Illustrated Sourcebook of Mechanical Components Part 10 potx

tion p=zero the snap-in force is related to the spring rate of the snap by the tangent of the lead angles and the interference see accompanying cantilever drawing as an example.. Spring

Fastening &Joining 20-2 1

1 2Fused glass

i

~d

Saled-beam lamp has t h i n flexible metal

cap fused t o glass

Metailized edge o f glass window is'

11 soldered to flexible metal frame

tal -qap soldered 'to large-area dtglhsg surface * 1

> * " + $

Simplifying Assemblies

Since annealed spring steel can be stamped, twisted, or bent into any desirable shape and then heat-treated to develop spring characteristics, it can be designed for multiple

Arched prongs

Pre-locked position

FIG 1-Multiple-purpose flat spring has stamped hole

helically formed to accept adjusting screw Replaces a

locknut, bushing with internal threads and spring blade

Screw adjusts gap of contacts thus changing duration of

current flow Application: thermostatic timing control

unit of an automatic beverage percolator

FIG 2-Spring-steel clip firmly holds stud of control knob

while allowing it to turn freely on its bearing surface

Clip is removed by merely compressing spring arms and

pulling off stud Replaces screw and machined plate

FIG 3-Floating clip, which snaps in place by hand, re-

duces hole misalignment problems by permitting sufficient

shift of mounting holes to offset normal manufacturing

tolerances of main parts Replaces welded T-shape nuts

F k 4-Twin-hole nut removes need for hand wrench in hard-to-reach location and replaces two nuts and lock- washers Combined force of arched prongs and base when nut is compressed creates high resistance to vibration loosening Application: gas burner assembly of an auto- matic household clothes dryer heating unit

FIG 5-Push-on nuts ( A ) easily press over studs, rivets, tubing and other unthreaded parts Their steel prongs se- curely bite into smooth surfaces under load Application:

FIG "Previous method of assembling desk calendar

( A ) required seven parts: wire guide, spring clip, plate,

two bolts and two nuts Multi-purpose spring clip ( B )

replaces above although using same retaining principle

Fastening &Joining 20-23

compensate for hole or part misalignment; prevent vibration loosening;

eliminate parts; speed assembly; permit fastener removals; tock on

unthreaded studs; and permit blind installations

FIG 7-Expansion-type fastener permits blind installation

where access is from one side of an assembly only Inser-

tion of screw ( A ) spreads fastener arms apart thus pro-

ducing a wedging effect in the hole Dart-type fastener

(B) can be quickly snapped in place; one common appli-

cation is attaching molding trim strips to auto panels

FIG &End clips pressed by hand on panel edges have

barbed retaining leg which either bites into the metal or

snaps into a mounting hole Applications: ( A ) sheet

metal screw and J-clip with arched prongs compresses

insulating material between panels; ( B ) bent leg of clip

acts as spacer between two panels to support sheet of

insulating material; ( C ) barbed-leg-clip retains wires without need for mounting hole; ( D ) S-clip spring-steel fastener secures removable panel i n inaccessible position FIG 9-Tubular-type fastener has cam-like prongs which spring out after insertion to hold fastener i n position Applications: ( A ) radio dial pulley; ( B ) attaching auto- motive name plate to panel

FIG 10-Special-function fasteners for quick assembly and disassembly of components ( A ) Wire harness clamp using torque and slot principle; ( B ) dart-shaped clip for

attaching coils and other parts to electronic chassis

Spring-Steel Fasteners

Future articles will cover cold-formed and quick-operating

fasteners, plus new fastening ideas

Spring-steel fasteners are versatile and low

in cost The steel is bent, twisted, and

pierced, sheared and drawn into almost

any desired shape to form a one-piece

fastener that combines the functions of

several ordinary fastening components,

reducing fastening costs

steel fasteners and are particularly useful

as light-duty fasteners They are self-re-

taining units, needing only a hole, flange

or panel edge to clip to Their inherent

springiness makes them resistant to loosen- ing by vibration, and tolerant of tolerance buildup and misalignment

The field of application of spring clips

is a broad one, including automobiles, home appliances, hi-fi and electronic equipment, toys, aircraft and office equip- ment

Dart type spring clips (Fig 1) have

hips that engage within a hole to fasten two sheets or panels Dart clips are popular for fastening printed-circuit boards and

Stud-gripper spring clips (Fig 2) are

designed to grip unthreaded studs, pins, rivets and tubes The studs can be of circular cross section, as is usually the case,

or of square or D cross section Generally, the stud gripper has two or more prongs that permit the clip to be forced down on a stud Such grippers resist removal Any back pressure against the clip causes the prong.to bite deeper into the stud

Some stud grippers use a split tubular sleeve to grip the unthreaded stud or rivet Such clips provide a secure lock, yet allow panels to be separated for service Cap push-on stud grippers are used on

Circuit component

Door seal

- For round or

D-shaped studs

For hardened round studs only

-,,

U-clips

D-clips

Quickly installed, they eliminate the need

for special machining or threading opera-

tions or cotter keys

signed to grip into a hole or plate, or retain

a wire or tube They can be employed on

existing parts and assemblies without a

design change

U-shape clips are used for assembling

cover panels or as inexpensive hinge re-

tainers s-shape clip scan clamp onto a part

while clamping a panel or a flange of B

component C-shape clips provide a com-

pression action that can hold plastic knobs

be easily removed

Spring-steel nuts (Fig 4) ace single-

thread engaging locknuts stamped into various convenient shapes Available de- signs include flat, arched-back nuts; W-

shape nuts with turned-up ends; self-re- tained, self-locking nuts; single-thread nuts for use in cavities; high-torque nuts with out-of-phase threads to increase vi- bration resistance; and nuts that cut their own threads into diecast metal or molded plastic studs

Some spring-steel locknuts have threads

in which the thread-engaging portion is

pitch of the screw thread These nuts have straight sides and hexagonal shapes for

easy handling and positive rundown Also

useful are spring nuts designed to retain

a shiftable nut to provide rivetless reten- tion of nuts on plates (Fig 5)

Regular locknut Washer locknut

5 Clip-on nuts and nut retainers

Flat round pushnut Removable pushnut

W Clip-on nut retainer

Fastening 8t Joining 20-27

Snap Fasteners

for Polyethylene Parts

cost of separate fasteners with these snap-together designs

the mold than the ejector-pin snap The best length for this snap is '4 to % in

f o r d i f f e r e n t PL

snap Ejected with the pin, the part is slid off

the pin by the operator

fem?le snop

As /orqe as

possiLVe - to reduce tearing

or permonent

vent this snap from working loose, four small

ramps ate added to the female part

mold and on the ability of the polyethylene

to deform and then spring back on ejettion

Plastic Snap-Fit Design Interlocks

Snap-on caps and latches are deceptively simple, but were evolved using good

engineering design Here’s a recent study

In response to the often-heard suggestion

that snap fits are not dependable because

they have a tendency to pop out, Dr

William W Chow of the University of

Illinois in Urbana has developed (and

presented in an ASME paper) an analytic

method for predicting snap-in and snap-

out forces His conclusion is that a well-

designed snap fit cannot be easily pulled

out, and has certain advantages over other

methods

For example, a screw fit can vibrate

loose, a press fit depends on friction and

strain to hold, and a sonic weld is per-

manent

The snap tit is a simple mechanical

interlock whose pull-out force can be hun-

dreds of times larger than the push-in

force It takes careful selection of the slope

of the bevel on both the entering lip and

the withdrawal lip The extreme is a cap

or latch that snaps on easily, but locks on

permanently-like a fish hook

We asked Chow how he solved the

design problems He said he first examined

the simplest case of a cantilever-type snap

with zero friction Next, the same snap was

analyzed with the effect of friction The

results then were generalized to cover all

kinds of snaps

tion (p=zero) the snap-in force is related

to the spring rate of the snap by the tangent

of the lead angles and the interference (see

accompanying cantilever drawing as an

example)

With zero friction, snap-in force Fi =

F, tana, or K i tana Snap-out force Fo

= F, tan 8, or K i tanp, where:

p = coefficient of friction

F, = snap force, the force that reduces

K = spring rate of the snap

a = lead angle

p = return angle

i to zero

i = interference

The smaller the lead angle, the easier it

is to assemble the snap The smaller the

return angle, the less force is needed to

disassemble the snap When the return

angle is 90 deg, the snap is self-locking

When the return angle is greater than 90

deg, the interference is a barb

With friction, the tangent term becomes

a more complex function of the lead angle,

a, and the coefficient of friction, p:

The analysis also applies to hollow cylinder snaps and distortion snaps, but the spring rate has to be figured according-

ly Spring rate of a snap is defined as the

snap force, F, that is required to reduce

the interference to zero, divided by the interference The spring rate for a hollow cylinder snan is the total force in the

Force Fi = 6, (sin + p ‘Os

calculation techniques The example worked out is for simple cantilever

Fastening & Joining 20-29

interference at the bump, [bump:

F,

'rod

&is, = 3i;b

Snap-in snap-out forces The next

snaps The distortion-type lid is a variation

of the hollow cylinder snap, and mates

with a smaller cylinder with three bumps

The spring rate, Kdis, is three times the

force at each bump, Fb, divided by the

drawing shows examples of cylindrical ibump

The product of K and i gives the snap force, and the product of the snap force and the tangent of the lead angles gives the snap-in and snap-out forces

Return angle Cover or latch

Pivot point or hinge

antilever design with hinge is simplest configuration for mathematical analysis

Typical snap-in and snap-out forces are

in the range of 2.5 to 250 Newtons (about

0.50 to 55 Ib) Interferences are usually between 0.25 to 2.5 mm (about 0.010 to

0.100 in.) If: the coefficient of friction is

0.15; the lead angle is 30 deg; the in- terference is 1 mm; and the spring rate is

5000 N/m; then the equation shows that snap-in force is 3.98 Newtons

The table lists some approximate spring rates for three simplified spring geome- tries: a uniform cantilever; a tapered can- tilever; and a thin-walled hollow cylinder

Referring to the free body drawing of the cantilever: force acting at the in-

terference consists of a normal component,

F,,, and a tangent component, Ff(friction) Since all the forces meet at one point, the summation of moments and forces equals zero: M = 0; and F = F,, + Fs + F, +

Fi = snap-in force

F, = snap force, the force needed to

F,, = normal force at the interference

FJ = friction force at the interference

And, if friction is considered negligible, Fi

= F, tan a; and F, = F, tan p

Widely applicable Snap fits for

plastic are common in closures for fill

pipes, bottles, container walls, and other applications where positive closure is needed but tools aren't readily available Cap and plug manufacturers such as Caplugs/Protective Closures (Buffalo,

N.Y.), Niagara Plastics (Erie, Pa.), Clover (Tonawanda, N.Y.), Sinclair & Rush (St Louis, Mo.), and Heyco (Kenilworth, NJ) employ the principles in many prod- ucts they offer

Caplugs, for example, features internal beads in certain of its cap closures, so that they snap into place and hold against vibration J i m Rooney, president of

Niagara Plastics, points out that a popular material is low-density polyethylene

Fasteners that Disconnect Quickly Ideal for linkages, these quick-disconnect designs can simplify installation and

maintenance because no tools are needed

Smoff round-head drive pin could be added to hold sleeve when linkage is

BALL JOINT a n d spring sleeve provide snug

universal motion when hole in center of sleeve

snaps over base diameter of ball Ball diameter

n must always be less than that of the mating arm

Shouldered rod Assembled

easily than conventional cotter pins Although

limited by rod diameter, pin is reusable Light-

duty applications only are recommended

2

I

Assemb /y

ELONGATED FASTENER HEAD and slot can

b e disconnected only when head and slot are

aligned Phase the linkage to avoid alignment

Sih?

Fastening &Joining 20-3 1

W

3

Formed wire retainer I s

eosier to remove

having the freedom of motion of previous de-

sign, are simple a n d inexpensive to make,

Double grooves are usually necessary

bly only when the rod is free to be manipulated

out of the arm Slot design has play, which may

or may not be advantageous

when production quantities are high enough to

warrant tooling costs necessary for clip But

the clip is relatively easy to make

More Quic k-Discon nect Linkages These methods of fastening linkage arms allow them to be disassembled without tools Snap slides, springs, pins, etc, are featured

Ends o f clp pressed

Assembled

PRELOADED FLAT SPRING lets the

connecting rod be adjusted merely by

squeezing the end of the clip together to

remove grip This fastening is not recom-

n mended f o r insulated rods

pressed info linkage arm

w

Assembled

gether make a common fastening method

for many mechanisms It’s sometimes wise

to tie pin to a member so that the pin will

Spring -loaded balls willrecess io permit

pin to go through yoke and linkage

Fastening &Joining 20-33

Ass em b fed

SNAP SLIDE AND GROOVED R 0 6

provide a fastening method with no loose

parts to handle Snap slide is commercially

available, or can be easily fashioned in the

model room

will not allow relative movement between

rod and other linkage member unless the

hoss is free to rotate on its arm

,Boss welded in posi/ion of

can be fasfened for free rotofion

ball-and-socket €reedom combined with the self-lubricating properties of nylon

If load becomes excessive, the nylon will

yield, preventing damage to linkage

8 Dentents for Clevis Mounting

When handles are mounted in clevises they often need to be held in one or

more positions by detents Here are ways to do this

C L M S MACHINED frbm hexagonal Stock-

can be drilted t o receive a bail detent, which acts in Cammed surfaees cast in handle,

able tensioning device, which varies the fol-

lower load Handle can be extruded section

spring characteristic! Piinched holes receive

steel rivet liead which acts a s the detent

mercial “bullet” catch, which detents in the milled internal surface of the clevis flanges

lower, actuated by a spring, which seats

against a pivot pin in the bar and rod handle

WIRE HANDLE acts as spring and foll(rwer

faces and positive stops are made by bending

8 Control Mountings

Frank W Wood JR

or attempts to force shaft too far Washer a t right has two

tabs; one fits in :he panel, the other in the control bushing

Left washer has a boss which fits into a cutout in the panel

and around a pin projecting from the control body

ter Boot seals between shaft and bushing and between bnshing m d

panel With control behind panel rubber grommet seals onlyone piace

HAND-ROOM a t front of the panel

Space knobs at least one inch apart Extend-

ing knob to save space puts it where the oper-

ator can bump into it and bend the shaft

Best rule is to keep shaft as short as possible

rrHOT7r CONTROL KNOBS One ap-

proach is to ground them by installing a brush against the shalt Anlother solution is to isom laie the control by an insulated coupling or a

plastic knob having recessed holding screwsc

I ACCESSIBILITY behind the panel Easy access reduces down time and mainte-

i r -

.!R$Sb?lNb tb-datdhcmtrols to panel

maF$s ,For dud4 adjudtmhnt a Set-Screw

18 Ways to Join Honeycomb Panels

and edge-member attachments

Frank J Filippi & Boris Levenetz

Ever-increasing use of honeycomb-sandwich structures in

many different products, including missiles, has revealed

a lack of basic design information for these structures

The designer’s problem is always: What is the best way

to join panels without sacrificing much of their strength?

There are two basic approaches to joint design: The

pictorial design approach, used extensively; and the analytic

design approach, used less because of lack of time ’Thc

pictorial design procedure is mainly concerned with opti-

mizing one type of structure such as honeycomb sand-

wich Analytic design seeks to achieve the best load trans-

fer at the lightest weight, irrespective of the type of struc-

ture necessary to accomplish the transfer In this digest

the pictorial approach is presentcd In any joint dcsign

however, productibility is the major factor influencing final

selection T h e design engineer must recognize that his

skills are currently at the mercy of the production engi-

neer who must reduce the design to a producihlc article

at a reasonable cost

MID-PANEL JOINT

A mid-panel joint must be designed to carn bending

shear, coniprcssion, and tension loads The shear loads

require connection of the panel corcs, sincc the core is the

only element able to transmit shear forces perpcndicular

to the panel For applications not involving shear loads,

joining thc cores is not mandatory, but is very desirahlc for

joint stabilization T h e ideal joint would have corcs and

faces welded together, providing necessary ties for proper

load transfer It can not, howcvcr, bc produced becausc

of inaccessibility of the core for welding A producible

and analytically satisfactory joint, Fig 1, shows the joint

bcfore the welding operation as prepared for joining ‘Hie

now-accessible core is welded to the web, thc joint is

closed, and a fusion weld picks up the faccs and wcb ’I’hc

addition of the wcb guarantees a good shear joint for thc

core, while the thickened facing compensates for the loss

in strength from the fusion welding operation Although

soine deformation of the core is encountcrcd, good shear

transfcr is still possible

blucli of the brazed hone! comb sandwich manufactiircd

today is niade from precipitation-hardcnable stainlcss

stcels As a result of heat treatment, these steels exhibit

a net growth arcraging 0.004 in pcr in Unfortunatcl!,

thc fact that this growth is ncithcr consistcnt n o r csactly

/

Weldedpriar f a brazing or cbem miNed

Dense core sandwich

prcdictablc results in dinicnsional discrcpancics of the heat-trcated parts Machining a panel edge before weld- ing gives a tncasurc of conipcnsation for erratic growth and should he considered as necessary design practice along

at l a s t two adjacent edges of a n y precipitation-liardcilable steel sandwich

\Vhcrc \vclcling access is from onc side only, the joint

Fastening & Joining 20-39

as the last operation completes the joint

A mechanical joint, admittedly heavier yet, is shown in Fig 3 Essentially a tongue-and-groove joint, the tongue portion is a sandwich bar of densified core, its faces de- signed to carry the longitudinal loads of the panels The bar may be mechanically attached, or brazed in place as shown The mating portion of the joint i s brazed with

a U-channel edge member through which the mechanical

attachment is made

PANEL-RIB JOINT

becomes more cumbersome A solution is presented in

Fig 2 that is satisfactory except for the incumbent weight

penalty The panels are brazed with the edge members

extended beyond the net part size and trimmed to final

The panel-rib joint must maintain the integrity of the original panel and transfer any additional loads, in most cascs a shear-flow, from the rib into the panel, where this load is distributed between both faces Fig 4 shows a

11

13

joint which theoretically would meet these requirements

I'he corrugation transfers the rib loads into the outer

face of the panel and also makes a link between the

honeycomb cores This joint is plainly difficult to pro-

duce because of the accessibility and welding problems

The solution shown in Fig 5 would be easy to make but

extremely inefficient because of the discontinuity of the

faces

The design in Fig 6 meets design requirements and

is producible It is best to make the brazed joint without

the web, then attach it by subsequent welding The panel

then becomes essentially flat, greatly simplifying the braze

fixturing and production sequence The doubler shown

on the drawing may be seamwelded, brazed, or chemically

milled as an integral part of the facing A variation of

this design, Fig 7, shows attachment of a honevcomb

sandwich rib to the panel The U-channel is welded to

both pieces to effect the joint with a minimum of manu-

facturing problems

A mechanical joint, if acceptable for the application, is

quite simple as shown in Fig 8 Thc rib is directly at-

tached to a densified core insert which provides rein-

forcement for the countersink and for the bolt-crushing

forces The doubler between rib flangc and panel provide

better distribution of compression and shear loads

SPAR-PANEL INTERSECTION

llie function of this joint is to transmit shear loads

from the panels into the spar and to assist the spar in

12

14

carrying the bending loads by loading an effective width

of the panel in tension or compression The theoretical

joint in Fig 9 incorporates all necessary elements for

correct load transfer Unfortunately, the unreasonable welding requirements make it almost impossible to produce with current knowledge The production people would prefer to make the joint as shown in Fig 10 The limitation of this design is the inability to satisfactorily vary the spar cross-section as loading changes

A good design is one that incorporates an independently produced spar to which the panels are welded, Fig 11

A shear web is introduced between the sandwich and the spar as prwiouslv discussed before the elements are welded together This layout shows a honevcomb sand- wich spar web riveted to the spar caps with high-shear rivets If welding from one side only is necessary a method similar to one previously described (4) is appli- cable, as shown in Fig 12 The shear transfer is over the short flange of the edge member and cap flange which must have the rigidity to take the shear load in bending The cover plate takes forces only in the plane of the outer facing sheet

Again reverting to a mechanical joint, Fig 1 3 is a

composite of two types of panel connection to the spar

cap The double joint takes all kinds of loads effectively, while the single joint is able to take shear perpendicular

to the panel and loads in the panel of the outer panel facing only Another interesting variation of a mechanical spar joint enables a simplified approach to joining the

Fastening &Joining 20-45

(12)-l'ivotcd Joints Mctliod a t lcft is satic-

factor! for Ion.-cost colislllilcr products t h e r e SOIIIC

I)indiiiq ('all be tolerated i i n t i l the joint tvnrkc i n

'l'hc one ~ I I O \ V I I .;ccond f r o l n tlic lcft is pcrliap

best, because tliere is wine small clearance I)etweei1

the rivet head arid the wall

(13)-Washcrs If a iiictallic wction is to 1)~:

asseiiibled to a wftcr iiiakrial, a washer may bc

necessary to pro\ idc the iiecessary rigidity f o r clincli-

ing actioii 'The soft material should h e outside tvitli

the aaslier rintlcr tlic rivet liead f.'or conventional

a'iscin1,lics eitlicr \ v a ~ is practical

(14)-'I'iglit Joints Sincc hlincl rivets exert c o ~ i -

sicIcm1)Ie gripping force when clinclied, tlic joillt

slio\vii sccoiid froin lcft is inilmctical Coiiverscly

either of cxaiii~ilcs i l l nliicll 3 sirigle rivet is eln-

d may prove :IS satisfactory ax the one with

innltiplc rivets

comlioiients o r sections can be riveted to a base

panel with a siilgle rivet, provided they call bc

niounted from the front, or the base section is ac-

cessible froni tlie rear or nndcrneatli

(Ifj)-Straps and Clanips A blind rivet call lie

used to asseiiil)le straps, clainps, and similar 1ncni-

Iiers aroiind a cc~iiilx)iiciit .\llowaiice must 1)c made

for tlie sqtiecziiig actioii on tlie clamp

(17)-IIoi1sings and Panels , Of the iiiaiiy ways

to construct a horising or panel, the ones shown

here are perhaps tlie most coiiinion Examples: left

-a double-channel scctioii forming thc joint to

which the panels are asseiiibled and riveted; center

-a back-up stringer with a finishing strip inserted

between mating panels; right-a base angle with

riveted panels and a finishing strip between the gap

1 1 1 selecting tlic design, consider cast, appearance,

streiigtli a d thermal expancion

(IS)-Weatlierproof Joints It's difficult to pro-

dricc a pressiirc-tight riveted joiut, 1mt reasonalily-

nioistrire resistant, \veatIier-tiglit assemblies have

lieen evolved

(19)-Extruded Sections Blind riveting is coin-

inon, liecansc of the limited access and clearances in

most extriided sections Iiigidity of the joint at

right is far grcatcr than that at left Setting against

unsupported iiitcrnal projcctioiis is scldoin recoin-

nicnded

(20)-Conipressible Materials Compressible ma-

terials do not provide a firm bnse for the setting

action, a n d tlie rivet m a y tear throogli Use of a

formed slecvr or hnshiiig, or a \rasher and back-up

phte can d u e tks yc~hLe~n

(2l)-'I'iit1iiig Vor iiiasiiiiriiii rigidity, klie rivet

iiicni1)crs 'I'he rivet will set IAind against the cr~rvccl

inlier nall section, or the t u l h g can lie flattened

to increase tlie contact arm

(22)-l'lastie Members l'referahly, the rivet

sliorild be set agaiiist a nictallic rather than a plastic

nieinlxr Ilowcver, tlie rivets are being set siiccess-

fully against iiiany molded and extruded plastic$,

whicli resist setting pressure without cracking

(23)-Blind Iioles or Slots Clinching tht rivet

against tlie side of 3 blind liole or ilkto and against

a milled slot, interscctiiig Iiolc, or internal cavity iq

pos\il)le of the clinching action of the rivct

Sleeve Back-up Washer

Unsotisfoctory Good Good

Unsotisfoctory Good

EX T RUSlO NS

COMPRESSIBLE MATERIALS

Good

BLIND HOLES AND SLOTS

12 Ways to Anchor Heavy Machines

Here's a selection from which to choose

louis Dodge

1, ANCHOR BOLT AND ALTERNATIVE ENDS

f i r s t pour

I

10 ALIGNING JACK AND ANCHOR BOLT

6 ANCHOR BOLT FOR LOCATION ADJUSTMENT

machine frome

3' WEDGE-BLOCK LEVELING

Design Details of

Blind Riveted Joints

Tool Clearance

Clearances and Allowances

tance from a dl or proicction to tlic rivet-liole ccnterlinc i\ critical, should l)c cl~ccked against tool spe(.itications 1)eptli of a cliaiinel o r cylindrical wctinii likewise limits the application if the rii.et

i\ inserted as slioivn Ilowevcr, tool extensions can ofteii be employed, and tlic noscpiece of tlic tool can be extended by as iiriicli as a n inch

(2)-Edge Distance Id’roiii the standpoint of

( 2 ) ( 3 ) joint strength, the recommeiided distance from the

rivet ccnterline to tlie edge of a sheet should not

I x lcts tlian twice tlie rivet diameter If joint

Edge Distance Rivet Spacing

d

Sotisfactory B e s t Head Hole B a c k Ciearonce Length

Sotis- Good Count- Capped Good Good Sotis- Satis-

foc tory ersunk f a c t o r y factory

Thick and Flush Joints Pivot Joints

a bracket or coniponcnt i n position

(3)-Rivet Spaciiig ‘Iliis also is a fimctioo of

application arid strength requirements

vary with rivet size Ilciglit and diameter Cali readily

he determined from specification sheets Vrcquently, the work can be countersunk, or tlie joint designed

to prevent interference with mating sections

pends on ivlietlier thc fastencr grips tllc wall or

c l i n c h iiiidcriieatli 111 tlic lattcr c x c , ovcr~izccl lioles are less critical, and one docs not clepcnd on wall cniistrictioii to prcveiit brcakout

(6)-Back Clearance Distance from flat of the liead to end of the uiiclinclied rivet determines the required back clearance-not dimensions after set- ting These values shouid take into account the maximum combined material thicknesses

(7)-Rivet Length There is a delicate balance behveeii joint thickness, mandrel-head dimensions, the cold-working propcrties of tlie rivet material and

( i f coiirse, the sliank dianicter of a blind rivet On the otlier hand, one length ran be nsed for a wide

For any use bcyond the tabulated data, actual limitations slionld be deter- mined b y test

General Design

(8)-Angles and Formed Sections ,\void obstruc- tions to the tool, which should sct flush on the work ’rhus, the “poor” joint reqiiircs a special off- set tool, iiiay still be inacccssible Reverse the rivet aiid set from the other side, or reduce the length

of the angular section

(9)-Cliannel Sections For adequate tool clear- ance, set from the underside of the clianncl or widen

the scction h tool extension niay he used to rrach

iiititle tlic section, I i i i t makes the tool soniewhat iiiorc awk\vard to Irairdle

(10)-Thick and ‘Ihin Sheets If there’s a choice, it’s best to set the rivet against the thicker inaterial Kivets of this type can be set against 0.030 in and tliinner aliuninum stock

obtained only by couiitersinking the outer wall or plate Dimpling generally is not recommended be-

C~JUSK of tlie possibility of the rivet not fully “bot-

toming” arid setting against the hole edge A

smooth, watertight, but not completely Rusli sur- face ic n1,taiiied hy cnrintersinking 2nd capping tlie riset