F/86 AERO 330 331 PAGE 3-5

SHEET METAL BEND LAYOUT

Ir'>JFORMATJ or~ SHEET

An airplane structure consists predominately of oarefully designed sheetmetal parts. Most of these parts have been given form by bending. Very preoise methods have been developed for the lIlR.king of sheetmetal layouts where bends are involved. Whenevesr formad sheetmetal parts must be made to olose tolerances or when they must fit, or match other parts, an aoourate flat layout is neoessary. In almost any type of fabrication aocuraoy in layout saves time, material, rework and trimming. Layout is the initial step, all processBs whioh follow are built upon the layout foundation.

o 0

DRAWING

LAYOUT

PART

FIGURE-I

The ~neral ;:>rocedure for laying out the nat ahape of a part can be divided into three simple problems:

-- pi- ;. 1. Detemining stock size or where to cut.

2. iDeating brake reference lines or where to bend.

J. Marting centere to indioate wh!'ll"e to drill or punch.

F/86 AERO 330 33:1 PAI3E :3-6

B0fore beginning the study of bend layout 70u lmst have a clear understanding of the terms involved.

'l'ermE Used in Bend layout

BEND RADIUS (R) 'oIben sheet metal ,ie bent, the angle formed vill not be sharp but vill folloll the arc of a circle. The radillS

of this arc i9 called the "bend radiUl!l·. The bend radius is 1I>9a=ed ~m a radiue center to the inside S'tlrt'sce of the metal.

Bending both stretches and shrinkll the mtal. The I!lBtal on the inside of the bend ahrinkB or is squ6l'l:MId together, lIhile on the outBide of the bend it i8 stretched. Figure:2 SholiS the change that takes place in a bend. Most sheet metal u5ed in aircraft is l!lBi!e of etrong and corre !3]lOndingly brittle alloys lIhich 1!Il8.y crack or become 1'10 li9aXaned as to fall in service if bent too sharply. The kind of metal, ita thickness and ita tamper determine the mini= eat'e bending radius. The recol!!l!lended minimum bend radii for several aluminum alloys and magnesium are given in the Standard UAL bend radius chart in Figure 13. These bend radii are normally given on the print.

--, , ,

--

\ , , ,

r---BEND RADIUS

THIS PART SHRINKS

THIS PART STRETCHES

BEND RADIUS

FIGURE 2

Bending has the effect of strein hardonlnf; the metal vith a resulting increase in brittleness. \lith cladded =terial it is poaail:>le for cracks to have oc­cuI:r'6d'in the alloy, but not be visible through the sort coating. Bending brakel!J or form blocka l!Jhould ahlBYS be checJcad to eee that they viII' provide the proper radiul!J.

liE1J1'R!L LINE \Ii thin the mlr'Ved portion of metal loIhich has been bent, there 111 an imaginary 11ne called the "oeutral line". On this J ioo

the eompresl!Jion on the inside of the bend changes to tension on the outside of the bend. The oeutral line repreeentB that part of the mtal, in the bend,

F/86 AERO 330 331 PAGE 3-7

whieh is the saJ>e length af'teIr bending lUI it WItS before bending. When _tal ill bent, the bent area ill 10 to 15 percent thinner than before bending. 'l'hil! 1m beoause the JIlet..U !!!Ovel! IlION eaeily in Ualll3ion than in ooBpre!!sion. Af'ter the zetal !IIOYeS beyond its elastic liJcit the I!ltrength of the IC0tal on the inside of the bend (compresaivo I!ltr-ength) beCOJ:lS1I greatar thllIl the I!ltrength of the metAl on the outside of the bend (tension IIItrength). Due to thiB thlnnl ng the neutral line of the _tal moves in tovard the radiUl! center. P'igare .3 sboVl! the position of the nll>utrd liOll vithin a bend.

NEUTRAL LINE 3~ TO 45":; OF 'P FROM INNER SIDE OF BEND

---. __ --,-.l -------- T

T· THE NEUTRAL LINE

FIGURf: .3

.. ' .

mIll LIl'IE DIMENSIONS 'l'bere are &ovoral ways of dimensioning formed lIheet-IlOetal parts on drawings. The lOst common 1a the

outside Dr "llIlOld l.ine" diloension (MID). A mld line dimenaion is the distance troll! the edge of the metal to e. point in space called the RJIIOld point". The llIlOld point is the point of inter!l$Otion of lines extended from the outside lI1Irfaees on either sid!! of the OOM, ! ~ld ~ 11: m.n ~~'7 11M in flPaee. parl!i.l:""l to t.'>", ooz:d, ez>5. Pi.l.fS,,:1.l:;g-through ~ ][DId pc:.l.:i!t!>. l4!l1::lld line would be the outside oornsr of the part if there vilre DO r-euiius.

JruID TANGEN'!" LDlE DIME:NSI01IS Lines can be drawn aeroBs nat _tal which will iDdioate t.ne bouniarlers of a bend to

be JZaJ:ie. Suob lines must be located where the surface of the unbent uection -1'!l t.angent to the are of the radiUII. ThelNl lines where the bent and unbent

metal Beet IlN called "Bend Tangent Lines" (BTL). Dimensions whicb give the length of the unbent llleotion are known lUI "Bend 'rangtmt Line Diloenaionll" (BTIll) •

DlSIDE DD!ENSIOKS On IIOl'iII!I ps.rt.m tho most oritical dimanllion ma;r be to 1m

inside ImrfD.eS, for GXlD!p1e. betwsn the flanges of m. channel that 10 to fit oyer IIOlI>!lthing. _ Sucb a part \IOuld 00 d:U::eDl!io~ fro1!1 inside surfaO$ to il:IJ:ide oorl'lWG •. 'fil1ll is oalled 1m "i=id& diDerudon".

F/86

- p ;.

AERO 330

BEND TANGENT---.... LINE, BENDING STARTS AT THIS POINT.

A

331

T

MOLD LINE l--BTLD -...,1

1->---- MLD -----<>I

A

~ BTLD

I.:

B .

.. +. BA + ',- '. ,', . DW

DIMENSIONS OF A BEND

FIGURE-4

C

BTLD

Developed Yi~th (Dw)

PAI3E 3-8

The "developed vidthR i8 the vidth of material required, lO&al!lt1red around the bends from edge to edge, Finding the developed vidth vill ansver 0= first problem, which 111 exactly what sise to cut the stock. The developed vidth will be less than the I!llIn of mold 11M dimensions lIillce the metal is bent on a. radius a.nd not to a equare corner as lIlOld line dimenllions indicate.

I

F/86 AERO 330 331 PAGE 3-9

A simple axiom \Thich can be spplied to finding developed vidth iSI liThe \Thole of anything is equal to the Blll!l of its partsn • Referring to Figure 4, DW = A + B + c.

Bend All(l'.lance (RA)

To find 'the developed \Tidth of a part it is necessary to knC1J the flat distance or uallwance" of the metal vhich vill be curved in bending. The term. referring to this sec::tion of metal vithin the bend is llbend elJ.ovance". -The bend allovance may be considered as being the length of the curved portion of the neutrel line. Sec­tion B, in Figure 4, is the bend allmianc::e distance. The B\llIl of this bend allml­ance distance and the length of the unbent sections vill give the developed vidth, as shoJn in Figure 4.

The bend a1.lmlance required can be accurately and easily found by the use of a band allovance chart. The bend allovance chart, Figore 14, lists the allmlance in inches per degree of bend. To use this chart, find the a1.lmIanc::e under metal thickness (T) and opposite the radius (R), then multiply this number by the given degrees of bend.

Exmnplel Using the chart, find the BAfor a 90" bend in .032- material on a 1/8" radius.

Step 1. At the junction of the column under .032 and in the line opposite 1/8" bind the elJ.o\lanc::e 0.00243. This is the RA in inches per degree of bend.

Step 2. For a 900 bend multiply .00243 by 90 •

• 00243 x 90

.21870

The a.ll.ovance" tor this bend is .2187". Using!;. decilnal equivalent chart it may be changed to 7/32".

The bend ailm;ance chart lias developed from the bend allollance formula. This formula is called an empirica.l formula because it vas arrived at by experiment­ation rather than by aIrY precise calc::ulation. The empirical fOnmlla for bend al1croH1nce iSI

BA = (.01743 x R) + (.0078 x T) x the number of degrees of the bend.

This formula is seldom used since charts are generally availabls. As a matter of interest, the formnla \la!! derived by taking into account the length of a 10

arc on a given radius. It has been found. that .01743 x R best represents the length of a 10 arc. The formula also COIlBideres the radius required to reach the neutral line of the lIIetal. This vill vary \lith the thiclmess. The second empirical value of the bend allovance formula, which corrects for the radius required to reach the neutral line, is .0078 x T.

F/86 AERO 330 331 PAI"E 3-10

S8tba.ek (SB)

To find tJ:w DW of a part uaing BA, \Ie must have the bend tangent line dimen­sions to whioh are added the bend allowance for each bend. '1'0 find the bend tangent line dilll9naiona when IIlOld line dimensions only are given, as is often the oase, it ill necessary to subtraot a di stanca oalled ft setbaok" from each lIXJId line dilnension. Setback is the dietance from the bend tangent line to the mId point. \./ben a part has IrOM! than one bend, setback III!lst be subtracted for eaoh bend. The majority of benda in ehefltmetal are 9{l0 bends. Sotbaok for all 90° bends is equa.l to the sum of the ln9tal thicknBBB plus the radiua of the bend, ILB shown in Figure 5. The folloving formula iB used to find. the EnD for a part vith one 9{l0 bend when IIlOld line diD:enaione only are given,

BTLD = lIALD - 59

I~'-t-I----'I ---.. SETBACKf.-BiLD~

1-0--- M L 0 ---oj FIGURE-5

I

F/86 AERO 330 331 PAGE 3-11

\/ben the tanos ueed in layout \/Ork are olearly mrlerstood, ms.ka a. flat layout of the ohannel seotion illustrated in Figure 6.

A

CHANNEL SECTION

FIRST STE:P

SEOOND STEP

B

END VIEW OF CHANNEL

FIGURE-6

THIRD STEP Find the dEl"leloped width. Looldng at the end rlev of crar chan-ne 1 , Figure bE, we BJJ:y divide the I!III tal into bem tangent line

and bend allo\l!UlOEl diBtalloos. Dimensions A, C e.nd t are bend tangent liM diJlleneions. Sections B a.nd D have /I. flat width, before bending, equal to the bend tI.:l!'!.ovs.=e. The developed vidth (DY) will be equal to the length of eection A. + B + C + D + E. The .tepa in finding the dOTe loped width of _ thill ohanne1 are I .

1. Determina and IIrl. te dovn for fnture reference the Betback a.nd the be nd a.1lo\l!Uloo.

Satba.cJ:: for a 90' 0000 is Iilqwil to 'f + R or .051 + .lB7 = .238"

Bend a.1lollB.IlCe for .051 _taria.l on Ii 3/16" raditlB is found 1'ro!;t the bend a.llovanoe chut to be .OO367R per degree.

I

F/86 AERO 330 331 PAGE ':'-12

2. Find the 'Jidth of section A, the BTID of one flange of the channel:

.A = 2" - SB

kny decimal dimension 'Jhich must be transferred to the metal 'Jill have to be converted to the nearest 64th common fraction if a fractional rule is ll.'3ed. The finding of developed 'Jidth, hO'Jever, is normally done by a calculation on paper so it is best to add each section as a decimal and than convert to a common fraction 'Jhen the final anS'Jer is determined.

3. Find the bend allOW'ance, section B:

B = .00367" x 900 or .330"

4. Find section C, the 'Jeb of the channel:

C = 4" - (2 x SB). Note that twice the setback must be BUbtracted for the BTID of a 'Jeb.

C = 4.000" - (2 x .238) or 4.000" - .476' = 3.524"

5. Find section D, a bend allOW'ance dimension:

D = .330" the same as aection B.

6. Find section E, the BTID of the second flange:

E = 1.762", the same as section A.

7. No", DW = 1.762" + .330" + 3.524" + .330R + 1.762"

DW ~ 7.708" or 7 45(64". We nOW' knOW' hOW' \lide to cut the stock.

F',G!;:T -;~i~::';': '-"~'fe? the layout to the metal. IT only one piece is needed a layuut can -be made directly on the material provided that·no scribe

or punch marks remain on the finished part. A scriber may al\leys be used, for accuracy, \lhen marking cutting lines. However, other reference lines should be made "ith a soft lead pencil to avoid surface scratches. 'When a lead pencD .. is used, it should be sharp and an allOllaDce of 1(64" should be deducted for the vidth of the lead in all measurements.

- P' ; . .. hen several pieces are required, a template may be made for quickly duplicating the layout. Normally a template "ill be more accurate than a layout on the actu­al stock since a scriber and divider can be used for all lines. For this ezrunple, hOlJever, let us eS6Ulne that the layout is to be made on the stock itself.

1. Secure the stock. Be sure it is of the specified material and of eufficient aize.

2. Shear a strip to 6". the channel length.

F/86 AERO 330 331

:3. Check one end for straightness and mquarenesB. This beoomes the reference Itdge. 80. Figure 7.

4. Sot a eol!lhinat10n IIquan at 7-45/64", the developM vidth. UIrl:ng it agaiIlllt the refarenoe edge, scribe the cutting ooge.

5. Bend tangent lines \lere neosB8lU7 in our paper ealeul.atioIlll to arrive at the developed vidth. Howver, they vill not be n&eded on the metal. '!'be ILDSIIer to the 5&0000 problem, vbere to bend, can be had by finding the "brake reference line". This vill enable u.s to properl;r poll1tion the metal in a eornice brakB for bending. This layout vill be complete e.nd fabrication oan begin wen 110 have made a line for /llhearing and two brake reference lines for bending.

3/1&" 3/18'" .. -,-

ILl

s-s

I II:

[ [

.... ~BRAKE :~ -"

REFERENCE

'.

I I 3.524- ----1.-01.:1 +1.7sj. ~--------------------7~·~-------------------------~

FLAT LAYOUT OF CHANNEL F'IGURE-7

ILl

g ( ILl

'" z ) F !; ( u (

) < }

PAGE :3-13

/

Before go 1ng IIl.b.s ad ,.." should tau t1E>s to 8 tOOy the de tails 0 f 0= beDding r lU.Chine, the cornioo br<Lke. in order to cllU1.rl;r understand the location of

l-_~~~~re~f~e~re~n~c!e~1~1~n~e~s~m~~~~the~~be~~~!0~er~a~t~io~B_i~t~~~lf~. __________________________ = •

,\

, " "

" .:- .)

'. ,~ I::' ':' . \:~'.!I ";' '1

. ~

"(. I~ ." ", I ~ \'

"~i·~;" / .~ • ,II

I

"I

"

....,/'..

J '.

~ ,\

..... ' . j

BENDING LEAF

\

CLAMPING BAR

..-cLAMPING BAR HANDLE

CORNICE BRAKE FIGURE-8

COUNTERWEIGHT ~

- . ~ V~'~

~CLAMPING BAR ADJUSTING SCREW

---t:ccENTRIC ADJUSTMENf SCREW

IC ADJUSTING LOCK SCREW

"-RFNnING LEAF STOP

'01 "­OJ o

D rn ;U o u) ((I o

(0 ( , .U f."

-v J) e, m IJ.' I

.t>

F/86 AERO 330 331 PAGE 3-15

In order to function properly the cornice brake must be adjusted. for the thickness of material being bent.

1. CIBlllping bar adjustment

The distance from the nose of the brake to the edge of the bend I!IUBt be equal to the thickness of the material. AdjU.9ting screws are provided. at each end of the upper clamping her for this p12IpOse.

This is an important adjustmentl If this distance is IIDJ.ch less than T, excessive pressure "ill be applied. "hich can damage either the metal or the brake itself. If the distaDce is :rwre than T, the radius of bend "ill be increased.

2. Eccentric adjU.9tment

An even presBUre IIDJ.St be applied to clamp the metal being bent. To provide for pressure throughout the "idth"of metal in the brake and also insure that the eccentrics "ill go Rover center", there are adjustments in each clamping handle.

A bending leaf stop consisting of a rod and collar is located at the right side of the bed. This provides for duplicating angles of bend. When the collar is set it '\lill llmi t travel of the bending leaf to the proper degree.

F/86

- ..

T

PIVOT POI~T

BENDING LEAF --+I",

AERO 330 331 PH(;'E 3-1 c.

f..---------DISTANCE EQUAL TO"TH

J--------EQUAL TO RADIUS

>...--- BRAKE REFERENCE LINE

CLAMPING BAR

POSITIONING METAL IN A BRAKE FIGURE-9

F/86 AERO 330 331

locate the bral;e reference line and bend the part.

Fig'ure 9 illWltrates a cross seotion of a cornice brake lilt the point where the metal 18 claEped for betrling. The noBe of the brake clamping bar lIiUst have the proper radiu!! for the lDBtal that 15 to be bent. SeIDe braDS have

PAGE 3-17

a rel!Ovable c1eEping bar DOse that may be chang&d for different radii, other type s have a fixed radius.

If the radius of the brake happens to be smaller than the I!linimnm required for the metal being bent, and cannot be changed conveniently, the nolle of the brake may be shimmed to the desired radius by bending a piece of IDetal around the DOlle and clamping. ~ Figure 10.

SHI M TO GIVE DESIRED RADIUS OF BRAKE------,

I I T- f'C­

I I I I I

FIGURE 10

The brakB must nov be readjUf!t.ed for the thickness of the metal being bent.

f5..s"t.(ii-·1: .... - ~;,;.i.; :~'Jrit"··-;n~~ n-·'t;.;J~· .. rLi:-~'.-::; b"~,:.k.-s·ys.E'-~ .~;::: ?=l!r:tl::;.1oM'~~ ;::1.~\ tbe'::brm.ke so. that. the bend Yill start at one bend tangent. line and end at ·t.ha oUler. \/hen the metal 15 clamped in the brake end bent, the bend Yill etart baek under t.be DOl'le II. distance exactly equa.l to the radius of the nose. One bend tangent line should coincide Yith this point. Since thia point is hidden under the nose of the brake, II. sighting or reference line is needed to properly position the _tal for bending. This l1ns, called the "hrlll.ka refarenoe line", is loca­te<! at 'a distance equal 1:.0 the rM1ua of the brnm J.1!eMUred ouWyd fro]!! the bend t.a.nge n t line be ne" th the c l.e.lnp ing bar. Seo Figure 9.

ThiB distance can most conveniently be calcttJ.Ated end mea.sured from the edge of tho _tal.

I The bram referenCB dimension in our CIlUlliple 16 equal to B'l'Ul, .!". 1.762 I plus the radiUf! .187 or 1.949, changed to the nearest COlil!ll:m frCllCtion, 13Q Q

___ l_-6 __ l/ __ 64 __ ' __ BO ___ th __ a_t __ i_t_c_an ___ ~ ___ l_O_C_a_ted ____ on __ th __ e __ me __ tal ____ by ___ ~ __ a_snr __ ing ___ • ______________________ --__

F/8<o AERO 330 331 PAGE 3-18

'rue _tal is placed in the brake for bending eo that this rafertlncs line is ro:a.ctly even vit.h tile nose of the brake. This can be sighted by eye from

- directly above, or measured. Arre\lS are often marked on the mUll to sho\l in vhich direction it must be placed into the brake. !leo, it ie oometims importam:. t.o decide the order in vhich bends are to be made. Usually the bending leaf' will have to be carried a little past the desired degree of' bend to allO\l for springback of the _tal.

If the layout i15 C81"ef'ully dODe and the bends properly made the finished part should bold to the spec1rled dimensions. Apply the theory discussed thus far by doing 'the follo\ling practice problems. !Devera will be fooni on the last page of tile text.

!. Find the bend allo\lB.DCe for each of the following benda:

1. ! 1° bend in .064" _terisl on a 1/4" radius.

2. A 90° bend in • 032" material on a l/S" radiU3 •

3. A 90° bend in • 051" material on a 3/16" radius •

4. A 90° bero in • 081" material on a 5/16" radius •

B. Find the developed width of the following sections:

ID " ~

. " .~5t'.32 R.' , . / '. -. . I ' }(f' '. -.L

_ I 3/4~fO-

T 314-

I. 2. - .... ~ FIGURE-II

,. :; ..

F/86 AERO 330 33~ PAGE 3-19

In some situations sheetmetal men may work for long periods of tilDe withont being required to perfoI'm layout calculations. In others, bend layout may be a very COmIron part of the job. The tolerance may be such that parts can be bent closely enough \dthout going through all the layout steps. However, when channels or brackets l!!Ust fit between other members or when holes or cutouts J!!I.lst match, the layout must be made with great accuracy. Thus, the ability to make a good layout is an important part of all-around trarle knoyledge.

Makinr a layout of Open and Closed Angle Bends

To make a fiat layout of fonoad sbeetmetel parts it is necessary to locate where to cut, where to drill end where to bend. Cutting lines will normally fall along the developed \ddth or lengtb. Regardless of the angle of bend, developed \ddth is equal to the sum of the bend tangent line dimensions and the bend s.llo',!ance distances. If we are to deduct setback from a given mold line dimension in order to get a bend line dinension, we I!lU5t first kno',! ho',! to find the setback. When the bends concerned are of 90°, the setback for each side is equal to the sum of the netal thickness and the radius. For bends of other than 90°, Buch as the open

B

.58

f-c---nLD

OPEN A/'I6LE CL05ED ANGLE

. FIGURE-I

C4r!r;le A is les5 than ')Go) or closed (Angle A' is greater thEL'1 ')G") angles illus­trated in Figure 1, the setback distance may be found by applying shop trigunometry or by use of a chart derived by use of trigonometry.

F/86 AERO 330 331 PAGE 3-20

Thia chart, ImOIiI1 as a • Setback Chart" or "K Chart" will eliminate BOrne of the calculations.

It is not frequent that shop trigonometry Yill ba needed for finding band tangent line dimensions aince a K chart ia usually available. Hovever, the principles may be applied to other eitu~tiona in layout york such as when insufficient infor_ mation is given on a print. There are alao various other problems in mechanics .TIera a solution may be reached by setting up a triangle with ~iven !r~ormation

. and finding an unknown side or angle. For these reasons a short discussion of shop trigonometry is included aa an appendix to this section.

The problems which follov illustrate methods of making flat layouts for parts which have bends of other than 90°.

Problem 1: Layout a template for a closed angle clip.

b=TLlJ

/i. ---'--1 4

/

PERPEfYDICULllJ2 eEFE.e£HCE LINE

~ V

-J

-2

--------

A

-4 -5

!

-3

-6

! ! -. - . -.-~a ( L v -;;e, -Ie .• l.il:~1

B

FIGURE-2

Procedure: 1. Study the drawing, Figure 2A.

2. Take metal of proper sire for the part.

'"

B

f /

) 1 "--REFCK'ENCc

EOGE

I 3. Shear a straight edge. Thie is the reference edge illustrated

in Figure 2B.

-------'

F/86 AERO 330 331

4. Scribe a perpendicular reference line, -1, near one end. (Metal may be sheared on this line.) .

5. Set a combination square for 1" vidth and mark locations near each end, such as at -2 and -3. Carefully connect these marks \lith a straight edge.

6. Next locate and scribe the bend tangent lines -4 and -5, the cutting line -6 and a brake reference line.

In .:>roer to locate the lines noted in step 6, ve must find the 8IlEJWers to the following questions. Referring to Figure 2A:

a. How much should be subtracted from Ii" to find the BTlD7 From 7/8"7

b. What will the bend alloYallce be?

c. What will the developed length be?

d. Where should the brake reference line be?

PHt~E 3-:21

First, it is desirable to determine by calculation the bend allowance and the setback and to recoro these reference distances. In tne u!SUB.l manner, find bend lilo.mnce from the chart. For.064 material on a 3/16 radius, the bend allo\laDce lor 1° of bend is .00377; this multiplied by noo of bend equals .415 or 27/64. No", look at the setback chart, Figure 23. The value K, f'rolll the chart, is a constant for that degree of bend. As indicated, the setback = K (T-IR). ThiCkoSBS

(T) and radius (R) are variable and must be determined from the speCifications for the part. Note that K for 90° is 1, therefore, the setback for 90° = I (T + R). The !!etback for anv degree of bend other than 90° is not equal to 1 (T + R) •

To find the BTLD represented by "An in Figure 2B, refer to the setback chart. In the column under AO, find 110. Under K read the ccnetant, which is 1.4281. TIsing the formula SB = K (T-IR), IJUbstitute the koown values; T = .064 and R = 3/1-6 = .1875. Then, solve as follo"s: .

SB = 1.~281. (.06!, = 018:75)

= 1.4281 x .2515

= .359 (to the nearest thousandth)

The bend tangent line dimension, A, will be

- .. 1.250 - .359 = .891 = 57/64

To begin the actuaJ. layout on the material, l!Ieasure 57/64" from the perpendicular eferenee line and mark line -4 (a bend tangent line) as shown in Figure 3.

MBaSUXE! 27/64 from line -4 and mark line -5, the bend allo"ance distance. This is ur second bend tangent line. We have no" progressed around the bend to the

straight eection of the flange. 'To find BTU> "C" (Figure 2) subtract the previous­ly determined setback from the lIlOld line dimsnsion _7/8n

•

F/86 AERO 330 331

-I -7 f/t--- 1 '-R,QP/U.:!>

t <> , -4

, -5 It

/ " % 1:1

\jJ '<l

~ U+33 <{;". - ·(.4 b 4- ...

/5:3 (;4

PE/ZPENP/CULAI. .eErERENC£ LINE

-(;

FIGURE-3

7/8 - 23/64 = 33/64"

.875 - .359 = .. 516"

-3

~R.~FEeE

PAGE 3-22

NeE

Measure and mark line -6. This line completes the developed width and locates the cutting line.

The brake reference line dimension can then be found by edGing the radius distance to the BTlD of the flange which will be under the clamping bar.

Brake Reference Line Dimension = BTLD + R

= 57/64+ ]2/64

= 69/64

= 1 5/64

Measure and mark line -7, the brake reference.

- ~rill a No. 40 hole near each end of the brake reference line. Using a transfer punch, mark the location on the stock. Draw arrows from these holes to indicate the direction that the material 1s to be inserted 1n the brake. When making a small part of this type, it is beet to put the longer flange or "leg" in the brake eo as to have a greater clamping area. Cut out the template and file the edges

) accurately to the scribe lines.

Label the template wit.h all pertinent data. (The dash numbers are u,"ed in this text as an aid to understanding and would not be used on an actual layout.)

PAGE 3-23 F/B6 AERO 330 331

-,..-----------------------------i( $ws-m-' I.

--------

(A) FIGURE-4

Problem 2: Layout a template for an open angle clip.

Procedure:

The part illustrated in FiguNl 4 is a reinforcing clip bent up to fiJo. Secure suitable ~e~l ~d shpar the reference edge. Mark lines -1, -2 and -J as ~hovn in Figure 5. Reforrin~ to Fi~Nl 413, the first layout dimension is distance "a". This is egl,al to the MIll of ltn minus the setback. Set,back is found by Use of the chart. Under AO find 60°. On that line, under "K", read .57735.

Setback = K (T + R) = .57735 x (.064 + .1875)

= .577J5 x .2515

= .1452"

DiJrensi:Jn "a" \.Iill then be 1.250" - .1452" or 1.1048", rounJed off to l' 7/64". Measure and scribe -line -4, a bend tangent.

f2-/~--i \ ? ''1 -3 .;'_~-.'"-~ ~ _~~.'~~_ .. P!.L

-4 <:l -5 _6 '" .. , f

/

~ " J

~-/ I ~ .z 1--1!-'4 32 ,;-

- f'" ;;

FIGURE-S

Nov find th" bend allovnncc. From the chart read value .003"17. This x 60 = .;~;>62 or 7/32". M8aollre and mark bend tangent line -5.

I

F/86 AERO 330 331 PAGE 3-24

The remaining dimension "c" is equal to the ML dimension of 7/8" rr.inus setback or .875 minus .1452 = .7298 or 47/64". Measure and mark line -6.

Measure 3/16" from tho BTL -4, tho line to be placed under the brake clamping bar, and scribe referonce line -7. Drill transfer holes and mark tem!llate \11th &Tro\l to sho'.l '.Ihlch '.lay the metal is to be placed in the brake. Aleo mark the degree of bend. This template layout is no'.l complete.

Problem 3: Make a template for a reinforcing channel section having more than one bend and three holes to be accurately located.

Procedure :

Study the dra'.ling, Figure 6.

Secure metal a!lproximately tOt, x 3". line -1 as sho\ln in Figure 8. Set a Connect these points \lith a straight "A", Fieure 7.

A = HLD - (T + R)

A = .75

A = .75

(.032 + .125)

.157

A = .593 or 19/32"

Shear reference edge and scribe refe,-er.ce square at 2" and mark points -2 and -3. edge. To begin the layout find dilr.ensio~

Measure and scribe bend t~eent line -4.

Find diUl€nsicm "B", '.Ihieh is the bend allo",ance for a 90° bend, '.lith .032 lI'.aterial on a l/il" radius.

BA = .OO2i.3 x c;o = .2187 'or 7/32"

Heasure and scribe ber,d tangent line -5.

The next step is tc;, find ~,ir.cn8ion "e" vhieh ia the straight' ."~ ~ c,f ';~';,'i ;",_' betllcen th" two bellds. Thd BL di.rr.ension is given as 2 3/1.". This includes set­back at each end, ",hieh must 1:>e Bubtracted to find C. On th", 90" end, it ar..ounts to T ?la-s:1. On the 120" end, the setback '.Iill havtl to bs founn from the "K" chart. Und,,!' AO find 120, adjacent to it U!lder K read 1.732. Proceed as befo!'".

Setback = K (T + R) ~ ... ,

= 1.732 (.032 + .125)

= 1.732 x .157

= .2719

Dimension C = 2.75[(1 - (.2719 + .157)

= 2.32ll 0:' 2 21/6/."

I

i ,

1

F/86 AERO 330 331 PAGE .3-25

Measure and scribe bend tangent line -6.

next cOltT]Jute bend ello\ofS.nce, for 120°. Find the value .00243" per degree, .()f)::>4; x 120 = .2916 or IG/64 n, metal required for dilD9nsion D.

Measure and scribe bend tanfent line -7.

Tr.e remainin£ dimension "En ie 2.5 minus .2719 (MID - SE), ~ich equals 2.2281 or 2 15/64". lI",a3=e this and scribe line _8. The overall developed length or BtrBtch out is the sum of these dimensions or 5 43/64". -

No~. ley out ho19s on the flat pattern. Refer to Figure 6. Note that all hole ciiJnf,nsions are given in the srune lIl/lIlIlflr as other layout measurements, that is, to the mold point. ThE' center of the -tn hole in the web is 1 9/32" .from the XP und I" from the edge of the metal. Set square at 1" and drSII line -9, figure 9. From MID 1 9/32, subtract setback, 1.2812 - .2719 = 1.009 or 1". Measure this distance from BTL -6, intersecting line -9 Ilith line -10. Drill #40 hole on center for transfer punch and mark teltT]Jl!tte to indicate finished hole size. A punch mark on the stock is necessary since it provides S center for the drill or hole punch used. NOll scribe S circle on the template to eholl true hole diruneter.

The other tIlo holes in the flange are located in the same lIay. From the given di~nsion subtrsct the setback,

1.5 - .;271Q = 1.2281 = 1 15/64"

Measure this distance from BTL, -7, and scribe line -11. To locate the center of thB t~ ho:es on this line, usa either a square or pair of dividers. Measure distance from ono hole to the edge of metal and scribe line -l~. Scribe line -13, t88 re~u~'Ed distance. Drill transfer punch holes on center, mark template for hole sizes and scribe tru~ di~tAr.

-

l REF_ REF. -/ I ,

I -~'" .~.'~. \ , 4- -5 6- -7 -d

'" !::! rr -13 • ___ -1+ '" '" I- Q '" -10 :::, Q

~ -9 ~ c"v -15 -/1

2_l ) :::. I-Cl \.;

~p,eILLi III I

< NO·1 #0.2 .... I 'll ,; -,/2

ORILL#IOJ I t 2 HOLe::. --L L

-, I-c! 1- -i !ff I -/ -f ----1 FIGURE-9~ I

I

3

F/86 AERO 330 331 PAGE 3-26

iii! (rY'P)

1-----2~

I

9 1----/ .32--

A , \I \I II II II II II

~-4:~ 8~~1=. ========~ iii

2 I I

I z I

FIGURE-7

"f DR-ILL FIGURE-6 - Z HOLJ!!:J

1--, ---------------~2~------------~·1 ~! -,

-2 -.3

-r-

f--.---4 -5 -G -7 -ll

3

~ .. ;

2 - -

I . 1-,

2" \ .. 221 ~~ 2 15 l-o'-l9 C4-(;.4- '4 32 ~.3Z

F/86 AERO 330 331 PAGE 3-27

Now, brake reference linea ahould be located. Carefully determine Which bend lInlJ'It be lIIAde first. If the 2t' leg ill bent first, it \/ill IIt.rikB the bre.ka ..men the 90°, 3/4" flange ia bent. To avoid this, elide the mtal into the brake arrl bend up the 3/4" flange first. Sin~ the radillll ill l/B". the referenoe liM should be lOOasured 1/B" !'rom the BTL (-5) and from line -14.

Drill transfer punch holes, mark =I./S, and designate as No. 1 bend. A.ft.er the first bend is l!!Brle the metal is ra leaeed and moved in the brake (tovard the oper­ator) until the ooc:ond reference line ia in position. This line, -15, should be lOOarured liB" !'rom BTL -7. It if! scribed, marked \lith the degree of bend and arrel./B and designated 8.S No.2 bend.

This completel'l the layout. 'rhe template l!lhould nol./ be labeled, caref'ully cut and fil&d to exact eize. It is then ready for nee in producing the pa.rta required.

Problem 4: Layout a template for a part having a bend not parallel to the edge.

Procedure :

Some sheetmetal parts have bends lIhich are not parallel to the edge or benda 'Jbich are not parallel to each other. An example of such a part ie the COIIllIlOn wing rib.

Tha reinforcing clip shovn in Figure 10 bas a bend not parallel to the &dga. 'l'he layout procedure for this olip requires that a I!!9ld liM be located on the pattern. All other layout lines are made either parallel or perpendicular to thiB lIlOld line. In Figure 11 the I!!9ld line paslO8s through I!!9ld pointe at I" and 2" from the refer­ence end.

SGcru"e E1.v.j:t'i~:J.-"-'i-rl0.r:'l"":: ·;:.ha..n·-ff~: J/E.r;,~ C~.t.·:.13. rs!'Sl"eDCS-- -an1 exd eheck for atrrlghtneaa o

Scribe line -I, II osid", parpendioular to the reference end. Locat& a point on thill

line !I. t MLD 2" •

Scribe line ...2, the second lIide, perpendicular to the reference end and 2 l/B" to the right of line -1. Locate a point on thie line at MID 1".

IIi th .... IIharp scriber dray the mId line, line -3, connecting the t'olO mold points.

locate bend tangent line -4 by lD9asuring back T + R or 5/32" D.II II perpendicular distance from the mold line. Scribe this line.

Z

F/86 AERO 330 331 PAGE 3-28

r:f=:i -.;;

<ge-t-}-.q

"Y""" e", _ -v;>-o .:>: ,: / -v,

-" C Gc ""r

T 2 <-<Ve- ....,.

.1.R -/ / Ci

1 I • zl.. .03Z.-lf-- REF . .:5 END

FIGURE-IO FIGURE-II

Find the required bend alloIJance. For this bend it ia 7/32". Measure and draIJ bend tangent line -5.

NOIJ, locate the points for a line draIJD at -@A wich Yill intereed linea -1 and ~.

From theae points scribe linea -7 and -8, the aides of the flange, making them perpendicular to the iBA Una. (-bEA ia the center of tile bend.)

'!'he end of tile flange, line -6, Yill be parallel to bend tangent line, -5, and be located at 3/4" - (T + R) or 19/32" from it. Measure and scribe line -6.

Locate tile bre..ke reference line in the u8118.1 manIlBr by measuring (into tile bend) one radius from the bend tangent line wich ia to be put =der the brake. This line has been left off for clarity in Figure 11.

US" of the "J" .Chart ~ .. . .:..;.:;".

All bends in sheetrnetal can be laid out by the use of bend allolJanc<3, as ~iBcussed thus far • .A second method for maJdng layouts of bends employing a eomewat differ­ent principle may also be U!led. This requires a "J" Chart.

'!'he "J" Chart method is lees accurate tilan the bend alloIJance method, as so:ntJ .l'VOr usually ente.rs in IJhen reading tile chart. Also, tile reference lines for locating metal in a cornice brake wen making open and closed angle bende cannot be determined Yitilout finding bend tangent linea using the "K" Ch-'irt end the rend allcvance me thoe!. The" J" Chart method does, hovever, enable a mechanic to \!!B.ke bends from mold line dimensions without finding bend allownace.