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Machine Anatomy
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C o u r s e I n v o l v e d : G r a d u a t e D i p l o m a i n Te c h n o l o g y E d u c a t i o nU n i v e r s i t y o f L i m e r i c kD e p a r t m e n t o f D e s i g n & M a n u f a c t u r i n g Te c h n o l o g yL e c t u r e r / Te a c h e r : M r. J o s e p h Ly s t e r A c a d e m i c Ye a r 2 0 1 2 : S p r i n g S e m e s t e rTe c h n i c a l S u p p o r t : M r. J o e M u r r a y & M r. R i c h i e H e n n e s s yN o t e s P r e p a r e d b y: M r. J o s e p h Ly s t e rAv a i l a b l e o n w w w. s l i d e s h a r e . n e t / W T 4 6 0 3
WT5912TECHNOLOGY EDUCATION & WORKSHOP PRACTICE 2: MATERIALS AND CONSTRUCTIONUNIT 2 – WEEK 3
UNIVERSITY of LIMERICKOLLSCOIL LUIMNIGH
Machine Anatomy and Construction Studies Detail
MACHINE ANATOMY
WT5912
ThicknesserSurface Planer
Rip/Panel Saw
-Machine Parts-Machine Design-Machine Function-Machine Safety/Use-Machine Processes-Machine Maintenance
When planing wooden material a number of factors combine to generate the flat surface.
Number of cutting knives in the blockSpeed of the revolving blockFeed speed of the materialKnife cutter designChip breaking aidsNature and species of the material
SURFACE PLANER
MACHINE PARTS
MACHINE DESIGN: CIRCULAR CUTTER BLOCK
• Reduced noise levels
• Better balance
• Safer clamping mechanism
• Can run head at higher speeds (RPM)
• Can produce better finish
• Easier and quicker maintenance
Department of Manufacturing & Operations Engineering
Department of Manufacturing & Operations Engineering
KNIFE CLAMPING MECHANISM
MACHINE DESIGN: CIRCULAR CUTTER BLOCK
CUTTER PROJECTION
Use of a limiter to achieve limited cutter projection
Department of Manufacturing & Operations Engineering
MACHINE DESIGN: CIRCULAR CUTTER BLOCK
CUTTER PROJECTION
The cutter projection and the shape of the block face cause the severed chip to bend back causing a crack across its width
This makes long grain riving less likely(Chip breaker not shown)
MACHINE DESIGN: CIRCULAR CUTTER BLOCK
MACHINE DESIGN: PLANER KNIVES
Planer Knives Important factors when selecting a planer knife Suitabil ity for cutter block
Material being processed
Finish required
Volume being machined
Clamping and setting mechanisms
Planers can have 2,3,4,6……. Cutter knives.
Most smaller machines such as those found in schools will have 2,3 or 4 knives.
MACHINE DESIGN: PLANER KNIVES
Knives can be made from Chrome Vanadium steel alloy.
This is suitable for machining softwoods and non abrasive hardwoods.
However with advances in machining technology better materials have been developed to machine wood and wood composites.
Chrome Vanadium knives dull quickly on harder more dense material.
This requires more sharpening, setting up and leads to a lot of time wastage.
MACHINE DESIGN: PLANER KNIVES
High Speed Steel (HSS) is a cobalt steel alloy with a small percentage of Tungsten added.
It is more suitable for machining all types of wood than the chrome steel compounds.
Abrasive stock should be machined using solid or tipped cutters.
Tungsten Carbide (TC) is the best tool compound for machining manufactured boards.
For general work HSS cutters are preferred to TC Cutters can be re-sharpened easily. A keener edge can be achieved on HSS giving a better
fi nish
The reason for this is that steel compounds are smelted and shaped by rolling and forging while the metal is close to melting point.
The molecules of the compound flow and align themselves in response to this pressure giving the material maximum strength and edge holding capabilities
Department of Manufacturing & Operations Engineering
MACHINE DESIGN: PLANER KNIVES
Tungsten carbide is a sintered compound. The fine grain powder from which the cutter will eventually will be made is compressed into a mould ( the ‘blank’ un-edged cutter required) under extremely high temperature (1500C) and pressure to form a solid block.
Tungsten does not flow – it retains a granular structure and will chip rather than deform if abused.
Department of Manufacturing & Operations Engineering
MACHINE DESIGN: PLANER KNIVES
Because if its brittle nature TC cutters require a more obtuse sharpness angle than the HSS cutters (more support for the cutting edge).
This makes it less satisfactory for cutting softwoods than HSS knives which can be ground to a more acute cutting angle.
Department of Manufacturing & Operations Engineering
MACHINE DESIGN: PLANER KNIVES
CutterKnife
TC
KnifeCutter
HSS
Large grinding angle
to support cutting edge
Smaller grinding angle
produces keen edge
Department of Manufacturing & Operations Engineering
MACHINE DESIGN: PLANER KNIVES
MACHINE FUNCTION: KNIFE CUTTER GEOMETRY
Rake or Cutting angle
Angle created between the face of the cutting knife and the centre of the cutter block
Can have a wide range
Softwoods 27° to 35 °Hardwoods 15° to 25
°
CuttingAngle
Department of Manufacturing & Operations Engineering
Bevel or Lip Angle
Angle formed to give the cutting edge
Minimum of usually 35°
Greater for tipped cutters
BevelAngle
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION: KNIFE CUTTER GEOMETRY
Clearance Angle
Angle formed between a line tangential to cutting circle and the bevel angle of the knife
Must be presentHas a bearing on the
life of the cutting edge
Usually 10° to 15°
ClearanceAngle
Cutter CircleDiameter
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION: KNIFE CUTTER GEOMETRY
Peripheral Cutting Speed
A constant speed in the range of 35-45 m/s will give best results
Increase in speed may cause loss of dynamic balance due to vibrations
Poor finishIncreased noise
levels
Cutter Circ leDiameter
CutterRotation
Work Movement Direction
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION: KNIFE CUTTER GEOMETRY
Combination of a rotary cut and a linear feed will leave the surface of the material with a series of arcs on it called Curtate Trochoids
The pitch and depth of these arcs will determine how smooth the surface finish will be
PITCH DISTANCE
Work PieceSlower Feed Rate
Work Piece
Pitch
Pitch
tt
t = Cutter arc depth on machined surface
Fast Feed Rate
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION
PITCH DISTANCE
2mm to 3mm for non obvious joinery and painted external work.
1mm to 1.5 mm for internal painted work.
0.5mm to 1mm for hardwood joinery and furniture.
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION
PITCH DISTANCE
The SI unit of time is the second , but the minute is acceptable.
Feed rate on wood working machines is expressed in metres
per minute. (m/min) The formula for the pitch of the cutter marks is given by:
fp = -------
nR where p = p i tch of cutter mark
f = feed rate
n = number of eff ect ive cutters
R = revo lut ions per minute of b lockDepartment of Manufacturing & Operations
Engineering
MACHINE FUNCTION
PITCH DISTANCE
The unit for “p” will be metres (m) f m/min m minp = ---- = --------- = ----- x ------ = m
nR 1/min min 1
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION
PITCH DISTANCE
Problem 1
Calculate the cutter pitch of a 4 cutter block revolving at 4200 rev/min with a feed speed of 24m/min.
F 24 24p = ------- = ------------ = --------- = 0.0014m = 1.4mm
nR 4 x 4200 16800(Internal painted work)
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION
PITCH DISTANCE
If a graded surface is specified and the machine has a multi-speed feed gearbox, the same formula is used but “f” is expressed in terms of n ,p, and R.
f p = ------- f = nRp
nR
Department of Manufacturing & Operations Engineering
MACHINE FUNCTION
MACHINE PROCESSES: CHIP FORMATION
Department of Manufacturing & Operations Engineering
MACHINE SAFETY AND USE
MACHINE SAFETY AND USE
MACHINE SAFETY AND USE
MACHINE SAFETY AND USE
MACHINE SAFETY AND USE
MACHINE SAFETY AND USE
MACHINE SAFETY AND USE
Continuous improvement
MACHINE SAFETY AND USE
RISK MAGNITUDE
MACHINE SAFETY AND USE
RISK ASSESSMENT
Chip breaking aid and pressure bar prevent riving and splintering
Department of Manufacturing & Operations Engineering
MACHINE PROCESSES: CHIP FORMATION
MACHINE MAINTENANCE
Cutter and Machine Maintenance Involves: 1. Grinding and setting of knives 2. Roller and pressure bar setting 3. Prevention of resin build up on table and rollers. 4. Attention to:
bearing wear feed complex adjustments rise and fall table
Department of Manufacturing & Operations Engineering
GrindingThe grinding angle of a cutter can vary between 30
to 35This is increased to 40 for hardwoods (cutting edge
lasts longer)
OverheatingMay produce micro cracks in the cutting edge which
can run into gaps when the cutter is used.May cause the cutter to bow due to expansion.
Department of Manufacturing & Operations Engineering
MACHINE MAINTENANCE
Overheating can be avoided By taking light cuts.
By ensuring that the grind wheel is ‘dressed’ when required to ensure that the face is open and not glazed when grinding the knives.
By using a ‘soft’ grinding wheel on HSS cutters – the soft structure of the wheel allows its grains to break away as soon as they are blunt revealing sharper ones.
By wet grinding – this is the grinding of cutters while partially submerged in a mixture of water and soluble oil. The water is a coolant to prevent frictional heat developing and to disperse it should it occur. The oil prevents rust in the cutters and it provides a degree of cutting lubrication.
Department of Manufacturing & Operations Engineering
MACHINE MAINTENANCE
Setting Cutters in Block
Before setting the following points should be checked. The out feed table and cutter block must be clean and free
from dust resin. Method of adjusting cutters.
Area where setting device is used from should be free from resin and damage.
Straightness of cutters.
Cutters correctly balanced both in weight and end for end.
Department of Manufacturing & Operations Engineering
MACHINE MAINTENANCE
Setting of knives will greatly depend on the type of cutter block
Knife cutter projectionChip breakerKnife parallel to tableAll knives in the same peripheral cutting
circle(Refer to machine manual for setting)
Department of Manufacturing & Operations Engineering
MACHINE MAINTENANCE
Setting devicesThere are a number of cutter setting devices.This device and procedure will often be supplied with the
machine.They can be loosely placed into the following four categories: 1. Bridge device 2. Precision cutter setter device 3. Pin locater device 4. Wooden straight edge device
5. Cutters require accurate setting in the block because if the knives are not revolving in the same cutting circle a poor fi nish will be produced.
Department of Manufacturing & Operations Engineering
MACHINE MAINTENANCE
MACHINE PARTS: THICKNESSER
MACHINE PARTS/USE: THICKNESSER
MACHINE SAFETY AND USE
Continuous improvement
MACHINE SAFETY AND USE
RISK MAGNITUDE
MACHINE SAFETY AND USE
RISK ASSESSMENT
CIRCULAR SAWING MACHINES
NOTE Circular sawing machines are high risk woodworking machinery
Pupils should not be permitted to use this machine.BS 4163:2000
The machine should be included in a planned maintenance program that should include electrical safety tests.Read Circular Sawing Machines (Week 6 Notes)
MACHINE PARTS: RIP/PANEL SAW
MACHINE DESIGN: SAW BLADE
Hook AngleEdge
ClearancePitchGulletPlate TensionRiving KnifeTable SlotGuardsFence
MACHINE DESIGN: SAW BLADE
TOOTH CONFIGURATION
The shape of the saw blade tooth and the way the teeth are grouped also affect the way the blade cuts. The configuration of the teeth on a saw blade has a lot to do with whether the blade will work best for ripping, crosscutting, or laminates.
Of course, no matter which tooth design you're looking at, more teeth will give you a smoother cut than fewer teeth.
MACHINE DESIGN: SAW BLADE
TOOTH CONFIGURATION
MACHINE DESIGN: SAW BLADE
TOOTH CONFIGURATION
A ripping blade will have a Flat Top Grind (FTG) for fast cutting with the grain.
A cross cut blade will do the best job with an Alternating Top Bevel (ATB), cutting across the grain like a knife and producing a very smooth cut. A blade with Triple Chip Grind (TCG)
is good for all-purpose cutting and also gives you a very clean cut. TCG blades are also good for cutting non-ferrous metals and plastics.
MACHINE DESIGN: SAW BLADE
TOOTH CONFIGURATION
In general, blades with more teeth yield a smoother cut, and blades with fewer teeth move material faster.
A 250mm blade designed for ripping wood can have as few as 24 teeth, and is designed to quickly move material along the length of the grain.
A rip blade isn't designed to yield a mirror-smooth cut, but a good rip blade will move through wood with little eff ort and leave a clean cut with a minimum of scoring.
MACHINE DESIGN: SAW BLADE
TOOTH CONFIGURATION
A crosscut blade is designed to give a smooth cut across the grain of the wood, without any splintering or tearing of the material.
A crosscut blade will usually have from 60 to 80 teeth. More teeth mean that each tooth has to cut less material.
The result is a cleaner cut on edges and a smoother cut surface. With a top-quality crosscut blade, the cut surface will appear polished.
MACHINE DESIGN: SAW BLADE
HOOK ANGLE
In both Rip and Cross-cutting saws the Hook angle determines
The feel of the cut The quality of the finish The power consumed
The approach angle of the saw varies according to the relative position of the tooth in the downward cutting arc.
This angle alters from the top plane of the timber where the tooth top makes fi rst contact to compress the timber before the tooth point engages, to a plane where the tooth angle and the timber face are parallel.
MACHINE DESIGN: SAW BLADE
HOOK ANGLE
Hook Angle
MACHINE DESIGN: SAW BLADE
HOOK ANGLE
The amount of Hook determines the degree to which the tooth will drive into the timber during the cut.
The effect is of the timber being drawn forward.
The greater the hook angle the greater this tendency.Too great of a hook angle will result in Harsh cut Tearing Poor finish Less rigid tooth Vibration.
MACHINE DESIGN: SAW BLADE
HOOK ANGLE
A blade with high positive hook angle (+20°) will have a very aggressive cut and a fast feed rate.
A low or negative hook angle will slow the feed rate and will also inhibit the blade's tendency to "climb" the material being cut.
A blade for ripping wood on a table saw will generally have a high hook angle, where an aggressive, fast cut is usually what you want.
Radial arms saws and sliding compound mitre saws, on the other hand, require a blade with a very low or negative hook angle, to inhibit overly fast feed rate, binding, and the blade's tendency to try to "climb" the material
MACHINE DESIGN: SAW BLADE
HOOK ANGLE
On most saw blades, the tooth faces are tipped either toward or away from the direction of rotation of the blade, rather than being perfectly in line with the centre of the blade.
Hook angle is the angle formed between the tooth face and a line drawn from the centre of the blade across the tip of the tooth.
On a blade with a positive hook angle, the teeth are tipped toward the direction of the blade's rotation.
A negative hook angle means that teeth tip away from the direction of rotation, and a zero degree hook angle means that the teeth are in line with the centre of the blade.
MACHINE DESIGN: SAW BLADE
MACHINE DESIGN: SAW BLADE
MACHINE DESIGN: SAW BLADE
GULLET
The gullet is the space cut away from the blade plate in front of each tooth to allow for chip removal.
In a ripping operation, the feed rate is faster than in crosscutting and the chip size is bigger, so the gullet needs to be deep enough to make room for the large amount of material it has to handle.
In a crosscutting blade the chips are smaller and fewer per tooth, so the gullet is much smaller. The gullets on some crosscutting blades are purposely sized small to inhibit a too-fast feed rate, which can be a problem, especially on radial arm and sliding mitre saws.
MACHINE DESIGN: SAW BLADE
MACHINE DESIGN: SAW BLADE
GULLET
The gullets of a combination blade are designed to handle both ripping and crosscutting. The large gullets between the groups of teeth help clear out the larger amounts of material generated in ripping. The smaller gullets between the grouped teeth inhibit a too-fast feed rate in crosscutting
MACHINE DESIGN: SAW BLADE
MACHINE DESIGN: SAW BLADE
CLEARANCE
Work clearance must be provided.
The saw tooth provides this clearance.The ‘Kerf’ produced by the teeth must be wider than
the supporting saw plate.Steel saws had the kerf formed by bending or
‘setting’ alternate teeth laterally.With tipped saws the tips are wider than the saw
plate and thus create the clearance.Clearance or relief bevels are ground on the sides
and the top of each tooth.
MACHINE DESIGN: SAW BLADE
PLATE TENSION
A flat disc will remain flat and true if turned at a slow speed.
When variable stresses are created on this disc due to: Braking eff ect of sawing Heating eff ect of friction Outward pull of centrifugal force
the outer rim area of the disc will expand.
If the whole area of the disc can expand at the same rate the disc will remain flat and true.
This does not happen with a saw blade.The central region of the blade is clamped between the
collars and does not expand.
MACHINE DESIGN: SAW BLADE
PLATE TENSION
Only the teeth of the saw blade should make contact with the work and a portion of the energy expended in cutting will unavoidably be converted to heat.
The periphery of the blade will therefore tend to warm up more quickly than the main plate body.
This will cause the periphery of the blade to expand. If this is not taken into account the blade will distort. To prevent this saw blades are ‘tensioned’ during the
manufacturing stage. Rim speed will determine the amount of tension required
in a particular saw blade. Thinner saw blades require greater tension. Faster saws require more tension.
MACHINE DESIGN: SAW BLADE
PLATE TENSION
Traditionally this was done by highly skilled labour but modern saw manufacturers use machine operated rollers to achieve a faster more uniform result.
This within limits allows the plate to expand uniformly in uneven temperature gradients.
A blade which has lost its tension will be seen to be throwing from side to side.
This is most noticeable as the blade slows down after the machine is switched off.
If this is the case the blade should be removed and sent for servicing.
This can be reduced by cooling the blade tip while in operation by packing.
MACHINE DESIGN: SAW BLADE
PLATE TENSION
TC tipped blades have an extremely long life and to assist the tension factor, slots are incorporated around the edge of the blade.
These allow a degree of individual expansion between segments on the plate edge.
They also break up harmonic frequencies, which build up during the sawing process.
MACHINE DESIGN: TABLE SLOT
MACHINE DESIGN: TABLE SLOT
MACHINE DESIGN: TABLE SLOT
MACHINE DESIGN: RIVING KNIFE
MACHINE DESIGN: RIVING KNIFE
MACHINE DESIGN: RIVING KNIFE
MACHINE DESIGN: RIVING KNIFE
MACHINE DESIGN: RIVING KNIFE
MACHINE DESIGN: RIVING KNIFE
MACHINE DESIGN: BLADE GUARD
TOP BLADE GUARD
Covers the top edge of the saw blade.
Deflects waste.
Prevents accidental contact with the uppermost teeth of the blade.
It can also limit the eff ects of material rejection.
MACHINE DESIGN: BLADE GUARD
MACHINE DESIGN: BLADE GUARD
MACHINE DESIGN: BLADE GUARD
MACHINE DESIGN: RIP FENCE
Rip Fence Setting
MACHINE DESIGN: RIP FENCE
RIP-CUT CROSS-CUT
SETTING
MACHINE FUNCTION: CALCULATIONS
MACHINE FUNCTION: CALCULATIONS
MACHINE SAFETY AND USE
Continuous improvement
MACHINE SAFETY AND USE
RISK MAGNITUDE
MACHINE SAFETY AND USE
RISK ASSESSMENT