour tugs were stillbuilt with paddles. With paddles there was a great advan-tage in manoevreing by driving the two wheels independ-ently, and this was probably the reason for their existence.In shallow or weed-infested waters, paddles had a still

longer lease of life, because they were less likely to becomefouled, and they were easier to clear if they did. One ofthe most popular and long enduring types of paddlesteamer was the “ stern-wheeler,” and it is with the objectof encouraging the modelling of this type of craft that thedesign illustrated has been prepared.

Some of the earliest experiments in the steam propulsionof ships involved the use of a single paddle wheel at thestern, including the abortive attempt by Jonathan Hulls in1736 the failure of which was the subject of muchsatirical comment from those who said “ it couldn’t be done.”

Hull’s boat had an “atmospheric” engine of the New-comen type, without a rotating crankshaft, and it drovethe paddle through ratchet wheels, ropes and counter-weights. One of the first successful steamboats, RobertFulton’s Clermont, (I 807) had a stern paddle wheel driventhrough gearing from a vertical-cylinder inverted-beam or“ side lever ” engine.

The development of stern and side wheeled paddlesteamers ran neck and neck for many years, but in thesmaller, shallow-draught vessels, the stern-wheel was pre-dominant. In the form which has been romanticised in

ROARIN' JENNY was built by Messrs Rawlings and Bray

MODEL ENGINEER I August 1965

story, song and film, its normal habitat was the MississippiRiver, where it was extremely popular for many years, notonly for passenger and freight carrying, but also as a mobilesaloon, music hall and gambling casino. Similar steamerswere used for river and lake transport in many other partsof the world, including Asia, Africa and central Europe,but the American ones were noted for their elaboratefurnishings, often rivalling those of a luxury hotel.

Many readers of the ME have expressed an interest inconstructing models of stern-wheelers, and a few interestingmodels have materialised, including the steam-driven Roarin’Jenny by Messrs Rawlings and Bray, of Southampton SME.This was elaborately equipped in the true Mississippi trad-ition; the more austere version by Mr E. J. Crossley ofLeicester SME was, I believe, electrically driven. Eithertype is satisfactory as a working model, and looks wellwhen under way. As free-running boats, they do not navi-gate as well as other kinds of craft, but they could easilybe adapted to radio control, which would eliminate thisdisadvantage.

I have often been asked for information on the designof engines suitable for model stern-wheelers, but authenticdetails are difficult to obtain. Some years ago I did someserious research in this matter, but though I made contactwith several people in America who had experience withthese vessels they were unable to furnish me with sufficienttechnical information. The available illustrations of thesteamers left a good deal to the imagination, as readers whohave tried to build models from the limited views shownin photographs or artists’s drawings will no doubt under-stand.

Spectacular typeThe earlier types of stern-wheeler were often fitted with

direct-acting engines driving cranks on either end of thepaddle shaft, and this is the type which is most likely tointerest model engineers, from the spectacular aspect. Latertypes had enclosed engine rooms, and drove the paddlesthrough chain and sprocket, or other gearing. Some modernstem-wheelers have had diesel engines with worm-gearedtransmission. These give plenty of scope for constructorswho are only interested in the propulsion unit as a meansto an end, but there must be readers who think that an enginewith its working parts on deck and fully visible has aspecial appeal.

It is a pity that the modern development of engineeringoften reduces or even destroys the attractiveness of machines.Working parts move too fast to allow their rhythm to beobserved, and mostly their high speed requires them to beenclosed for lubrication and protection. From the utilityaspect, there are. obvious disadvantages in slow-movingopen engines. In early stern-wheelers, engines often becamedamaged because of their vulnerable position; this mayexplain why they were usually brought head-on to thejetties (should I have said “ levees “?) instead of comingalongside.

I have devoted a good deal of space to the preamble be-cause I think that in introducing a special design, it is im-portant to explain the reason for its existence. To get downto the actual design, the set of engines shown is intendedto serve for a model of a steamer which in full size wouldbe about 120 ft long, with a 16 ft beam, and 6 ft 6 in. meandepth; draught when empty 19-3/4 in. aft and 4 in. forward.Such a boat would carry IO tons dead weight with a meandraught of 2 ft and 100 tons (maximum) with a draught of3 ft 6 in. The boiler, of locomotive type, would have about.

MODEL ENGINEER I August 1965

Mr E. J. Crossley, of Leicester, constructed thiselectrically-driven model of a stern-wheeler

400 sq. ft of heating surface, and work at a pressure of 150p.s.i.

I have not undertaken the design of a hull, as that is notmy speciality; but I consider that it should be scaled at 1/2 in.to the foot, that is, 5 ft long by 7-1/2 beam, and 3-1/4 in. depth.

Many kinds of marine engine cannot be rigidly stand-ardised, but have to be “ tailored” to fit the particularhull, or vice versa. In no case is this more evident than indirect-acting paddle engines, where the camber of the deck,either in plan or sheer, has an influence on the attitude ofthe engine and the immersion of the paddle wheel.

From illustrations examined, it appears that the hulldesign of stern-wheelers varied widely; some boats havean almost flat deck, others a concave sheer line, while ina few cases the stern “ tumbles home” to the extent ofnearly 10 deg. Similarly some hulls are almost parallel aft ofthe mid-line, while others taper sharply toward the stern.These factors must be taken into account, not only in theinstallation but often in the structural design of the engine.Obviously the immersion depth of the paddles must beunder control; in some cases it has been made adjustable, butthis introduces mechanical complication.

To cope with these varying requirements, some flexibilityin the basic design of the engine is essential. I consider itbest to avoid the use of castings for the main frames, infavour of fabricated construction; and such other castingsas are necessary are of a simple and straightforward nature,for easy production and machining. In many respects theconstructional work on the parts is similar to that on loco-motives, and therefore familiar to most ME readers; butother features are very different and call for special treat-ment.

The cylinders are 5/8 in. bore by 1-1/4 in. stroke, these pro-portions being conducive to high torque at low speed, anda typical feature of the stern-wheel engines is the long con-necting rod, the reach of which keeps the motion work wellclear of the paddle sweep. Often these rods were madeof wood, but in small size, this feature makes the attachmentof the little end and crankhead bearings rather difficult, andI have not followed it. To avoid excessive weight in these

Continued on page 573.

563

stood sentinel over the Antwerp of the sixteenth century,when long trains of packhorses lumbered in with silks andspices from Constantinople and furs from the Black Sea,luxuries to be exchanged for good cloth woven from thewool of English sheep. Even then Antwerp was a busyport : it is recorded that in 1569 five hundred ships enteredthe harbour in a single day.

To be continued.

WITTON LAKES Continued from page 559

went to Mr D. Bowman of Heaton with 0.1 error and thirdwent to Mr D. Shawcross of Tynemouth with 0.7 error.

After this competition there was a break for lunch, whenan unsuccessful attempt was made to run the hydroplanes.With temperamental engines and the water roughened by thewind, it was an occasion when nothing seemed to go right.Eventually it was decided to run it later in the afternoonto allow the steering competitions to start.

The course, a little over fifty yards, was the same asthat used for the nomination competition, and not surpris-ingly we had the same competitors. Unlike the course forthe radio control boats, which was exposed to the wind, thewater for the steering event was sheltered for about twothirds of its length by the high bank which separates the tworeservoirs.

It was the last part of the course which was disturbedby the wind and it was interesting to watch the effect onvarious boats, and to hear the excuses from the owners whentheir boats were well wide of the marker buoys !

Two craft in particular caused much amusement to theonlookers, but sheer frustration to their owners, Mr J.Lindstrom of Bradford and Charles Coleman of the St.Albans Club. On being released straight and true MrLindstrom’s boat decided that it liked the open water andso it turned at least go degrees to starboard. Pity to wastesuch a lovely day on running a mere fifty yards, seemedto be its attitude as it lifted its bow and headed away fromthe crowds. It was then a question of whether the enginewould run out of fuel before it reached the far bank.

The climax to these voluntary performances came toCharles Coleman’s launch. After a reasonable straight run,it was despatched on its return by one of the “ catchers.”It took a turn to port and headed out into open water again.Unfortunately for Charles his boat chose to test the hardnessof the bank and came off second best. With its bows splitwide open and its engine still roaring it made a gracefulimitation of a submarine as it vanished below the surface.

When it was salvaged and returned to is owner, a surveyof the damage proved that it would be running again in ashort time.

While these two boats were spending the afternoon in tripsround the lake, the remainder were engaged in the seriousbusiness of sailing for the target. The eventual winnerwas Mr P. Gladstone of Heaton. He was hard pressed byyoung Johnnie Blacknell who took second place and Mr D.Leach, also of Heaton, who came third.

This was my first visit to Witton Lakes and I was mostimpressed by the facilities. No doubt this venue will beseriously considered as a possible site when our Belgianfriends visit us next year. Having a love for the steamengine, I was more than pleased to see the entries from theNorth East. To those of you who share this interest, butwere absent at Witton Lakes, I would suggest that youmake a point of attending next year.

MODEL ENGINEER I August 1965

STERN-WHEELER

Continued from page 563

cumbersome rods, light alloy castings are specified for them.A set of marine engines cannot be considered really com-

plete without a fully operative reversing gear, though it istrue that in working model steamers, reversible engines arethe exception rather than the rule. It can rightly be arguedthat if boats are only run in the forward direction, re-versing gear is superfluous, but it certainly enhances realism,not only in the appearance of engines but also in facilityof control. If the reversing gear shown is thought to bean unnecessary complication, simpler alternatives, such asslip eccentrics, may be used, or the engines may be non-reversible by fixing the eccentrics. The conversion fromone form to the other entails no alteration to the generaldesign of the engine.

The frame design at first sight appears simple, but be-cause of the special conditions which have to be met-inmaintaining rigidity of structure and alignment of thepaddle shaft bearings-- it is not without a few practicalproblems. It is necessary to keep the engines as low aspossible, not only to obtain correct paddle immersion, butalso to obtain a low centre of gravity.

Paddle steamers of all kinds are liable to top-heaviness,especially stern-wheelers with elaborate superstructure. Theoverhang of the paddle shaft makes support at the afterend rather precarious, though it may be possible to extendside timbers of the hull, or provide oblique struts to giveadditional supports. Some boats have had further extensionof the timbers, with a cross beam aft of the paddles. Theframe structures may be regarded as cantilevers, cross-connected by a member under the slide bars, which maybe let in flush with the deck, or inclined to control the depthof paddle immersion.

Steel plate 1/8 in. thick, reinforced by 3/8 in. angle strips onboth sides, is used for fabrication of the frames. It isessential that the material be straight and true; the angulartruth of the angle strip should also be checked to ensure thatwhen attached, the strips present a flat face to make goodcontact with the cross member. The steel need not be bright-rolled; hot-rolled or black steel is in some respects better,as it is less liable to distortion, but it must be free frommill scale or rust.

Rolled angle section steel of the specified size may notreadily be obtainable, but larger angle steel may be cutdown to the required width, or folded angle strips may beused. For preliminary operations, the strips may be tem-porarily attached by screws or bolts, until other parts havebeen located and fitted. When finally riveted, the headsshould be filed flush, or at least project as little as possible,so that they cannot interfere with the fitting of the otherparts. The aperture for fitting the cylinder, and the holesfor bolting it in position, are obviously related to the matingparts. Do not forget that the frames and certain other parts,are in pairs, and mirror-inverted to each other.

The cross member is simply a flat steel plate, sufficientlywide to brace the complete engine structure and attached tothe frame angles by countersunk screws from the underside.Its width cannot be definitely fixed as it must be related tothe beam of the hull at the particular point and the overhang(if any) of the engine cylinders.

(To be continued)

573

4

WEIGH SHAFT

- - - - - - -_ _ _

SLIDE VALVE AT MID TRAVELCROSS MEMBER

GENERAL ARRANGEMENT ENGINES FOR STERN WHEELER

561

m m

------___ - ---__

ERSING LINK

ECCENTRICS AT FULL STROKE

A H E A D \ _ 4

ASI

1-_-----

-I -

RL PORT ENGINE ONLY SHOWN

562

8”

M A I N F R A M E I OFF EAt

I22/---4 I

l/,111_ 9/&j- 9,/p&- 9,++--

9/64" DIA. C’SUNK ON UNDERSIDE

L E N G T H T O SUIT BEAM OF HULL

/TAP 6 B.A.

CROSS MEMBER I OFF M.S. 2 OFF M.S. VA LV

564 MODEL ENGINEER I August 1965

TAP 4 B.A. 7/64" HOLESL O C A T E FROM

NOTCHED TO FIT RIVETS SPACED 9/16" APART MAIN BEARING

O F F E A C H R.H. & L.H.

SECTION AA

TAPPED FORS, ,,LUJR I CATOR/B 9 \

BRONZE- -

VALVE ROD GUIDE 2 OFF BRONZE MAIN BEARING I OFF EACH R.H. & L.H.

MODEL ENGINEER I August 1965 565

ENGINES FOR A STERN-WHEELER

Continued from August I

IN a hull of 7-1/2 in. beam, the crossmember may be 6 to 6-1/2 in., but ob-viously it must be fitted so that theframes are exactly parallel with eachother to allow the main bearings to belined up with each other. The crossmember may be used as a platform formounting the control gear, includingsupports for the weighshaft, betweenthe port and starboard engines. It ispermissible to substitute two narrowstrips for the wide cross member, butthey must be braced by diagonal strutsor otherwise prevented from shiftingout of square with the frames.

The longer of the two angle stripsattached to each of the frames has agap cut in its horizontal and verticalfaces to fit the slide-bar bracket. Asits position must be located in relationto the cylinder axis, to ensure truealignment of the slide-bars, thebracket’s dimensions and fixing holesmay be subject to slight modification,so it is best not to fix them at thepresent stage.

~Slide bracketsThe simplest way to make the slide

brackets is to cut rectangular pieces offlat steel bar or sheet, I0 in. wide X1-1/4 in. long, with allowance for any ex-ternal trimming which may be neces-sary. A hole 7/8 in. dia. is drilled andbored in the centre of each piece, andthe two pieces may then be clampedor soft-soldered together for furtheroperations. Some fitting on the seat-ings for the slide-bars will be necessarywhen lining up the parts to compen-sate not only for any possible errors intheir dimensions, but also for thethickness of any packing used in thejoints of the cylinder assembly.

For the same reason, the distancebetween the seating faces and the boresof the valve-rod guides cannot be pos-itively determined. They can be drilledand reamed, and the faces milled orfiled parallel to the bores, but it isadvisable to leave something on themfor final fitting. Fixing holes in theguides and the slide-brackets shouldalso be left until the various parts canbe assembled and lined up.

The main bearings can best be madefrom bronze or gunmetal castings.Although it is not necessary that theyshould be split, it will facilitate assem-

594

bly and alignment, besides being inconformity with good practice, if theyare made as shown in the drawings.

There must be an allowance for cut-ting and facing if the caps are cast inone with the lower part, and it is bestto drill and tap the holes for the fixingstuds before cutting. After facing thejoint surfaces and securing the capswith temporary screws, the castingsmay be mounted either in the four-jaw chuck or on the faceplate for boringand facing on one side; the reverseside of the bore can be faced by clamp-ing the bearing on a mandrel.

At this setting, a facing cut can alsobe taken over the mounting flange ofthe bearing, as far as possible withoutfouling the corners, to serve as a wit-ness when milling or filing this face,which must obviously be exactly squarewith the bearing axis. The shoulderof the flange should bed firmly againstthe edge of the frameplate.

Either bolts or setscrews may beused to attach the bearings to theframes; with bolts, the holes in bothparts should be a close fit for 6 BA, toserve as dowels and prevent any side

by Edgar T. Westbury

movement. With the bearings mountedon the frameplates, and these held intheir correct relative positions byassembling the cross member, the align-ment of the bearings should now bechecked by fitting a 5/16 in. test barthrough both of them. To correcterrors, the faces of the bearing flangesmay be filed or scraped as required,but this should not be necessary unlessthey have been incorrectly machined,or the frame plates are out of truth.

Main frameWhen properly aligned, the test barshould pass freely through both bear-ings and make contact over the fulllength of their bores.

The cylinder group of componentshave a general resemblance to thoseused in locomotive practice, and mostME readers will be familiar with themethods of machining and fittingthem. To constructors who have no

TAP 6 B.A. LOCATE HOLES FROM STEAM CHEST

II-

I-‘I

5 k- LOCATE FROM COVERSAT BOTH ENDS

T CYLINDER

?B” 2 OFF BRONZE

A30”

3

\2 HOLES 3/32" DIA.

EACH END

MODEL ENGINEER 15 August 1965

previous experience with this work, itmay be explained that the cylinder,steam chest and covers are generallymade from bronze or gunmetal cast-ings, though they can be machinedfrom solid metal, or fabricated, if thisis more convenient.

The cylinder can be held in the four-jaw chuck for boring, and for facingthe flange at one end. A smooth andparallel bore is most essential, and al-though minor errors in both respectscan be corrected by lapping-prefer-ably at a later stage of operations-itis sound policy to produce as good atool finish as possible in the first place.The flange face which, when fitted,will be adjacent to the piston rodgland, must be exactly square with

and cylinder constructionthe cylinder axis, so it should be mach-ined at the same setting as the boringoperation. At the other end, accuracyof the flange face is somewhat less im-portant, so it may be machined eitherby reversing the casting in the chuckand bedding the finished flange facefirmly against the chuck face, or bymounting on a mandrel. Identificationmarks should be made to show relativeassembly positions of mating parts.

Port faceTo machine the port face truly par-

allel with the cylinder axis, the mostconvenient method is to mount thecomponent on an angleplate, using asingle bolt through the bore and aplate or disc to bear on the flange. Themachined surfaces should be protectedfrom burring or bruising by inter-posing tough paper. After setting upthe angleplate on the lathe, so that theport face is fairly central, and offsetweight has been balanced by attachingodd pieces of metal to the faceplate, theport face can be machined flat andtrue. The distance of the face fromthe cylinder axis should be exactly1/2 in.

It is necessary to produce a truesurface on the rebated joint face whichsurrounds the port face. There areseveral ways of doing this includingmilling, shaping, or hand filing, but ifa rotary-spindle milling attachmentwith a vertical slide is available, it is avery simple matter to end-mill it whilethe work is still set up for dealing withthe port face. The lathe mandrel

MODEL ENGINEER 15 August 1965

should be locked with the cylinderaxis horizontal; this can be done some-times by engaging the back gear, buta more positive method is to tie thefaceplate, by a bar or bracket engagingwith the channel of the lathe bed orother stationary part. The cylindermust be prevented from any movementwhile milling the four sides of therebate, and the depth of cut must bethe same all round to produce a flatsurface.

An alternative method is to mountthe cylinder on a vertical slide, withthe port face square with the latheaxis, and use an end mill running inthe lathe chuck. In either case the re-bate should be 3/16 in. back from theport face, and the projecting rectangle

/-

not important so long as the requiredport area is obtained. The method isgenerally considered satisfactory, givencare and patience, for it allows ports

of ample depth to be produced, but thelimited speed of most lathes is notsuited to running small cutters at theirbest efficiency. A method of side mil-ling, by using cutters of small diameteron shanks of minimum permissiblesize, has been described in some of myarticles on steam engines. It producesports of high accuracy, but limiteddepth, and dispenses with the need fora vertical slide. A full description ofthe various methods of port cuttingcan be found in the PM handbookMilling in the Lathe.

Some of the older craftsmen, in thedays when machine tool facilities werepractically non-existent, producedports by drilling a row of holes andjoining them up with a small cross-cutchisel, but such methods are unneces-

A 6 HOLES

CYLINDER COVERS 2 OFF EACH BRONZE

of the latter should measure 5/8 in. X1-1/4 in. This fits the aperture in themain frame, and the port face projects1/16 in. on the other side, less the thick-ness of any jointing material usedbetween the surfaces.

Methods of cutting ports in cyl-inders have always been the subject ofdiscussion. The most popular methodis by end milling, with the cylindermounted on a vertical slide and thecutter running in the lathe chuck.This produces round-ended ports in-stead of the square-ended ports asshown in the drawings, though this is

sarily tedious nowadays. Again, skilledmoulders in the old days could pro-duce castings with ports and passagesaccurately cored in, but this is notnow considered practicable except incylinders of comparatively large size.But whatever method is employed, theimportant thing is that the ports shouldbe in the right place and cleanly cutso that they can be properly controlledby the slide-valve.

A rather unusual feature of the cyl-inder ports is that the central port,which leads to the exhaust outlet, is

Continued on page 608

595

Tapped to take Allenscrew and washer

Taper to suit ’lathe mandrel

Close fit for boreof wheel

FIG.2 LOCATING SPIGOT FOR WHEELTURNING

desired hole in

FIG3 CRANKPIN DRILLING JIGSilver steel or M S case hardened

silver steel for locomotive axles.Ground mild steel is the stuff we want,and it is generally obtainable in sizessuitable for scales up to I in. Abovethis size, axles will probably have to beturned between centres anyway, but ifthey are not, proper centres should al-ways be put in, if only for their real-istic appearance. A final small point-axle wheel seats should be made a fewthou longer than the thickness of thewheel at its boss; thus after pressinghome, the axle will protrude veryslightly.

Toolmakers clamp

FIG 4 CRANKPIN DRILLING JIG IN USE

articulated suburban stock, Atlantics,Pacifies and occasionally a GC enginestormed or coasted by (depending onits direction) with an express. And, ofcourse, there were the three-cylinder

. Moguls, on the fast goods. Now thepath is closed, and diesel has replacedsteam.

But to get back to wheel coning, asmodel tracks do not normally botherto cant their rails, the coning of thewheels is hardly worth while.

Bogie, trailing and tender wheelswill now be ready for their axles, butdriving and coupled wheels must havetheir crankpins fitted before proceed-

ing further with the assembly.Small diameter axles may be turned

in collets, but the three-jaw can beused. If it is insufficiently accurate,the old dodge of packing out theoffending jaw or jaws with strips ofpaper can be tried. This is wherethe d.t.i. comes in so useful. The axlemust be running really true before anattempt is made to turn the wheel seat.Some workers get by with a piece ofwhite chalk; others make trial cuts withthe tip of a lathe tool (a knife tool isthe one to use here) but give me ad.t.i. every time!

A simple jig must be made up fordrilling the driving and coupled wheelsfor their crankpins. My sketch showsa suitable one, and you will noticethat it is made long enough to enablethe builder to clamp it to the wheel.It is shaped so that it can be locatedfair and square with the crank boss.When clamping, care must be taken toprevent the jig from being tilted.

There is, incidentally no need to use To be continued.

ENGINES FOR A S T E R N - W H E E L E R Continued_from page 5 9 5

in the form of a round hole instead ofrectangular. It has always struck meas rather strange that most designersshould insist on orthodox practice inthe shape of this port, since it playsno essential function in the scheme ofvalve events and is not opened andclosed by the slide-valve. Thereforeit does not matter what shape thisport is, neither need its location beprecise, so long as it is large enoughto give adequate passage to exhaust.

It may be mentioned that all the portand passage areas of this cylinder arewell on the large side for the slow

608

speed at which the engines are intendedto be run. Despite the many argumentswhich have been put up in favour oflarge ports, I have found by exper-ience that they are not invariablyessential to efficiency. But they facili-tate control of valve events and giverapid opening and closing, which is allto the good. Wiredrawing of steamis not always an evil, and may some-times be used to advantage; but itshould not occur in the cylinder ports.

The passages from the ends of thecylinder to the ports are in the formof holes drilled at an angle of 30 deg.

to the cylinder axis. To start the drillaccurately, a local chamfer should bemilled or filed in the mouth of thecylinder at an angle approximately per-pendicular to that of the passages. Asimple method of ensuring that theholes are drilled at the correct angle isto make a hardwood or metal blockwith a flat base, and a top surface at30 deg., equipped with a long stud orsetscrew for securing the cylinder inposition. A small centre-drill maywith advantage be used for starting theholes, as it is far less liable to wanderfrom the correct position than the re-latively flexible twist drill.

To be continued.

MODEL ENGINEER I5 August 1965

ENGINES FOR A STERN-WHEELER

Continued from August I

Machining the working partsIT may be observed that the circularport of the cylinder contour is 1/16 in.less in diameter than the flanges of theend covers, which they might normallybe expected to match. The reason forthis is that the recessed parts of thecylinders are intended to be laggedwith insulating material, and coveredwith either wood or metal cleadingfitted flush with the edges of thecovers.

The cylinder covers have registerspigots which should fit closely in theends of the cylinders, though this isimportant only in the ends whichcarry the piston rod glands. For theother end covers, the spigot, joint faceand inner face may be machined at onesetting by gripping over the edge ofthe flange in the chuck. The reverseside may be rough faced by holding inthe same way, but to fiinish the faceand also to turn the edge of the flange,it should be gripped over the narrowsurface of the spigot, with the flangebedded against the chuck jaws. Some-what different procedure is called forwith the covers at the gland end tomake certain that the register and thegland recess are exactly true with eachother. If the inner side is machinedfirst and the hole drilled for the pistonrod, it may not be easy to ensure thatthe counterbored gland recess is trulyconcentric when the cover is reversed.

My favourite method is to firstchuck the cover with the gland bossoutwards, and to face, drill and counter-bore the hole as truly as possible. Astub mandrel is then machined in thechuck, with a pilot extension to fit thesmall hole, and the cover mounted onit for machining the inner face andspigot. In this way the truth of theessential surfaces is positively assured,even if a slight error should occur indrilling and counterboring.

Incidentally, some constructors finddifficulty in turning register spigots toa snug fit. The job will be simplifiedif the spigot is first made with extralength allowance, and when nearingfinished size, trial cuts are taken onlyon the extreme end. If this part shouldaccidentally be turned undersize, therest of the spigot may still be made a

MODEL ENGINEER I September 1965

3/1: DIA.

CYL . GLAND

2 O F F BRONZE

little larger to fit properly; the excesslength of spigot is then faced back tothe finished length.

The top and bottom faces of thegland boss to the cover will need to bemachined or filed exactly parallel withthe axis, and at the same distance fromit. This is another operation where theuse of a milling attachment will help toensure accuracy. The same applies tothe drilling of holes in the flanges ofboth pairs of covers. Note that theholes above and below the gland bosseshave to be countersunk; screws withprojecting heads cannot be fitted inthese positions, because the ends ofthe slide-bars have to be butted closelyagainst the flange face.

Little need be said about the mach-ining of the gland, as the essentialturning and drilling operations can becarried out at one setting by grippingthe flange in the four-jaw chuck. Itshould be an easy working fit on thepiston, and also in the counterbore ofthe cover. The three-jaw chuck canbe used to hold it in the reverse po-sition for facing the top of the flange.After drilling the stud holes, the flangemay be used as a jig to locate the tap-ping holes in the cover boss. In thesame way, the covers may be used forjigging the holes in the cylinder. Theangular position of the flats on thegland boss of the cover is important;it may be located by laying the cylinderbv its port face on a surface plate and,with the cover in position, checking

by Edgar T. Westbury

the angle of the flats on both sides witha try-square.

Note that front and back covers havethe spigot chamfered or bevelled loc-ally to avoid restricting the openingfrom the drilled steam passages intothe cylinder. The position of thechamfer can be located from that onthe mouth of the cylinder bore, andeither milled or filed at approximately30 deg. to the spigot face.

The steam chest is of a type familiarto steam engine builders, and is bestmade as a casting with a rectangularaperture, which will need to be filedto fit over the port face projection ofthe cylinder. For machining the twoside faces, the casting may be held inthe four-jaw chuck, and after the firstfacing operation, it should be reversedand bedded firmly against the chuckjaws, so that parallel accuracy of thetwo sides is assured.

To drill and counterbore the glandrecess, the casting may be mounted onan angle plate by one or more boltsthrough the aperture, and set up onthe faceplate with the boss runningtruly. It should be noted that the bossis not symmetrical with the two sidefaces, but is offset towards the outsideface. After concentric drilling, counter-boring and tapping of the boss, itsexternal diameter and the end face maybe skimmed at the same setting to pro-duce a clean finish.

A piloted stub mandrel should thenbe turned in the chuck, and threaded tofit the gland recess, so that the castingcan be mounted for drilling and tap-ping the reverse end exactly in line.After centre-drilling, but before dril-ling the hole, the tailstock centre maybe used to support the work whilefacing the end surface. With due carein these operations, the valve rod, whenfitted in the gland and tail guide, willslide freely and in true parallel align-ment with the cylinder axis.

The steam chest cover casting issimply a flat plate with the centre re-lieved to form a recessed panel, witha raised flange face to match the steampipe joint. If desired, it may be modi-fied, by tapping the centre hole, totake a union or other pipe fitting. It

649

%‘HOLES 1/8" HOLES, LOCATE FROM STEAM CHEST I_

BOTH ENDS

STEAM CHEST 2 OFF BRONZE

is also permissible to fit the steamsupply pipe to the top face of the steamchest, if this position is more con-venient, but care should be taken toavoid the fixing studs. Generallyspeaking, the flange joint on the coverwill be found the neatest and mostpractical fitting. In any case, the covermust be faced truly flat on the innerside, and then reversed for facing theflange and the outer rectangle as truly

STEAM CHEST COVER __2 OFF BRONZE

parallel as possible. The inner coverface, and both sides of the steamchest, may be lapped to produce trueflat joint surfaces.

The fixing holes for these two partsshould first be drilled in the steamchest, which is then used as a jig tospot the holes in the cover. Take careto identify the mating parts in relationto each other, by punch marks or figurestamps, so that they can be located the

- B.A.

DIA.

VALVE ROD GUIDE 2 0 F F B R A S S- - V A L V E R O D G L A N D 2 O F F B R A S S

DIAPISTON ROD 2 OFF STAINLESS S.

PISTON 2 O F F- - C.I

650

same way on final assembly. The cyl-inder should now be fitted to theaperture in the mainframe, the steamchest fitted in place, and clamps usedto hold the parts in place while spot-ting the clearance holes in the frame-plate and the tapping holes in the cyl-inder.

As it is necessary that the final loc-ation of the group of parts should befixed for lining up other working parts,they should be assembled with the nec-essary jointing material between thesurfaces on both sides of the frame-plate. It should not be necessary to usethick packings, if machining has beencarried out correctly. I find that toughbrown paper, like that used for wrap-ping, is satisfactory for steam joints upto fairly high temperature; on finalassembly, it should be coated on bothsides with Wellseal or other jointingcompound. The thickness of the paper,when under compression, will be about4 to 5 thou, which must be allowedfor when lining up both the crossheadslide-bars and valve-rod guide.

The piston should preferably beturned from a piece of cast iron, butif this is not available, hard bronze orstainless steel may be used. It is mach-ined all over, and if the centre hole andthe external glands are turned at onesetting, their essential accuracy isassured. There are several ways ofattaching the piston to its rod, all ofwhich are satisfactory if properly car-ried out, but I have found that fittingthe end of the rod closely to a parallelhole and securing it with a nut, is asgood a method as any. Of course, itinvolves turning the rod down accur-ately, either in a good collet chuck orsetting it up in the four-jaw chuck withthe aid of a dial test indicator, but the

MODEL ENGINEER I September 1965

VALV

STNLS S.~ 3/32

SLIDE VALVE

2 OFF C.I.

trouble involved is well worthwhile.In some cases it may be considered

best to leave the lands of the pistonslightly oversize and finish them afterfitting to the rod, but this is of no ad-vantage unless the rod is set up to runtruly while the operation is carriedout. The piston should be fitted toslide smoothly in the cylinder bore. Itsgroove is packed with graphite impreg-nated asbestos yarn to produce a resil-ient but not excessively tight seal.Similar packing material is used forthe piston and valve-rod glands, whichshould be well filled and compresseddown, but not screwed up tighter thanis necessary to prevent leakage whenworking.

The valve-rod tail guide and glandmay be made from brass, and careshould be taken to ensure that thethreads are concentric with the bore ineach case. Tommy-bar holes in thegland, as shown, will be found mostconvenient for running adjustment, buta hexagonal head, and a slightly domedblind end, is more appropriate for thetail guide. The length of the pistonrod may be subject to slight modifi-cation on assembly.

It is possible to machine the cross-head from solid or from a casting, butthe fabricated construction shown willbe found simplest, as it avoids the needfor milling or recessing operationswhich some constructions may finddifficult. Mild steel, casehardened be-fore final assembly, is recommended,but hard bronze may be used as analternative. The centre piece shouldbe made of a thickness to match thewidth of the slide-bars, and the verticalheight should be the same as the dis-tance between flats on the boss of thecylinder cover. This dimension may

MODEL ENGINEER I September 1965

be left slightly oversize until the axialhole has been drilled and tapped, whenit may be screwed on the piston rod,and with the piston and its rod as-sembled in the cylinder, the crossheadis lined up from the flats and its topand bottom faces machined or filed tothe correct levels.

A crosshole is drilled through thecentre of the piece, to take a bolt whichwill clamp the two side cheeks in placewhile drilling the four holes for therivets through all three pieces. Theyare now separated, the crossholethrough the centre part is opened outto 3/8 in. dia. and then sawn out to formthe mouth, which must clear the swingof the connecting rod.

Though there is no objection tousing rivets with projecting heads forjoining the parts together, flush rivetswill generally be preferred, and I in.wire nails in fairly close-fitting holescan be used in the absence of moresuitable soft iron rivets. A worthwhiletip in flush riveting, when it is desiredto make the rivets invisible, is to taperthe holes in the outer plates instead ofcountersinking them. A broach or D-bit with an angle of not more thanIO deg. inclusive, may be used for thispurpose. This avoids the wire-edgedflash formed when rivets are closedinto an obtuse-angle countersink, andwhich often shows up when they arefiled flush with the main surface. Fin-ally, a countersunk hole is drilledthrough the top of the crosshead, sothat some of the oil which is scrapedoff the slide-bars can be collected andfed to the little end bearing of theconnecting rod.

The valve rod is made from 1/8 in.stainless steel, which must be set upto run truly for screwing the end witha tailstock die, and in the reversedposition for reducing the diameter to3/32 in. for a length of 1/4 in. This por-tion engages the slot in the back of theslide-valve and provides the means ofmoving it, without imposing any re-straint on its ability to seat itselfproperly. A slot across the end of therod will allow the valve to be finelyadjusted for position, with a screw-driver, if the tail guide is removed.There are several alternative methodsof coupling the rod to the valve, butthis is one of the simplest which givesthe required results.

Slide-valves for small engines areusually made of bronze or gunmetal,but I have always considered these un-suitable for working on a cylinder portface of the same or similar metal. Itschief merit appears to be that it is

relatively easy to cast accurately toshape, though many slide-valve castingsI have come across have been far fromclean and accurate. I have made slide-valves of cast iron for several engines,and I find that they have much betterwearing properties, especially whenlubrication is meagre or infrequent, andthey retain steam-tightness muchlonger than bronze.

It is possible to make slide-valvesfrom solid without any great difficulty.My method is to take a piece of metalrod or solid cast stick, large enoughto clean up to the diagonal size of thevalve (in this case 15/16 in. dia.) andlong enough to hold in the chuck withabout 1/2 in. projecting. This is facedflat on the end and recessed 3/8 in. dia.for a depth of 1/16 in. with a flat endeddrill or end mill. The back of thevalve is then necked down to about3/8 in. dia., leaving a disc 1/8 in. thick.Before parting the valve from the stockrod, most of the shaping, both on theoutside edges and the rectangular re-cess, can be carried out. The use of arotary-spindle milling attachment ona vertical slide, with the work still setup and the lathe mandrel locked in afixed position, will simplify these oper-ations. A very small end mill or dentalcutter must be used to square out thefour sides of the recess; even so, itwill leave a slight radius in the corners,but this will not matter so long as itdoes not restrict the opening area ofthe ports to any great extent.

Greater skill and patience is neces-sary to shape the valve by handmethods; it is not difficult to file theoutside edges, including the bevel (theobject of which is simply to eliminatesurplus metal), but the recess can onlybe squared with the aid of a smallchisel if end milling facilities are notavailable. After parting off the valve,the projecting boss is milled or filed toshape, and a slot cut in it to take thereduced portion of the valve rod aclose, but not tight fit, with no endplay. The face of the valve shouldfinally be lapped to exact flatness andsmoothness on a slab of plate glass,using fine Carborundum or other suit-able abrasive compound.

The cylinder group of componentsshould now be assembled on the mainframeplate, complete with joint pack-ings as required, but the outer endcylinder cover should be left for thepresent to enable the piston to bemoved easily, or removed entirely ifrequired, in the course of fitting. Thecrosshead can now be screwed on to

Continued on page 655

651

e

More about sparks from steamU NDER the heading “Sparks from Steam,” the letter and theillustration in Postbag for October 1 last, from Mr H. H.Nicholls greatly interested me, having had experience of thesephenomena without any special apparatus, which I describedin MODEL ENGINEER for January 15 under “ Blue Sparks on aSummer’s Night “; also because I had the original machineright under my nose in the Municipal Museum of Science andEngineering, Newcastle-upon-Tyne.

This, the prototype of the subject of Mr Nicholls’ illustration,had only one cone to direct the steam on to the brass comb.In the illustration three cones are shown, thus indicating amuch larger machine, and I have since learned that a verypowerful apparatus was installed and used at the PolytechnicalInstitute in London, having no less than forty-six steam jets.It was capable of producing sparks almost two feet long.

I am sorry to have to disagree with Mr Nicholls about thesteam being superheated. The pipe mentioned is apparentlyprovided to carry off the steam arising from the water in thechamber, which actually is a condenser; the gauge glass thatindicates the water level in this chamber can be plainly seen.The pipe could also act as a stay bracket for the chamberto steady it against the reaction of the steam jets. At anyrate it could not be of much importance as it was not providedon the prototype, and must have been added as a refinement.The steam, of course, was admitted to the condensing chambervia the stopcock on the top of the dome.

In the prototype the collecting comb is mounted differentlyfrom that in the illustration. Instead of being mounted on theboiler the comb is carried on an insulated column, after themanner of an electric floor standard lamp, a coil of insulatedwire being attached for conducting the experiments.

The well-made horizontal double-acting steam engine, nowplaced under the boiler to conserve space, was used to maintainthe water levels in the boiler and the condensing chamber,the pump being driven by an eccentric on the crankshaft. Thewhole is built in a massive manner and is no doubtthe original machine constructed by W. G. Armstrong 125years ago. The three-cock water gauge on the boiler, iffitted with a guard, would seem in keeping with today’spractice. No pressure gauge or thermometer is fitted; thepressure possibly being kept up to blowing-off point whenusing the apparatus. Several unused rivet holes were left,possibly to aid combustion, while the fire-lid appears to haveendured some drastic increase in air admission below the gratearea.

Jeynes’ CornerI

A commentary on current topics

The following is extracted from an Elementary Treatise onNatural Philosophy of 1875 AD by Deschanel:

“About the year 1840, W. G. Armstrong (later Lord Arm-strong) invented an electric machine, in which electricity wasgenerated by the friction of steam against the sides of orificesthrough which it was allowed to escape under high pressure.

“It consists of a boiler with a fire inside, supaorted onfour glass legs; the steam, before escaping, passes through anumber of tubes, which traverse a cooling box containingwater, into which dip meshes of cotton, which are led over thetubes and passed around them.

“The cooling thus produced in the tubes causes partialcondensation of the steam; this has found to be an indis-pensable condition, the function of perfectly dry steam beingquite inoperative. Strictly speaking it is the friction of thedrops of water against the sides of the orifices, which gener-ates the electricity, the steam merely furnishes the means ofapplying the friction. The jet of steam becomes positivelyelectrified, while the boiler becomes negatively charged.

“ The positive electricity is collected on a metal combcommunicating with an insulated conductor. The steam ischecked in its course by a metal tongue, round which it hasto pass before it can enter the wooden tube through which itescapes into the air.

“The machine to work well requires a pressure of severalatmospheres; the water in the boiler should be distilled. If asaline solution be introduced into the tube through whichthe steam escapes, all traces of electricity disappear.

“The generated electricity varies both in sign and degreeaccording to the liquid whose particles are carried out bythe steam, thus when a small quantity of oil of turpentine isintroduced into the jet of steam, the boiler becomes positivelyand the steam negatively charged.

“At the Polytechnical Institute in London, there was amachine with a boiler 78 in. long, and a diameter of 42 in.,and having 46 jets. This machine was extremely powerful, andsparks were obtained at a distance of 22 in.”

STERN-WHEELER

Continued from page 651

the piston rod, and by checking itsdistance from the frameplate at bothends of the stroke its alignment andthe exact position of the slide-bracketcan be established.

Reference has been made to thevalve rod guide, which is fitted to theframeplate on the opposite side to theslide-bracket. To line up the guide, thevalve rod is placed in position, through

MODEL ENGINEER I September 1965

the gland and into the tail guide, andthe distance between the projectingpart of the rod and the frameplate isthen measured with inside calipers ona slide-gauge. The guide casting, witha piece of 1/8 in. rod fitted through thebore, is laid on a flat surface and thedistance from this to the rod similarlymeasured. The surface of the seatingmay be machined or filed down till themeasurements coincide exactly. Errorsin fitting can- be made good by fittingshims between the frame and the guide,but it is better to avoid the need forthem. The vertical position of the

fixing holes in the guide can be locatedby spotting from the frameplate, orvice versa. These observations applygenerally also to the fitting of the slide-bracket.

The instructions for machining andfitting have so far been applied to theset of parts for one side only of theengines, but it will readily be under-stood that they are applicable equallyto the other side, so long as theirreversal from right to left hand isobserved where necessary.

To be continued.

655

ENGINES FOR A STERN-WHEELERContinued from September I by Edgar T. Westbury

WORKTHE slide-bars are made from rect-angular mild steel bar 3/8 in. wide X 5/16in. thick. After checking the straight-ness and flatness of each piece, the endsshould be machined or filed to 1/8 in.thick for the specified lengths and therest tapered down each way from thecentre.

The object of making them thisshape is to obtain maximum rigiditywithout excessive thickness; if they areparallel throughout, at the major sec-tion they would look unnecessarilymassive and heavy.

A hole is drilled and tapped at thecentre in each of the upper bars totake a lubricating cup. One end ofeach bar is attached by a single studto the flat seating on the cylindercover boss, and the other end to theinside seating of the slide bracket. Asalready mentioned, the componentsshould be located and lined up so thatthe crosshead and piston rod assemblywill slide freely over the full lengthof stroke without binding on the top,bottom or sides of the slide-bars.

The connecting rods are unusuallylong in comparison to those of mostother steam engines, and to avoid ex-cessive weight it is recommended thatthey should be made in the form oflight alloy castings. Apart from trim-ming to remove flashes and rough spots,the only essential machining is the bor-ing and fitting operations on the bigand little ends. The design of big end(or crankhead bearing) specified, incorp-orates a gap piece secured by a gib and

cotter. Some constructors may con-sider this difficult to machine and fitproperly. As an alternative, it is per-missible to use a solid big end, but itwill then be necessary to modify thecrankpin to allow the bearing to beassembled.

To fit the gap piece, the inside facesof the forkend should be machinedtrue and parallel. This may be doneby clamping the rod, flat side down,in the lathe toolpost and using a sawor slotting cutter running on an arborbetween centres or in the chuck. Ifno other tool is available, a single-point fly cutter set crosswise in a boringbar will do the job. The gap piece ismade to a close fit in the fork, and across-hole is drilled through the assem-bly and filed out to 1/8 in. square. Whenalmost to finished size, a broach ordrift made from 1/8 in. silver steel maybe used to produce a true, smooth bore.

In the detail drawing of the cotterand gib, it will be seen that the twoparts are complementary to each other,and are both tapered on their matingsurfaces o n l y to a very small angle.Both parts are made from 1/8 in. sheetor strip mild steel, and there is no ad-vantage in making them out of anyharder material. The cotter is just aplain wedge, but the gib has projectionsat both ends which should fit closelyacross the outside of the big end forkand prevent it from spreading. Whenthe parts are fitted and the cotterdriven in fairly tightly, the gap pieceshould be held in place securely and

TAP UPPER BARS ONLY FOR LUBRICATORS

SLIDE BAR 4 M.S.-

726

properly located. In the event that itmay subsequently be necessary to takeup wear in the bearing, the inner sideof the cross-hole in the fork, and theouter side of that in the gap piece,may be eased with a file.

The bore of the bearing housing maybe filed out to slightly under finishedsize, prior to boring and reaming. Forthese operations, the rod may beclamped to the side of an angle platemounted on the lathe cross-slide, atright angles to the lathe axis. A man-drel held in the chuck may be used tofind the centre location of the bore.

The most suitable tool for boringthe bearing housing is an offset boringhead, but if this is not available a smallboring tool may be held in the four-jaw chuck and adjusted to the radiusrequired. A reamer or D-bit may beused for finishing to size, and the twoside faces of the bearing housing maybe machined with a cutter set in a3/8 in. boring bar. After the two crank-head bearings have been dealt with,the rods may be held in the reverseposition on the side of the angle plate,for drilling, reaming and facing thelittle ends.

The simplest way to machine thesplit crankhead bearing is to take apiece of cast bronze or gunmetal stick,with ample outside machining allow-ance and long enough to provide achucking piece. After drilling under-size, the piece is split right throughlengthwise, the faces trued up, andtemporarily sweated together. Thepiece is then re-chucked for boring andturning externally to finished size, thenparted off. Mark the parts for identi-fication before separating them by heat-ing. When fitted to the crankheadhousing, the halves may be located, andprevented from rotating by a spigot onthe end of the lubricator.

Rectangular steel bar, 7/16 in. X 1/4 in.,may be used for the web of the crank-head, with the crankpin made separ-ately, pressed in and flush riveted atthe back. Alternatively, the componentmay be made in one piece, machinedfrom solid with integral crankpin.

MODEL ENGINEER I October 1965

hs” C’sUNK _ N GAP PIECE FITTED SEPA R A T EL Y

CONNECTING ROD

E D I NE T E D

;

CRANKHEAD 2 O F F M.S.

I OFF EACH R.H. & L.H. L . A .

The built-up construction will gener-ally be found easier and satisfactory ifproperly carried out, though brazingmay be preferred to a press fit. In anycase it is important that the crankpinaxis should be in true parallel align-ment with the bore which fits the mainshaft.

A simple way to ensure this is totake a piece of bar long enough to makeboth crankheads, and after markingout the hole positions, to clamp itacross the lathe faceplate with each ofthe hole centres in turn set up fordrilling and boring. An alternativemethod, which also ensures that thetwo cranks have exactly the samethrow, is to cut separate lengths andsweat them together on the flat faces,then mount them edge-on to an angleplate by a strap or two clamps. Theangle plate is shifted on the lathe face-plate to centre each hole in turn fordrilling and boring the two piecestogether.

By mounting the web on a 5/16 in.mandrel, the back face can be machinedto 7/32 in. thickness at the outer end.

LOCKING SCREW

RETAINING’SCREW TAPER2’

COTTER cre-

2 OFF EACH MS.-

CUDCEON PIN 2 O F F M.S.- -

The crankpin should be machined tofinished size, with about 1/2 thou inter-ference fit in the web, and about 1/32 in.extra length; the hole to receive itshould have the burr removed at thefront, and a slight countersink at theback for flush riveting. In the eventof using a solid crankhead bearing, thepin cannot have a retaining collarformed on its outer end; this must bemade as a separate piece, preferablylike a large-headed screw but withouta screwdriver slot, as this is entirely outof keeping with correct practice andlooks unsightly. The crankpin, in thiscase, must be centrally drilled andtapped, and a grubscrew can be in-serted from the inner side to lock thecollar screw. Do not split the web ordrill the cross-hole till the web is fittedto the main shaft.

The gudgeon pin can be turned frommild steel bar, to 9/32 in. maximumdiameter on the head, 3/16 in. on theshank, and reduced to 1/8 in. dia, forscrewing 5 BA on the end. It issecured in the crosshead by a nut onthe inside, and it may be prevented

M O D I F I E D C R A N K H E A DF O R S O L I D B E A R I N G

C R A N K H E A D B E A R I N G

2 OFF BRONZE

from rotating by a snug key at theback of the head, though this shouldnot really be necessary.

The link reversing gear designed forthis engine follows the principles of theStephenson gear, but it is modified indetail in order to simplify it and re-duce the number of parts, also to con-form with the low centre line of thevalve gear and the restricted move-ment of the link which it entails. Itmay be observed that marine enginescannot utilise the advantages of “ link-ing up” to the same extent as loco-motives, and therefore exact control oflink position is of less importance.

This is because the load conditionsof the two types of engines are entirelydifferent. Locomotives encounter theirmaximum resistance to movementwhen starting a heavy load from rest,and run more lightly at high speed,except on gradients. Marine engines,on the other hand, start quite easilyfrom rest, but the load increases steeplywith the speed. Under normal con-ditions of service, expansive workingof the steam is possible only to a

MODEL ENGINEER I October 1965 727

5 MACHINED

DIE BLOCK.TTACHED TO BAR

METHOD OF MACHINlNG

LINKS & DIE BLOCKS

_

/-3,& T5P 6 B.A.

/ TAPER 10”

REVERSING LINK

2 OFF M.S.

limited extent in marine engines ofthe “simple” type; that is, in a singlestage as distinct from compound ortriple-expansion engines.

Most marine engines run at or nearfull gear, and are controlled mainly bythe throttle, or as it is generally termed,the “ manoeuvring valve.” Unlike loco-motives, model boats do not have anengine driver on the spot to adjust thecontrols to best advantage, and thoughremote control of the link gear of theengine is possible, it has never beenattempted, so far as I know.

The special feature of this valvegear is the use of an open-ended link,having minimum overall length inrelation to its effective arc of move-ment, and capable of being machinedaccurately without special equipment.It allows either eccentric rod to bebrought into exact horizontal align-ment with the valve rod, so that theonly link slip at full gear is that causedby the link suspension gear. As the artic-ulated joints are not on the centre lineof the link, the working thrusts areslightly offset, but this is not a seriousmatter in view of the length of theeccentric rods in relation to theirtravel. The ahead eccentric rod isarranged to line up as directly as pos-sible with the link, but the astern rodis cranked to make up for the necessaryendwise displacement of the eccentricsheave. As engines are normally runin the ahead direction, and only re-versed for brief periods, this arrange-ment works quite satisfactorily.

To be continued.

GEARLESS CLOCK MOVEMENTContinued from page 723

must be done carefully, as if you filetoo far the cutter will be too narrow,and if you do not file enough therewill be a negative clearance at the sidesof the cutter. Harden and temper to astraw colour in the usual manner.

When I first read about this way ofmaking gear cutters, I was not veryimpressed. They looked so weak andthe method of getting the side clear-ance appeared to me rather doubtful.However, I have made many like thisnow and have never had one break.In fact, recently I had to cut two largegears in dural, both of 20 d.p. Onehad 96 teeth and the other 84. Thelarge one was 3/16 in. thick and the other1/8 in. I made a silver steel cutter in just

728

the way I have described and cut allthe teeth in both gears with it, takingthe full depth out in one cut or pass,and without breakage. I would notadvise them for cutting mild steel, butfor brass and dural they seem excellent.

Fig. 22 shows the general arrange-ment for cutting the minute wheel (36teeth). The blank is turned to sizeon the little mandrel, which is grippedin a collet chuck. The home-madecutter is held in an adaptor and grip-ped in the chuck of the ME millingspindle, which is driven by a plasticbelt and an electric motor mounted onthe rear end of the lathe bed. A simplestop can be set t o prevent you fromrunning the cutter against the chuckand breaking the tip off.

Indexing for this particular wheelrequired the use of a compound gear

train. All the other gears can be in-dexed by using a single wheel. Fig.23 shows the change wheel quadrantwith the detent engaged in the bottomwheel. In order to take up the back-lash, a weight is hung on the end of apiece of string which is wrapped roundthe chuck. Figs. 22 and 24 show theidea.

Fig. 25 shows the smaller pinionafter being cut and about to bereamed 3/32 in. with a home-made reamerin the tailstock chuck. After reaming,it is cut off and the other pinion cuton the next turned portion. Both pin-ions have a portion turned down. Theminute pinion to be riveted in theminute wheel and the cannon pinion tofit the clamp collar. This one must beslit with a hacksaw as well.

To be continued.

MODEL ENGINEER I October 1965

ENGINES FOR A STERN-WHEELERContinued from October I by Edgar T. Westbury

THE REVERSING GEARA S the machining of the links anddie blocks is an important operation,which some constructors may con-sider difficult, I propose to deal withthis before describing other parts of thevalve-gear.

The links are made of mild steel, andthe pair may be machined at one oper-ation from a piece of flat bar 1-1/4 in.wide X 5/16 in. (or more) in thickness,and slightly less than 7 in. long. Holesare drilled approximately 5 in. apartto allow the bar to be bolted across themiddle of the lathe faceplate, where itis mounted and set up symmetricallyboth axially and lengthwise of the bar.Before bolting it in position, a slip ofthin, soft sheet metal, such as copperor aluminium, should be interposedbehind it, so that there is no danger ofdamaging the faceplate when the toolruns through it in turning the outsideor parting off.

First, the outside edges of the barshould be turned to a diameter of 6-7/8in., or in other words, 3-7/16 in. radius,as specified on the detail drawing. Asthe operations on these componentsall involve intermittent cutting, theydemand a cautious approach with thelathe running at low speed, keen andproperly set tools and well-adjustedslides. A parting tool may be used toproduce a “witness” cut marking theinside radius of the link at 6-1/8 in. dia.(3-1/16 in. radius), but for obvious reasonsit should only penetrate to a shallowdepth at this stage. Note that a partingtool, when presented axially to thework to cut an annular groove, musthave increased side clearance on theouter side.

Undercutting toolThe parting tool can also be used

to rough out the channel of the linkto a depth and width slightly under3/16 in. to allow of finishing and pro-ducing the included taper of 10 deg.on the sides. A special tool will be re-quired for this-in fact, it will gener-ally be found best to use separate tools,each fed in turn at an angle of 5 deg.

MODEL ENGINEER 15 October 1965

on the topslide, for the two sides. Withdue care, a clean and accurate finish canbe produced on the essential surfaces.It is difficult, or perahps impossible, tocorrect errors or clean up the surfacesby after-treatment. When the channelhas been machined, the parting toolmay again be used to penetrate the barand separate the pair of links from it.

The principles employed in mach-ining the die blocks are generally simi-lar, but in this case short pieces ofbronze or gunmetal may be used,roughly cut to shape, but well over-size and temporarily fixed to a flatbar of steel or other metal which is

on a superfine file or lapping plate.The links are drilled and tapped

on the back face for the pivot pins,which must be securely and perman-ently fixed in position, and must notproject on the inside of the channel.As their length is limited, they shouldbe prevented from becoming loose bytinning the threads and sweating themin position. The flanged centre stud isused for the suspension of the link, andmust project well beyond the othertwo pivots so as to clear the knuckleends of the eccentric rods.

The eccentric straps may be madefrom bronze or gunmetal castings, or

TAP 8 B.A. 8 B.A;CLEAR

ECCENTRIC ROD & STRAP MS.& BRONZE ‘/e DIA.

again mounted symmetrically acrossthe lathe faceplate.

The segments may be sweated inposition, but both location and securitywill be improved if in addition they aredrilled and counterbored for the pivotscrew, and the bar drilled and tappedto take it. Still better, the pieces mayeach be made long enough to producetwo die blocks, and secured by two

screws in each. This will producetwice as many die blocks as required,but spares are always useful. The seg-ments can then be machined on bothinner and outer sides to the same anglesas the links, which can be “offeredup” for checking up on the fit. Theyshould preferably be fitted on thetight side, as the die blocks can beeased by rubbing down the front face

they may be machined from stockmaterial. In either case, allowanceshould be made for the metal removedin splitting, and also for facing the two

sides.A good way of ensuring uniformity

in the shape and size of the four strapsis to use a piece of material thickenough to make them all, plus chuck-ing and parting-off allowances, and ofcorrect external shape. This may beset up in the four-jaw chuck, boredundersize, and the straps parted off.Before splitting them, the holes shouldbe drilled and tapped, and temporaryscrews fitted to hold the halves togetherduring subsequent operations. Do notforget to mark the pairs to identifythem for correct assembly. The strapsare then chucked and bored individu-

745

TAP

UCKLE 2 OFF- - M. 5.

LOOSE ECCENTRIC

ARRANGEMENT OF SLIP ECCENTRIC VALVE GEAR

B.A.

KNUCKLE PIVOT2 &

LUBRICATOR- -4 OFF BRASS- -

LINK IN MID GEAR STARBOARD CRANKPfN

ECCENTRIC SHEAVE4 OFF M.S.

ally, and one side faced true with thebore; to face the reverse side, they maybe clamped on a shouldered mandrel.

Sheet or strip steel, 1/16 in. thick, isused to make the rods, which are 5/16+ in.at the large end. They are attached tothe straps by 3/32 in. rivets. The seatingson the lugs of the straps are steppedback to half their thickness, and theyshould be flat and true, with the endsof the rod butted against the shoulder.To promote rigidity of the joint, thesurfaces of both parts may be tinnedand sweated together after riveting;better still, they may be silver soldered.The same applies to the offset knuckleat the other end of the rod, which isonly held on by a single rivet.

Note that if the straps are providedwith lugs to take a lubricating cup asshown, they should be assembled toproduce right and left-hand pairs.The distance between the strap centreand the knuckle pivot should be thesame for all four rods, and as thereverse rods are cranked to line theknuckles up with the links, allowanceshould be made for the slight shorten-

746

ARRANGEMENT OF REVERSING VALVE GEAR (PORT ENGINE)

ing which this involves. Care shouldbe taken to see that the inner face ofthe knuckle is flat and parallel to theface of the strap, also that the pivothole is square with it and a good fit onthe link pivot. The thickness of theknuckle should be such that no endplay is allowed when the retaining nutand washer are fitted to the pivot, butthe rod should articulate quite freely.

The eccentric sheaves are machinedfrom solid mild steel bar, and the sim-plest way to make them and to ensureaccuracy and uniformity is to startwith a piece of material long enoughto make all four, with chucking andparting-off allowances. This is firstfaced truly on the end and marked off,with the throw centre at 1/8 in. from themain axis, to give a full travel of 1/4 in.The bar is then set up in an eccentricfixture, such as a Keats V-angle plate,and centre-drilled, drilled and reamedfor the required depth for the foursheaves. It is then re-set to run trueon the external surface, for turningeach sheave to fit the strap, and partedoff, leaving a rim 1/32 in. thick.

PORT CRANKPIN

When assembled, the sheaves are dis-posed face to face, so that their rimsare on the outer sides of the straps.No harm will be done if the straps rubagainst each other, but rubbing can beprevented by interposing a thin washerbetween each pair of sheaves. A sunkgrubscrew, preferably of the socket-head type, is fitted to a hole drilled andtapped through the thickest part of thesheave, to secure it to the shaft whenits position has been adjusted.

The valve rod knuckle is made from1/4 in. square mild steed, which is firstset up in the four-jaw chuck to run astruly as possible, for facing, drillingand tapping to fit the rod. It is thenparted off at 3/4 in. long, cut away tohalf its thickness for a length of 3/8 in.,and drilled and tapped crosswise forthe pivot on which the die block artic-ulates. The head of this pin must notproject beyond the face of the die block,and when screwed into the knuckleand adjusted to take up end play, it islocked by a nut on the outer end.

In order to obtain the proper opera-tion of the slide valve, and to eliminate

MODEL ENGINEER 15 October 1965

lost motion as much as possible, it isimportant, with this form of valve gear,where slightly offset thrusts are inevit-able, to avoid end play in pivotedjoints. It has already been observedthat the range of link movement is res-tricted by the low centre line of themotion work in relation to the deck ofthe boat. Even so, it will be necessaryto provide a shallow well or recess toprovide clearance for the lower end ofthe link and the astern eccentric rodin full ahead gear.

Though it is not possible to fit andadjust the valve gear until all parts ofthe complete pair of engines are madeand assembled, the diagram showingthe arrangement and disposition of itsparts will help to explain how it oper-ates. The means of suspending andshifting the link are not shown, butthis will be subject to some variationto suit the design of the hull and themethod of control adopted. By mov-ing the link up or down, either of thetwo eccentric rods can be brought intoline with the valve rod, thereby vary-ing its timing to suit the direction ofrotation required.

Quartered cranksIn intermediate positions, both timing

and travel of the valve are modified toinfluence the lead and cut-off, so that inthe mid-position, the eccentric motionscombine to provide shortened valvetravel and mean timing. The angularpositions of the eccentrics, in relationto the crankpin are roughly indicatedon the diagram, but the exact settingdepends on various factors, includingthe amount of motion lost in the link,die block and pivots. Note that thecranks of the port and starboard en-gines are displaced at right angles toeach other, or in locomotive parlance,“ quartered.” It does not matter, fromthe practical point of view, whichcrank is in the lead; there may possiblybe some conventional rule about this,but I have not found any reference toit in marine engineering textbooks. Asthere are no coupling rods to take intoaccount, slight inaccuracy in quarter-ing the cranks does not affect working;the eccentric settings are related to theindividual cranks, as for totally separ-ate engines.

There are, no doubt, some construc-tors who do not wish to provide fullycontrolled reversing valve gear forthese engines, and will be quite satisfiedeither with a non-reversing gear or asimplified reversing arrangement. It isquite in order to fit a single, fixedeccentric sheave to the shaft, with its

rod connected directly to the valve rodknuckle. Alternatively, slip eccentricreversing gear may be fitted, in whichthe eccentric sheave is not fixed to theshaft but is driven by a dog whichallows a certain angular motion ineither direction before taking up thedrive. This arrangement is shown inthe drawing, where it will be seen thatthe dog has part of its circumferencecut away to clear the pin fixed in theside of the sheave. The amount of freemovement allowed for the designedvalve setting is approximately 120 deg.,but it may be varied to suit lap andlead-and not by shifting the dog(which should always be set in sym-metrical relation to the crank) but byaltering the angle of cutaway.

End location of the sheave is pro-vided by the fixed dog on one side andthe main bearing on the other; itshould be fitted to turn freely on theshaft, but it should not be too slack.With this simple arrangement, the boatwill run either ahead or astern if givena slight push off in the required direc-tion, but no provision can be made forexpansive working, or for remote con-trol of reversing.

Oil cupsThe small lubricating cup shown in

the drawings is suitable for fitting tothe slide bars and the crankhead bear-ings; for the latter, it may have a pilotspigot on the end of the thread tolocate the joint of the split bearings butit should not bear hard against them.Open-topped cups similar to thisappear to have been fitted to many ofthe early stern-wheelers; or perhapsthey may have originally have had lids,which subsequently got lost. Theymay have been provided with internaltubes for wick syphon feed, but it ismore likely that they were intended tocontain tallow or other animal fat. Oilof really good lubricating quality, inthose days, was scarce and relativelyexpensive.

The oil cups illustrated can beturned from 1/4 in, brass rod in onepiece, and the simplest method is toface one end, drill 1/16 in. and counter-bore, then part off and reverse in thechuck for shouldering down and screw-ing the small end. A 3/16 in. end mill,or a drill ground square across the end,may be used for counterboring the cup,though the angle formed by an ordin-ary drill point is permissible so long asit does not unduly weaken the base ofthe cup. Round off the angle of theoutside with a hand tool, if no suitableform tool is available. Flats may be

cut on the reduced diameter, to enablea thin spanner to be used for screwingthe cup into position.

It may be possible to obtain ready-made lubricators of a size small enoughto suit this purpose, but it is importantthat they should be inconspicuous, andnot of a type obviously intended forsome other kind of machine, such as abicycle, as these small details are theones which are always pounced uponby voracious critics.

The crankshaft, which is made from3/8 in. dia. steel bar, forms a part of thepaddle wheel assembly, and its lengthwill depend upon the beam of the hull.When this is determined, and the twosets of mainframes are connected bythe cross member, the extreme ends ofthe shaft should each project 1/4 in. out-side the main bearings, to accommo-date the crankheads. The shaft shouldbe set up truly for centre drilling andturning down the ends to 5/16 in. dia.for a length of 1-1/8 in.

Make the shaft a tight wringing fitfor the crankheads, which are then setin position at 90 deg. to each other.The cross holes are drilled and reamedto take closely fitted bolts. The bossesof the crankheads are then sawnthrough to form split clamps.

(To he continued)

MODEL ENGINEERINGSUPPLIES

A new name in our advertisementpages, but not a new one to people in engineering, is Henry Righton and Co.Ltd.

For several years this company hasspecialised in meeting the requirementsof technical schools, colleges, handi-craft centres and public institutions.

Large stocks of non-ferrous metalsare held at the company’s six brancheswhere the trade counter is open toindividual callers. The addresses of thebranches and a representative selectionof items they stock, which may be ofuse to the model engineer, are listedin the full-page Righton advertisementon the back page of the October I

issue.

ERRATUMIn the drawings of the feed pump for

Maid of Kent bv Mr K. N. Harris.page 678 September 15 issue, the bordwas inadvertently given as 9/16 in. Thisshould, of course, have been 1/2 in., asgiven in the detail drawings of thepump body and the ram.

MODEL ENGINEER 15 October 1965 747

ENGINES FOR A STERN-WHEELER

Continued from October 15 by Edgar T. Westbury

Paddle wheel constructionT HE paddle wheels of early stern-wheelers were usually fabricated inwrought iron, with rigid floats. Articu-lated or feathering paddles such aswere used on many large seagoingsteamers, were not used on any stern-wheelers so far as I can ascertain.

Their advantage did not amount tomuch when the immersion of thepaddles was shallow and fairly constantbut the main objection to their usewas mechanical complication and lia-bility to damage. Logs and other half-submerged debris often played havocwith paddle wheels, and a simple,easily repaired structure was obviouslyto be desired. For the same reason,the floats were commonly made oftimber which could readily be obtainedwhen replacement became necessary.

In a working model, strength andrigidity of the paddle wheel are~essential, but heavy or cumbersomeconstruction should be avoided. Thereis some latitude in the kind of material,and my original idea was to useduralumin or similar light alloy for

the hubs and frame components. Butit has not been found possible toobtain rolled or extruded angle sectionin this metal small enough for makingthe radial members or spokes. Brass isthe next best material, and it willprovide the necessary strength, thoughwith a substantial increase in weight.It has the advantage that the completestructure can be sweated together toimprove rigidity and eliminate riskof trouble due to imperfect riveting.

The two hubs may be turned andbored at one setting. They shouldbe a tight fit on the shaft, and whenfinally located they should each besecured by a properly fitted taper pin.A taper reamer or broach should beused to ream the holes through huband shaft in situ, and if standard taperpins are not obtainable, the pinsshould be machined to the same taperas the reamer, so that they fit the holesthroughout their full length. It ispermissible to use parallel pins as analternative, but they must be equallywell fitted, as any slackness will not

’ CRANKSHAFT e

2 OFF BRASS OR L.A. SPOKE 12 OFF EACH R.H.& LH. BRASS OR L.A.

only affect the strength of the structure,but also lead to hammering witheventual shearing or distortion of thepins. The cross holes should prefer-ably be drilled at right angles to eachother, as shown.

It is important that the rivet holesin the hubs should be equally spaced,at uniform radius, and the use of anindexing device for the lathe mandrel,together with a drilling spindle, isrecommended at least for locatingthe holes. This operation can be carriedout before parting-off each hub, oralternatively, the finished hub can bemounted on a stub mandrel for drilling.The inner face of the hub should bemachined flat and square with the axis.

To make the frame bracing rings,pieces of 1/16 in. sheet material about3-1/4 in. square may be mounted on awooden backing plate by screws in thefour corners, and set up on the face-plate or in the inverted jaws of thefour-jaw chuck. A trepanning tool maythen be used to cut the inside circle,or a small parting tool with ample

RIVET HOLES IN ALL PARTS 1/16" DIA.

EQUALLY SPACED

u-

__--

- 1. .-yl6-/

FLOAT 12 OFF L.A. OR LAM I NATED BAKELITE BRACING RING 2 OFF BRASS OR L.A.

MODEL ENGINEER I November 1965

MODEL ENGINEER I November 1965

side clearance, presented endwise onto the work, will serve the same pur-pose. Before cutting the outer circleand thus detaching the ring from itsmount, the rivet holes in the ring maybe located and drilled in the same wayas those in the hub. It is possible tomachine both rings at once by mount-ing the two plates together and thusensure that their essential dimensionsare identical.

The spokes must all be of identicallength, and with rivet holes correctlylocated, in order to produce a sym-metrical and true running frame. Notethat one flat face of each spoke is seton the radial line, and that the spokeson opposite side frames are right- andleft-handed so that the other flat facewill fit against the inner face of therespective hub. The inner ends of thespokes are tapered off at 30 deg., andif properly fitted they will lock eachother in place, with their extremeends in contact with the shaft.

Using a jigI strongly recommend the use of a

simple jig to shape the ends of thespokes to the correct angle. It can bemade from solid rectangular bar, withthe groove milled in it, or it can bebuilt up by riveting three pieces oflighter material together. The dimen-sions shown cn the drawing are onlytentative; the essential thing is thatthe strips must be held in correctlocation sideways and endwise, andthe jig held at the correct angle in thetoolpost or on the cross-slide; this maybe set with the aid of a protractor oreven a set-square.

A side or end mill, or even a thicksaw, mounted in the chuck may beused for milling the edge of the strip.One set of I2 spokes is clamped edgeupwards, but the other set must havethe flat side upwards, and will thereforerequire a square or rectangular packingstrip slightly thicker than the innerdimension of the angle strip, and withthe corner rounded or chamfered.When once the cut has been adjusted,the saddle should be locked so that allpieces are treated exactly alike.

The jig may be readjusted to chamferthe outer end of the spokes at 45 deg.(make certain that the right comer iscut away) and it may also be used fordrilling the rivet holes by providingguide holes in the top and rear side.

Before carrying out this operation,a check should be made to ensurethat the holes will line up with thosein the hub and the bracing ring. Itmay be found that, to make the spokes

805

JIG SET UP IN TOOL POST

MILL OR SAW PACKING PIECE

JIG FOR MILLING & DRILLING ANGLE STRIPS

D I E B L O C K _2 OFF

BRONZE

fit closely together and also againstthe shaft, their ends may have to betrimmed; if so, all should have thesame treatment, and hole locationstaken from tnis end.

Owing to the restricted width ofthe spokes, there is very little roomfor the rivet heads, and if standardsnap-head rivets are used it may benecessary to file flats on the heads sothat they will clear the inside of theangle. A ball-pein hammer should beused for the initial closing down ofthe rivets, followed by the use of aconcave rivet punch just deep enoughto shape the end neatly without mark-ing the surface of the material. Asimilar concave depression in thesupport or “ dolly ” will help to locatethe head of the rivet.

Some care is necessary in all smallriveting operations to avoid distortionor marring of the rivets. Rivets shouldfit the holes closely; and it will generallybe found that the length allowed forclosing them should be somewhat lessthan the “ one diameter ” prescribedin the textbooks. Too long an allow-ance increases risk of distortion andmay cause the rivet to harden beforeit is neatly closed down. A large head

806

does not necessarily mean a firmer hold.If the frame is to be sweated to-

gether, the contact surfaces should betinned before riveting, and whenassembled the frame should be uni-formly heated to fuse the joint. Alittle extra solder may be added, butnot more than is absolutely necessary.Remember that thin sections of metalare liable to distortion when locallyheated and so do not play a torchflame indiscriminately over the work.It is better to heat the assembly on athick plate over a gas ring or bunsenburner.

Both side frames should be assembledand lined up on the shaft so that thefloats, when attached, are truly parallelwith the shaft axis. It is not advisableto sweat them permanently to theframes; in the interests of light weight,the floats may be made of hard lightalloy or laminated resin plastic boardsuch as Tufnol or Paxolin.

If all parts have been made to uni-form dimensions, the assembled paddlewheels should be in correct balance,but it is a good policy to check up onthis by rolling the shaft on parallelstrips, such as steel rules clamped onedge at a suitable distance apart andlevelled both individually and witheach other. Any correction requiredmay be made by filing the ends of thespokes, or by judicious trimming ofthe floats. It is not necessary to go tothe extent of true dynamic balancing,in view of the low speed of the paddlewheel.

When the paddle shaft is fitted tothe main bearings, and other workingparts are connected up, the valve gearcan be set to give correct timing atfull ahead and astern positions. Theeccentrics of both port and starboard

engines should first be set approxi-mately to their positions in relation tothe respective crankpins, but theirgrubscrews should only be set up tightenough to prevent inadvertent move-ment at this stage.

The ahead eccentric on either sideis first used to check valve travel, byturning the shaft to produce the fullmovement of the valve rod in eitherdirection. This applies whether thedouble-eccentric link motion, slip, orfixed eccentric is used. The steam-chest cover is removed to allow in-spection of the slide valve, and thetail-end guide is also removed so thatthe valve rod can be adjusted with asmall screwdriver. In this way theslide valve can be set to give equalcylinder port openings at each end ofthe travel, and the valve rod is thenlocked to the knuckle by the lock nut.

The exact timing of the aheadeccentric is then adjusted by setting thecrank at inner and outer dead centresin turn. Some readjustment of theeccentric may then be required toproduce an equal amount of openingof the cylinder ports, in other words,“ lead,” at each crank dead centre,without altering the adjustment ofthe valve rod. Only a very small leadis required in engines of this kind, andfor a given eccentric travel and cylinderport location it can only be changedby altering the lap, or the distanceby which the slide valve overlapsbeyond the cylinder ports at each endwhen in mid-travel. Such alterationnecessarily entails changing the overalllength of the slide valve, and it isonly called for when making majorexperiments in valve setting.

The astern eccentrics are set in a(Continued on page 811)

MODEL ENGINEER I November 1965

~ READERS'QUERIESGeneva Mechanism

I would be grateful if you could giveme sources of reference on the GenevaMechanism, a3 I am experiencing diffi-culty in obtaining information for asixth form applied science project, whichis to be submitted for examinationpurposes--SK., Wirral.

The device known as the GenevaStop Motion was originally used to pre-vent overwinding of clocks and watchesby limiting the number of turns whichcould be applied to the spring arbor. Ithas been adapted to many other pur-poses where intermittent motion is re-quired, such as counters, indexing gears,and for the film shift in cinematographmechanism. This is perhaps the best-k n o w n m o d e r n a p p l i c a t i o n , a n d f o rpractical reasons it is usually designedto give four 90 deg. shifts per revolutionof the driven shaft; in this form, it isc o m m o n l y k n o w n a s t h e “ M a l t e s eCross ” mechanism.

The arrangement shown in the draw-ing gives smooth acceleration in eitherdirection of shift, and positive locking

PIN ENTESLOT

MALTESE CROSS MECHANISM

while stat ionary. I t is important thatthe pin should enter the slot exactlyon its radial line, and that the cutawayof the driving disc should unlock thecross at the same instant. Similar princi-ples apply for mechanisms giving anynumber of shifts, but the proportionsshown are correct only for a I-shif tmechanism.

I would very much like to constructmy own magnetiser in order to enlivensome of my model locomotives withweak magnets (all 12 v. d.c.).

Could you kindly explain the princi-ple used in this work and details of thesize of a transformer required? Also,

The intensity of f ield necessary formagnetising will depend on the natureof the steel in the magnet treated, andthe cross section of its poles. For thesmall magnets of model locomotives, anexcitation equivalent to 1,000 ampere-turns should be sufficient. This can beobtained at the most convenient voltage;that is, by using a suitable combinationof turns in the field windings, and appliedcurrent (i.e. 1,000 turns at I ampere, or100 turns at 10 amperes for instance). Itis generally best to use a low-voltagesource of supply, such as car batteries,for excitation, as a transformer andrectifier for high voltage would be largeand expensive. Only a momentary ap-plication of current is necessary, and thecircuit must be broken as sharply aspossible by a heavy duty switch.

similar way, and before replacing thesteam chest covers, a check should bemade at both ahead and astern positionsfor each cylinder. No discrepancies intiming should arise unless there areerrors in eccentric throws or length ofeccentric rods. Permanent fixing ofthe eccentrics to their shafts may beassured by tightening the grubscrews,and more positive keying should notbe necessary. There is always a riskthat in drilling a dimple in the shaftto locate the point of the screw, somedeviation from the true setting mayoccur.

MagnetisingWhere possible, the magnet should be

magnetised in its circuit assembly ratherthan separately. The north pole of themagnet should be presented to the northpole of the magnetiser, and it is there-fore essential that the polarity of thefield windings should always be the

The steam connections to the portand starboard cylinders may be ar-ranged to suit convenience in installa-tion, but the steam flow to eachindividual cylinder should be free andunrestricted. A single stop valve,capable of fine adjustment, should befitted to the common supply pipe orthe branch junction.

To be concluded

MODEL ENGINEER I November 1965 811

* Queries must be within the scope of this journal and only one subjectshould be included in each letter.

* Valuation of models or advice on selling cannot be undertaken.

* Readers must send a stamped addressed envelope with each query andenclose a current query coupon from the last page of the issue.

* Replies published are extracts from fuller answers sent through the post.

* Mark envelopes “ Query,” Model Engineer, Braywick House, Maidenhead.

are the north and south pole con-nections critical ?

It is understood a large d.c. flashcurrent is required.-G.M.H.B., Fareham.

A magnetiser consists essentially ofan electro-magnet capable of producinga h igh- in t ens i t y f i e ld wh ich can be

same. For magnets having mult iplepoles, it is necessary to use a magnetiserwith equivalent numbers of poles, or tomake adaptor pole pieces to serve thesame purpose.

Some experiment in the vol tage ofsupply may be necessary for the bestresults.

N (N( )S) S

14 SWG. ENAMEL COVERED WIRE

E L E C T R O - M A G N E T F O R M A G N E T I S I N G M O T O R M A G N E T S

a p p l i e d t o t h e p o l e s o f t h e m a g n e tunder treatment. Several methods areemployed to produce the magnetic field,but the simplest for your particular pur-pose, assuming that the magnets to bedealt with are all of the simple two-poletype, would be to use a d.c. electro-magnet having a solid or built-up softiron carcase, with a winding on one ormore limbs, and pole pieces (adjustableto fit the magnets if necessary).

Engines for a Stern-wheeler . . .

Continued from page 806

ENGINES FOR A STERN-WHEELERConcluded from November I by Edgar T. Westbury

Reversing control gearALTHOUGH the controls are not generally regarded as a partof the engines, they serve an essential purpose in the workingof the complete installation, and anyone building a workingmodel stern-wheeler will need to equip it with control gearof a practical and representative type. The means ofshifting the reversing links were indicated in the generalarrangement drawings, but the details of construction ofthe components must necessarily depend on the hull designand convenient positions for operating the controls. For

QUADRANT FRAME

LINK SPRING LATCH

nected to the central pivots of the reversing link. For end-wise location of the weighshaft, the standards are fitted closeup against the inner sides of the lifting arms, and theseare then pinned to the shaft in exact angular alignment witheach other.

As an alternative, the standards may be made withoutangle brackets, and attached to the inner sides of the mainframes. They are more rigidly supported, but being morewidely spaced the weighshaft is more liable to deflection,

TAP 10BA

ATE NOTCHES BY TRIAL 7

this reason, the drawings given here are subject to modifi-cation to suit individual requirements.

The weighshaft, to which is attached the lifting and re-versing arms, is simply a length of 1/8 in. steel rod carriedin bushes at either end, supported in standards which aremounted on the cross-member between the engines. Theycan be made from 1/16 in. sheet steel, in the form of A-frames,with angle brackets riveted to the base and bushes pressedor sweated in at the top. A tie bolt is fitted between thestandards to stiffen the structure.

Fretting out of the apertures is optional, and their dimen-sions are not specified, but they lighten the structure andimprove appearance. The location athwartships of’ thestandards is determined by that of the lifting arms, fromwhich the lifting links should hang vertically when eon-

kI ! i !llll !P

,I ‘IQUADRANT PLATE

1/

?&IA.

LEVER

unless made larger in diameter, and it will also need to beprovided with end location collars. Stern-wheelers usuallyhave a more or less vertical spray screen immediately for-ward of the paddle wheel, and this is sometimes used asa mounting for the weighshaft bearings and other partsof the control gear, but this is only possible if the supportsof the screen are rigidly strutted to the deck.

The lifting and reversing arms are best made by machin-ing from solid 1/4 in. square mild steel, though they can bebuilt up by silver soldering if it is more convenient. If theformer method is used, the hole in the boss should firstbe drilled with a No 31 drill and reamed to a wringing fiton the weighshaft. A 1/8 in. stub mandrel should then bemade with the end screwed to take a nut to clamp the leverin position. The outside of the boss can be turned circular

MODEL ENGINEER I5 November 1965 823

Method of lapping cylinders

CONNECTION

QUADRANT REVERSING GEAR ASSEMBLY

on each side, and the side faces machined as far aspermitted.

It is also possible to cut the slot in the fork of the liftingarm with a narrow parting tool, while in this position, if astop pin is fitted to the mandrel to prevent the workslipping on the pin. If desired, the reversing arm may beincreased in length, or provided with more than one holefor attaching the reach rod, to suit the range of the controlgear. This arm is pinned to the shaft at right angles to thelifting arms, in an endwise position to line up with thecontrol lever, which may be amidships but are more oftentowards the port or starboard side of the deck.

It will be seen that the lifting link is fitted with a longbush at the lower end where it fits the pivot of the reversinglink. Its object is to ensure that the link swings in a truearc instead of tending to wobble sideways because of offset

824

thrust. The bush may be made of bronze and sweated in(this term is intended to include either soft or silver solder-ing, the latter being much superior in strength of the jointin all cases); the shank of the link is made of 1/16 in. sheetor strip steel. Similar material may be used for the reach rodif it is not too long, but the adjustable rod of 1/8 in. roundbar with screwed and lock-nutted knuckles will enable thegear to be more accurately adjusted. The pivots for thevarious joints may be in the form of 3/32 in. or 7 BA bolts,with plain shanks which fit closely in the holes.

The engines of even the smallest stern-wheelers weretoo large to be conveniently reversed by a direct-acting handquadrant lever; the usual arrangement appears to be ascrew gear with multi-start thread and a large diameterhandwheel. But this is one item in which I consider thatfidelity must be sacrificed to utility in a working model asthe manipulation of a screw would be slow and awkward inthe limited space. The quadrant gear, though suited mainlyto locomotives and stationary engines of comparatively smallsize, is much easier to operate by hand. As shown here, itdoes not exactly follow any prototype but is designed to bebuilt as simply as possible, while looking something like theorthodox type.

The quadrant frame is made from 1/16 in. sheet steel, witha riveted angle bracket at the base for mounting on the deckof the boat, in the most convenient operating position, andat such a height that the reach rod is approximately horiz-ontal. To obtain the proper range of movement from fullahead to full astern, the lever and reversing arm should bevertical, and the lifting arm horizontal, when in the midgear or “neutral” position of the reversing link. The leveris also made of 1/16 in. steel, with the top end narrowed downinto a tenon, which can be screwed or sweated into ahandle turned from 3/16 in. steel rod. It works on a pivotbolt, guided between the frame and quadrant plate, over arange of about twenty degrees either side of the centralposition. Spacer bushes 3/16 in. dia., of a length which justallows free movement of the lever, are fitted to the quadrantbolts, and the pivot bolt has an 1/8 in. journal of the samewidth, with the rest of the shank screwed 6 BA to fit atapped hole in the frame, where it is secured by a lock-nutat the back.

To make the trigger, a piece of 1/32 in. or 20 g. sheet steel,a little over 3/4 in wide by 7/8 in. long, should be folded overa bending strip slightly over 1/16 in. thick, with roundededges. This will produce the shape shown in the plan view,and when this is neatly formed the unwanted metal can becut away to the required contour. To form the concave curveof the outside, the trigger should again be placed on thebending strip, and hammered along the inner edge of thehand grip. The latch is made from 1/16 in. steel, with thedetent filed to the shape shown, and drilled and tapped10 BA at the ends to take the pivot screw and the stoppin.

A groove is turned in the head of the pivot screw to locatethe bend of the latch spring, which is made of 20 gaugepiano wire bent to the shape shown. It is held in position atthe back of the lever by a IO BA screw so that it bears onthe stop pin of the latch. A link bent from 18 g. s tee lwire, or cut from solid sheet steel connects the latch to thetrigger. The pivots may be in the form of IO BA or 1/16 in.bolts, with the heads as small and unobtrusive as possible,but where permanent assembly is permissible, 1/16 in. rivetsare generally neater. Only two notches on each side of theneutral position are shown on the quadrant plate, givingfull and three-quarter linkage ahead and astern, but more

MODEL ENGINEER 15 November 1965

I '/;2 DIA. Y4' DIA. "2 DIA. ' I I

3

LIFTING ARM 2 OFF REVERSING ARM

2 OFF LIFTING LINK

i--l ?!I6

t--

STANDARD 2 OFF LENGTH AS REQUIRED t --- ADJUSTABLE REACH ROD

can be added to extend the range if desired. I t is best to locate these notches by trial, after the assembly has been fixed to the deck and the reach rod has been adjusted for mid-gear.

While the quadrant gear is recommended for hand oper- ation, remote control of any kind may be carried out more effectively by screw gear, powered by a servo-motor. I have not attempted to show this mechanism, as it may be varied to suit individual choice, but I suggest that a screw 1/4in. dia., Whitworth (20 t.p.i.) could well be used, driven through worm gearing from a miniature reversible electric motor. Contacts or limit switches may be fitted to stop the motor at each end of the travel. Itt is also possible to control the reversing gear by a non-reversible motor with a worm- geared crank, connected directly to the arm on the weigh- shaft; but in this case all controls must be carried out in rotational sequence, which is not always convenient from the aspect of the transmitter.

One or two other details of the engine installation may be briefly dealt with. I t has already been mentioned that the cylinders should be lagged, mainly with a view to appear- ance rather than thermal efficiency. Though conservation of heat is more desirable than ever in small engines, it is very difficult to insulate the cylinders effectively because, however well they are wrapped up, much heat is lost by con- duction to the frame and other adjacent metal parts.

Generally, the only attempt at insulation of small cylinders

I OFF ALL PARTS IN MILD STEEL

is by lagging the barrel, while the greater areas of end covers and steam chest are left exposed. The actual insul- ating material may be felt, flannel or asbestos matting, packed in the recessed space around the cylinder. This, is covered and held in place by an outer casing or " cleading," attached in any convenient way to the cylinder.

The simplest from of cleading is sheet metal, wrapped around to fit neatly between the cylinder covers, and held top and bottom by small screws along the edges of the flat cylinder surfaces. Blued sheet steel is usually recommended for this purpose, but it is best suited to engines of relatively modern types. Earlier engines employed wooden battens held in place by brass straps; whether these are truly characteristic or not, they are certainly pleasing in appear- ance and not at all difficult to fit.

Hardwoods such as oak, teak or mahogany are preferred; the strips may be cut in the lathe with the aid of a small circular saw and an improvised table with adjustable fence, to a width of 3/16in. X 1/32in thick. To simplify fitting, they may be glued to a backing of tough paper or tracing linen. Alternatively, a single sheet of veneer, scored by means of a stylus or blunt scribing knife with lines 3/16% in. apart, may be used. The cleading bands should be thin and unobtrusive, and the largest screws which can be used to hold them in position are 100 BA, with undersize heads.

In case the overhang of the cylinders forward of the main Continued on page 839

MODEL ENGINEER 155 November 1965 825

some materials being supplied free by the many willingand skilful members.

The Round Pond was built by the members in 1957, andis to international standards. It is 100 ft in diameter, withconcrete sides and an asphalt bottom. It is stocked withfish which keep the water free of algae.

Level is kept constant by ball cock from the town mains.In a hot climate like this, with an evaporation of 5 ft peryear and an annual rainfall of only 21 in., a water bill ofabout £25 a year does not seem excessive. The pond is thescene of much activity by the model boat enthusiasts andcompetition in speed events is keen in the 5 C.C. and I0 C.C.hydroplane class.

A variety of excellent working scale models of liners, tugsand other craft make an eye-catching display on the placidwaters of the pond.

The working model stationary steam engines are suppliedwith steam from a vertical fire-tube boiler, 24 in. X 9 in.,burning coal and evaporating about 30 lb. of steam perhour. Steam engines range in size from about 3/4 in. bore upto a couple nearing 3 in. bore X 6 in. stroke, several of themconstructed in the last century. The beam engine, built in1846, is reputed to have been the first actual steam engineimported into this colony. Referred to by the locomotivemen as the Steam House, it is also the club workshop, witha workbench, a large power drill and grinder.

Steam is the ruling interest behind all members’ activities-locomotives, boats and stationary engines-but two diesel

While no major additions are at present planned, thereis no doubt that with its steadily increasing membershipand wider interests of members, the society will continueto grow on the firm base already established, and thus pre-serve, if only in miniature, the age of steam. q

View of the multi-gauge track curving towards the clubhouse

Steaming-up bay, a traverser serving twelve roads

STERNWHEELER.. . Continued from page 825

engines have recently appeared and the speed events on thepond are, of course, in the i.c. field.

There is a midget racing car track; cars are also i.c. andattain fantastic speeds.

The SA Society, formed in 1927, has grown from amodest beginning to an active and virile group of enthusi-asts. The decision in 1947 to acquire ground and establishpermanent facilities has been fully vindicated and the pre-sent members look back with gratitude to the planners andworkers who have made the Park possible.

frames should be considered to cause instability, it is pos-sible to fit an additional cross-member on the deck, attachedto the underside of the cylinder steam chests. The exhauststeam from the cylinders should, properly speaking, betaken to a condenser, but as this is hardly practicable in amodel, the next best thing is to lead it into a separatorvessel which collects oil and free condensate, then releasethe remaining steam to atmosphere through the funnel orsmokestack. Unless highly superheated steam is used, enginelubrication can be kept to the minimum, and a simple dis-placement lubrication in the common steam line is capableof fulfilling requirements, but a more positive mechanicallubricator, as used on locomotives, may be fitted if desired.

I have not designed a boiler specially for these engines,but there are several types which can easily be adapted forthe purpose, including locomotive boilers, which conformto the type generally used on small stern-wheel vessels ofearly date. Sometimes the boilers were housed more or lessamidships, but in a few cases they were mounted, fully ex-posed, on the foredeck. Boiler firing of model marine boilersis most conveniently carried out by means of a liquid fuelor butane burner, as solid fuel is not easy to apply in thisparticular instance, unless a special type of boiler withhopper-fed furnace, is employed.

Questions may be asked about the method of steeringused on stern-wheelers. Because of the shallow draught,the effective depth of the rudder was limited, and oftentwo or even three rudders were used. They were fitted in thespace immediately forward of the paddle wheel, coupledtogether and operated through chains and pulleys from anorthodox steering wheel. El

MODEL ENGINEER 15 November 1965 039