Surface gauge or scribing block

There are various types of surface gauges

(Figure 6.17), but in the main they consist of a very

accurately machined base, an adjustable pillar

Figure 6.16Wire gauges (metric) (Neill Tools Ltd

(Moore and Wright))

Figure 6.17Universal surface gauges (Neill Tools

Ltd (Eclipse))

194Repair of Vehicle Bodies

fastened to the base, and an adjustable clamp

attached to the pillar for holding the scriber. The

surface gauge is used in conjunction with a marking-

off table or surface plate to mark out very

accurate, parallel lines to a true surface. The

machined base enables it to slide over the surface

of the table while the scriber retains its accurately

set position. The scriber can be set at various

heights and angles in order to mark out different

jobs or parts of jobs with horizontal lines at a fixed

height above the surface of the marking-off table.

Scribed lines show up more readily on a work surface

that is first covered with a solution of copper

sulphate or marking compound.

Vee blocks

These blocks are made in matching pairs, and have

to be used in conjunction with a marking-off table.

They are made of cast iron with vees machined

accurately to 90° into the top of the block to hold

the work (Figure 6.18). Along each side of the

block runs a groove into which a clamp can be

fitted in order to secure round-shaped work in

place during marking off with scriber, try square or

scribing block. In order to make sure that you have

a matching pair of vee blocks, before using them

always check that each of the blocks is stamped

with the same number.

6.3.5 Engineer’s level

This is used for setting surfaces level and parallel

to a marking-off table. The base is machined

so that it can slide across the surface of the

work-piece, and if the surface is level then a bubble

in a tube across the top of the level lies at the

centre of its scale. The base of the level has a

concave groove along its length which allows it

to lie on curved work. Some levels are shown in

Figure 6.19.

Vernier caliper gauge

These calipers are made in a variety of types,

some being used for external measurements only

and others for both external and internal measurements.

Vernier calipers consist of a fixed

jaw attached to a main beam which is graduated,

and another jaw which slides along the main

beam. This sliding jaw is marked with the vernier

scale which coincides with the main scale when

the jaw is moved. The vernier scale is based on

the difference between measurement made on

two scales which normally have one division

difference. By careful use of this adjustment a

reading can be taken to 0.02 mm or 0.001 in

(Figure 6.20).

Figure 6.18Vee blocks (Neill Tools Ltd (Eclipse))

Measuring and marking-out instruments 195

Micrometer

The micrometer (Figures 6.21 and 6.22) is used to

measure and record accurately to 0.01 mm, or when

using a vernier micrometer to 0.001 mm. The size

of an object is measured by the contact principle,

which requires it to be positioned between the

anvil and the spindle head of the micrometer. The

micrometer has a C-shaped steel frame. An anvil

with a flat face is attached to one end of the frame

and the other end accommodates the spindle and

the barrel, which is graduated in linear measure.

The bore of the barrel is screw threaded and

engages the part of the spindle which is externally

cut to the same thread. The outer end of the spindle

has a ratchet stud and a thimble which is graduated

around its bevelled circumference. When this thimble

is turned it moves the spindle forward on to

the object to be measured, and in so doing moves

along the linear scale on the barrel. A locking ring

Figure 6.19Engineer’s levels (Neill Tools Ltd

(Moore and Wright))

Figure 6.20Vernier caliper gauge (Neill Tools Ltd

(Moore and Wright))

Figure 6.21Micrometer (Neill Tools Ltd (Moore and

Wright))

Figure 6.22External micrometers (Neill Tools Ltd

(Moore and Wright))

1 Spindle and anvil

faces

2 Spindle

3 Locknut

4 Sleeve

5 Main nut

6 Screw adjusting nut

7 Thimble adjusting

nut

8 Ratchet

9 Thimble

10 Steel frame

11 Anvil end

196Repair of Vehicle Bodies

is usually provided in the frame at the point where

the spindle emerges from the barrel, so that the

spindle can be locked in position after a measurement

has been taken. An object to be measured

is held squarely in position between the anvil and

the spindle, then the spindle is closed on the object

by turning the ratchet stud clockwise until it starts

to slip, indicating that there is a predetermined

pressure on the object. If there is no ratchet stud

the thimble is turned just until resistance is felt

to the turning; great care must be taken to avoid

over-tightening. Next the spindle is locked in position

by turning the locking ring and the reading is

taken. The working principle of the micrometer is

based on the distance a screw moves forward for

each turn made. The screw thread has a lead of

0.5 mm while the thimble and barrel are graduated

into divisions of 0.5 mm for the barrel and 0.01 mm

for the thimble. Therefore, one revolution of the

thimble moves it along the barrel for 0.5 mm. The

thimble has 50 equal divisions and as one revolution

of the thimble is 0.5 mm, then one of the thimble

divisions will equal:

There are a number of different types of micrometers

made to serve a variety of uses in the field of

precision engineering: internal micrometer, tube

micrometer, screw-thread micrometer, adjustable

micrometer, depth-gauge micrometer, tubular inside

micrometer, bench micrometer and gear-teeth

micrometer.

Questions

1 When would a body repairer need to make

templates?

2 Describe the making of a template and the types

of materials which could be used for this purpose.

10.5

_ 0.01mm

3 Make a list of measuring and marking-out

instruments which would be used in vehicle body

work.

4 Explain the type of steel that would be suitable to

manufacture a scriber.

5 Suggest an appropriate repair situation

which would require the use of a long straight

edge.

6 Explain the difference between a try square and

a centre square.

7 Explain the uses of a set of trammels.

8 Illustrate the two types of calipers which are used

in the workshop.

9 State the reasons why gauges are a necessary

piece of equipment in engineering.

10 Make a sketch, and state the operation of, a

micrometer.

11 Explain the term ‘datums’.Why are they used

when marking out?

12 With the aid of a sketch, illustrate the principal

parts of an engineer’s combination square.

13 Explain the use of the vee block when marking out.

14 What is the purpose of a marking-off table and a

surface gauge?

15 Explain the operation of a vernier caliper gauge.

16 State the effects of parallax error when

measuring with a steel rule.

17 Explain the purpose of a metre square when

marking out.

18 Describe a method by which a surface can be

checked to ensure that it is vertical.

19 With the aid of a sketch, show how to locate the

centre between two points using dividers.

20 Explain the difference between a radius gauge

and a drill gauge.

Methods of joining

7.1 Development of joining methods

In the manufacture of motor vehicles, the development

of new and more effective fastenings is

almost a branch of engineering in itself. However,

the traditional nut and bolt is still in use, and for

many applications it is difficult to imagine how it

can be replaced. Indeed, there are instances of a

return to nuts and bolts from newer methods of

fastening; some British and many continental cars

now have bolt-on wings or body panels where

previously welding was employed or the structure

was integral. The bolt has not changed much in

design since it was first developed, apart from the

use of special materials for certain applications and

also greater standardization of threads. Nuts, however,

are produced in a variety of special types; for

example, high-tensile steel bolts having greater

strength than hitherto use special shake-proof nuts

which form a very efficient fastening.

Solid rivets have also been used since the early

days of motor vehicle manufacture to form a permanent

joint, but nowadays riveted joints are being

replaced by welding.

In the field of mechanical fasteners, the modern

motor vehicle uses special types of spring-clip

fasteners in ever-increasing quantities. The most

usual form of such fastenings is the simple spring

clip made of tempered strip or wire; polythene,

nylon and other plastics fastenings have been used.

Another method is that of fastening panels together

using adhesives; this is proving to be very successful

in certain types of construction.

7.2 Solid rivets

The strength of a riveted joint depends on several

factors: the material in which the rivets and plates

to be riveted are made; whether the holes for the

rivets are punched or drilled; and the workmanship

involved in the riveting of the joint. In light sheet

metal, rivets are usually applied in the cold state so

that there is virtually no possibility of distortion.

However, in heavier metal plate riveted joints often

have to be comparable with the surrounding metal,

and so the rivets are inserted in the hot state as this

increases the strength of the joint.

Rivets used in hot riveting are made from steel

and/or iron, while for cold working rivets made

from copper, brass, aluminium and aluminium

alloys are used. In body work, steel rivets are used

on commercial chassis frames and also on fabricated

sections such as subframes and structural

load-bearing members. In addition aluminium

rivets are used on alloy frame construction in the

body building industry.

Rivets are classified according to the shape of

the head, and the diameter and the length of

the rivet. The shape of the rivet head is selected

according to the intended use of the workpiece to

be riveted. The diameter is selected according to the

required strength and thickness of the component

to be riveted. Most important, the length of the

rivet must correspond to the total thickness of the

components to be joined. The various types of

rivets are shown in Figure 7.1, together with their

British Standard proportions.

The snap or round head rivet is used where high

strength is required. The pan head, similar to the

snap head, is also used where strength is required.

The mushroom is used in thin sheet metal which

would be weakened by the use of countersunk

rivets. Flat head rivets are used for riveting flat bar

and angle sections to thin metal sheet as the head

is fairly flush and does not obstruct. The countersunk

head rivet is used when the surface of the

component must remain smooth.

Rivet holes

Rivet holes can be punched or drilled. Punched

holes are generally slightly conical, and for an

efficient joint the work has to be arranged so that

198Repair of Vehicle Bodies

the holes are brought together with their smaller

ends adjacent. Punched holes also have ragged

edges which must be smoothed, otherwise they

will decrease the shearing resistance of the rivets.

Drilling produces holes with smooth edges, and

has the further advantage that it can be carried

out with the plates in position so that there is no

damage due to badly aligned holes. A joint formed

with drilled holes is about 8 per cent stronger than

a joint made with punched holes. Table 7.1 gives

rivet and hole diameters.

Riveting dimensions

The diameter of a rivet is usually determined by

where D is the diameter of the rivet

and t is the thickness of the plate.

The allowance for riveting is the allowance

for the head of the rivet, and is the amount of

rivet showing above the plate before riveting. The

allowances are: snap head _ 1.5D; countersunk

head _ 0.15D; flat head _ 0.5D.

The pitch of a rivet is the spacing between the

rivet centres. It can be calculated from the principle

that the part of the plate between each pair of holes

should be the same strength as one rivet. Therefore

if the pitch is less than 3D (Figure 7.3) the plate

between the rivets will be too weak. The pitch can

then be extended to 8D in special cases, but above

that the plate will tend to buckle.

The width of lap is the distance from the centre

of the rivet to the edge of the plate. It is generally

taken as 1.5D, so that a single-riveted lap joint

would have an overlap of 3D (Figure 7.2) and a

double lap joint an overlap of 5D.

Types of riveted joint

The simplest form of riveted joint is the single lap

joint (Figure 7.2), in which the plates overlap a

short distance with a single row of rivets along the

D _ 1.2_t,

Figure 7.1Small rivet heads (BS 641)

Table 7.1Rivet sizes and hole diameters for solid rivets

Rivet diameter (mm) 2.38 3.17 3.96 4.76 6.35 7.93 9.52 12.70

(in) 0.094 0.125 0.156 0.187 0.25 0.312 0.375 0.5

Hole diameter (mm) 2.43 3.25 4.03 4.85 6.52 8.02 9.80 13.10

(in) 0.096 0.128 0.159 0.191 0.257 0.316 0.386 0.516

Methods of joining 199

centre of the lap. The double-riveted lap joint has

two rows of rivets arranged either in line or staggered

alternately. The single-strap butt joint consists

of two plates butted edge to edge with a strap

covering the centre of the butt and riveted down

each side (Figure 7.3). The double-strap butt joint

is the same as the single-strap butt joint with the

addition of a second strap on the opposite side.

A single-riveted joint has an efficiency of only

about 55 per cent. In a double-riveted joint this

is raised to about 70 per cent, whilst in a trebleriveted

joint 80 per cent or greater efficiency may

be attained.

Riveting procedure

Plates to be riveted should be clamped together

with their rivet holes in alignment. If hot rivets are

being used, they should be at forging temperature

and the operation should be completed before they

become ‘black’ hot. For snap head rivets, a punch

or tool (snap) having a half-spherical cavity similar

to the rivet head is used to support the rivet head,

while the other-end of the rivet is riveted over by

holding a similar punch to the rivet end and striking

it with a hammer, thus forming a second cup head

on the other end of the rivet. The aim in riveting is

to swell the body of the rivet until it completely

fills the holes, and to complete the process as

quickly as possible while the rivet is still very hot

so that there is maximum contraction of the rivets

after riveting to pull the plates together. Pneumatic

or air operated hammers are used extensively for

closing over rivet heads. They are designed to

deliver the right weight of blow at the correct speed

to form the rivet head speedily and accurately. For

cold riveting the closure of the rivet is similar to

that of a hot rivet except that the metal is not as

plastic and greater difficulty will be encountered in

swelling the rivet shank to fill the hole. Cold riveting

plates cannot be as tight as with hot riveted

because there is no contraction of the rivets to pull

them together.

Care should be taken that the rivet head is spread

evenly in all directions and not bent over in one

direction only. This is often helped by giving the

rivet a few preliminary blows with the ball end of

the hammer, thus spreading the rivet a little before

using the riveting tool (Figure 7.4). Countersunk

rivets should be supported with a flat-headed

punch. The initial spreading is done with the ball

end of the hammer and the head is finished with

the flat end of the hammer. When riveted joints are

large it is advisable not to start at one end of the

workpiece but to rivet the extremities first and next

the centre, then the rest of the joint. This eliminates

creeping of the plates and misalignment of the

holes.

7.3 Bifurcated, tubular and semitubular

rivets

These rivets have the outstanding advantage that

there is no swelling of the solid portion of the

shank during the closure operation. They are used

extensively for the joining of soft materials such

as plastic, rubber, leather and/or brake and clutch

linings to metal. Only a small percentage is used

in the body building industry.

Figure 7.2Single-riveted lap joint

Figure 7.3Butt joint

200Repair of Vehicle Bodies

7.4 Blind rivets

The blind rivet was originally developed in the

1930s for use in the aircraft industry, but since then

it has been adopted in the light engineering industries.

It is now employed as a standard sheet metal

fastener in cars, buses and all forms of commercial

vehicles. Blind rivets, as their name implies are

rivets which can be set when access is limited to

only one side of a structure. They are invaluable

both in car construction work, where many of the

panel assemblies are of the double-skinned type

so that accessibility would be impossible for conventional

riveting methods, and also in body repair

work as they eliminate any unnecessary stripping of

interiors. Blind rivets are manufactured by several

companies under brand-names, the most famous of

which is POP. POP is the registered trademark of

Tucker Fasteners Limited who were the pioneers

of blind riveting.

Blind rivet types

POP rivets

The POP rivet comprises a hollow rivet assembled

to a headed steel mandrel or stem (Figure 7.5). It is

inserted into a predrilled hole of the correct size in

the workpiece, and a special tool containing a

gripping device is applied to the mandrel or stem

of the rivet. When the tool is operated, either manually

or automatically, the mandrel head is drawn

into the hollow rivet, expanding the end of the rivet

which is on the blind side of the structure and at

the same time pulling the material together. When

and only when, a tight joint has been formed, the

mandrel breaks at a predetermined position, so that

the mandrel head is left as a plug in the bore of the

rivet (Figure 7.6). The spent portion of the mandrel

is then ejected from the tool. POP rivets are manufactured

from aluminium alloys, Monel, mild steel,

copper and stainless steel. They are supplied with

domed or countersunk (90°, 100° or 120°) heads in

diameters of 2.4 mm, 3.2 mm, 4.0 mm, 4.8 mm and

6.4 mm, for riveting thicknesses up to 12.7 mm.

Shear strengths range from 400 N for 2.4 mm diameter

aluminium alloy rivets, to 5400 N for 6.4 mm

diameter Monel rivets. Owing to the high clenching

action of the rivet, tensile strengths are in excess of

these figures.

Seven types of POP blind rivet are shown in

Figure 7.7. These and other types are described as

follows:

Standard open rivet is subdivided into the breakhead

mandrel type, which leaves the mandrel head

Figure 7.4Riveting procedure

Methods of joining 201

free to fall away from the rivet (Figure 7.6), and the

break-stem mandrel type, which retains the broken

portion of the mandrel within the set rivet, thus

sealing the rivet to a certain extent. The latter type

is intended for use in all normal blind riveting

situations where the materials to be fastened do not

present structural problems. This is a hollow rivet,

preassembled on to a headed pin or mandrel.

The mandrel is designed to fracture at a predetermined

point during the setting operation, when the

materials to be fastened have been drawn closely

together and the joint is tight. Sealed rivet consists

of a tubular rivet with a sealed end containing

a steel or stainless steel mandrel. The riveting

sequence is similar to that of a POP rivet, but this

type has the advantage that in setting the rivet it

is both compressed beyond its elastic limit and

expands radially, thus ensuring a joint which is

airtight and watertight up to 34 bar. The rivet is

available with two alternative mandrels: one, called

‘short break’ (Figures 7.8 and 7.9), fractures immediately

under the mandrel head which is retained

in the blind end of the set rivet; and the second,

known as the ‘long break’ type, fractures at a point

outside the rivet and can be finished off to result in

a flush finish. The sealed rivet is a fastener of high

shear and tensile strength and vibration resistance.

Owing to its high rate of expansion in setting, it cannot

be recommended for use in very soft or brittle

materials. It is designed for use where the fastening

to be used has to be pressure or water tight.

LSR rivet This range of aluminium rivets is

designed to offer two particular advantages in joining

soft friable or brittle materials. Its controlled

setting gives outstanding reliability and it produces

a neat uniform appearance. The LSR is suited to

plastics, wood, GRP laminates and thin gauge materials.

It has an important role to play in such applications

as the assembly of caravans and trailers.

MGR rivet has been designed for use in situations

where hole sizes are inconsistent. It also

offers a multi-grip facility. The rivet is available in

aluminium 2.5 per cent magnesium alloy with a

carbon steel mandrel. MGR is valuable where

components are supplied to the user with holes

already punched or drilled, or where the sheets to

Figure 7.5POP blind rivet: standard open type

(Tucker Fasteners Ltd)

Figure 7.6POP blind rivet, standard open type:

setting sequence (Tucker Fasteners Ltd )

202Repair of Vehicle Bodies

be joined are folded or curved, making it difficult

to match up two holes of the correct size.

Grooved rivet has been developed for use in thick

sections of soft or brittle materials such as hard

board, plywood, glass fibre, asbestos board, concrete

and brick. The POP grooved rivets gain their

name from the series of grooves around the shank

which engage into the workpiece on setting and set

inside the material rather than against the rear face.

Construction and setting action is similar to the

standard open type. The body is of aluminium alloy

with a carbon steel mandrel. When set, this rivet

is capable of withstanding high pullout loads (see

Figures 7.10 and 7.11).

Figure 7.7Types of POP blind rivet (Tucker Fasteners Ltd )

Figure 7.9POP blind rivet, sealed type: setting

sequence (Tucker Fasteners Ltd )

Figure 7.8POP blind rivet: sealed type (Tucker

Fasteners Ltd )

Methods of joining 203

Peel rivets are specifically developed for fastening

soft or friable materials. They will secure blowmoulded

or glass-reinforced plastic, rubber and plywood

to metal panels or sections up to 13.5 mm

thick. The rivet has an aluminium alloy body and a

special carbon steel mandrel. On setting, the rivet

body is split into four petals by the action of the

mandrel head, producing a large blind-side bearing

area capable of withstanding high pullout load (see

Figures 7.12 and 7.13).

ELF rivet is an aluminium 3.5 per cent magnesium

alloy with an aluminium alloy mandrel. The body

of this rivet splits and folds on setting to form three

neat leaves which spread clamp-up load over a wide

area. It is a totally sealed rivet designed for use on

roofing but is suitable for materials like composite

board, GRP, hard rubber and laminates, and is used

in commercial vehicle construction and caravans.

Special POP rivets are shown in Figure 7.14. Earth

terminal rivets are designed to provide an effective

Figure 7.10POP blind rivet: grooved type (Tucker

Fasteners Ltd )

Figure 7.11POP blind rivet, grooved type: setting

sequence (Tucker Fasteners Ltd )

Figure 7.12POP blind rivet, peel type: before setting

(Tucker Fasteners Ltd )

204Repair of Vehicle Bodies

earth connection to pre-painted sheets without

damaging the finish. Tab rivets are designed to perform

two or more functions, such as fastening the

tops of rechargeable batteries and at the same time

providing a tab to serve as a connector. Tamperproof

rivets are set in the workpiece with a standard

tool; a stainless steel pin is then tapped into the

bore of the rivet and its domed head locates in a

recess in the rivet head, making the fastening virtually

impossible to remove without obvious traces.

T-rivets are designed for exceptional strength and

versatility; they can be reliable and vibration-proof

in holes as much as 0.8 mm oversize.

Blind rivet nut is a threaded insert system, and is

a remarkably simple fastening system for use in all

kinds of assemblies. It provides a straight, reliable

threaded insert to which other components can be

attached. It can be used as a blind rivet for permanently

fastening one or more panels or sections

together, and provides an anchorage with the holding

strength of at least six full thread turns. It can

be installed at any stage without damaging the

work-piece finish, even after painting. It can be

used in materials with thicknesses varying between

0.25 and 7.5 mm. There are a wide range of sizes

available in steel, aluminium or brass with thread

sizes from M4 to M10. (M is the metric screw

thread designation, and when followed by a number,

e.g. M4 is a metric thread of 4 mm diameter.)

Sealed or open types are available with flat or

countersunk heads. They can be used in drilled or

punched holes with normal tolerances (Figure 7.15).

Well nut This demountable blind screw anchor

is designed to provide a vibration-resistant fixing

for engineering and automotive structures. It consists

of a captive brass nut in a resilient neoprene

bush which can be installed from one side of the

workpiece using only a screw and a screwdriver

(Figure 7.16). It is suitable for materials from light

gauge metal panel, too thin for self-tapping or

set screws, to plastic sheet up to 16.5 mm thick.

The flanged ends prevent electrolytic corrosion at

metal-to-metal assembly points.

Repetition rivets

Repetition riveting systems are widely used on

vehicle body construction, especially commercial

vehicles. Some examples are as follows:

Chobert riveting system operates on an entirely

different principle from other blind riveting systems

(Figure 7.17). Instead of a break-stem type of mandrel,

there is a mandrel with a tapered hardened

Figure 7.13POP blind rivet, peel type: after setting

(Tucker Fasteners Ltd )

Figure 7.14Special POP rivets (Tucker Fasteners Ltd )

Methods of joining 205

steel head larger in diameter than the tapered bore

of the rivet. The mandrel is drawn through the rivet

towards the head, and is thus part of the placing

tool rather than the component. It is possible

to extend the mandrel length to accommodate a

charge of up to 100 rivets and to achieve a rate of

placing up to 2000 per hour. The Chobert rivet is

made in a wide range of materials and sizes. Head

forms currently available include snap, mushroom,

flat and countersunk, and sizes range from 2.38 mm

to 6.35 mm diameter. Materials include a wide

range of aluminium alloys and zinc-plated steel.

They are supplied in tube loaded form, each

317.5 mm long and containing up to 100 carefully

aligned rivets. The tubes can be used in special

tools which can be either manually or pneumatically

operated. If additional strength or water

tightness is required the rivets can be pinned,

giving in effect a solid rivet.

Chobert Grovit system has been developed so that

the widest range of materials (such as wood, plastic,

aluminium) may be joined. The Grovit has grooves

on its shank which bite firmly into the material when

Figure 7.15Blind rivet nut, installation sequence

1 POP nut screwed on to tool

2 POP nut inserted into hole

3 Tool operated: mandrel retracts into tool, and

unearthed part of nut expands on blind side of

workpiece

4 Tool mandrel unscrewed

5 Assembly completed

Figure 7.16Well nut (Tucker Fasteners Ltd )

Figure 7.17The Chobert hollow rivet (Avdel Ltd )

206Repair of Vehicle Bodies

the rivet is expanded (Figure 7.18). The rivets can

also be used in the high-speed Chobert system. These

types of riveting systems are ideal for mass production

and are invaluable in the body building industry

where speed and economy are essential (Figure 7.19).

Briv system is a high-speed, high-clench riveting

system for use with a wide range of assembly materials.

Briv is installed from one side of the workpiece

with the use of a mandrel loaded into the Avdel

power tool. The action of the mandrel draws through

the rivet, expanding the shank to fill the hole. The

applications range from body component assembly

to fixing electronic control panels (see Figure 7.20).

Blind riveting tools

The majority of blind riveting tools have been

designed on the assumption that the operator will

be moving around a stationary structure, as in body

building. However, some stand tools are available.

Figure 7.18The Chobert grooved rivet (Avdel Ltd )

Figure 7.19The Chobert and Grovit riveting systems (Avdel Ltd )

1 2 3 4

Figure 7.20Briv placing sequence (Avdel Ltd )

1 Place Chobert rivet or Grovit in prepared hole

2 Draw steel mandrel, which has opposite taper to rivet, through from tail end of rivet, expanding rivet tail

around rear side of hole, to form shoulder. (For the Grovit, annual convolutions are forced into materials.)

3 Continue to pull the mandrel through rivet, which symmetrically expands shank to fill hole

4 The rivet has good bearing in hole and a parallel bore is left in the rivet

1 Magazine loaded rivet is

placed into hole

2 Tool draws mandrel through

rivet, compressing rivet

3 Mandrel expands shank of

rivet to fill hole and clamp

materials

4 Completed rivet. Tool

reloads automatically

Methods of joining 207

The range of tools has been designed to cater for

all riveting conditions, whether they are used on

high-speed assembly production lines or for occasional

use. The basic types of tools consist of:

1 Manually operated plier types

2 Manually operated lazy tongs

3 Portable pneumatically operated guns

4 Portable pneumatic hydraulic guns

5 Pneumatically operated stand tools.

In addition various heads are available for attaching

to either manual or power operated tools which can

gain access to restricted places. In order to change

the rivet diameter or type of rivet being used, it is

necessary merely to change the nose-piece or the

gripping jaws which hold the mandrels. It must be

remembered that certain special rivets and fasteners

can only be used by their appropriate setting tool.

Some examples of riveting tools are given in

Figures 7.21–7.24.

Hole size Drill sizes for each diameter of rivet are

usually specified by the manufacturers. These are

usually designed to give a clearance of 0.05 mm to

0.13 mm between the rivet and the hole, and in the

case of rivets capable of only limited radial expansion

these recommendations must be followed if

maximum efficiency is to be achieved.

Rivet length Manufacturers also specify the correct

rivet length to be used on a given thickness

of material. It is often advantageous to use rivets

which are longer than those recommended as they

will set satisfactorily on thinner materials, and the

longer length, when expanded, increases the grip

of the rivet, but the higher cost for longer rivets

should be taken into account before doing so.

Pitch of rivets In load-bearing joints the distance

between rivets in the same row should not exceed

six times the rivet diameter. Even when the joint is

not load bearing, the rivet pitch should not exceed

Figure 7.21Hand operated riveting tool, plier

type (Tucker Fasteners Ltd )

Figure 7.22Hand operated riveting tool, lever type

(Tucker Fasteners Ltd )

Figure 7.23Hand operated riveting tool, lazy tongs

type (Tucker Fasteners Ltd )

Rivet selection

The following factors must be considered when

selecting the type of rivet to be used on a particular

job:

Rivet diameter In some cases this may be decided

by the size of an existing hole. When designing

new work the main factor is usually the shear or

tensile strength required from the riveted joint. In

load-bearing joints the diameter of the rivet should

be at least equal to the thickness of the thickest

sheet but should not be greater than three times the

thickness of the sheet.

208Repair of Vehicle Bodies

twenty-four times the thickness of the thinnest

sheet in the joint.

Edge distance In lap or butt joints which are

likely to be subjected to shear or tensile loads rivet

holes should not be drilled within a distance equal

to two rivet diameters from the edge of the sheet,

but should not exceed twenty-four rivet diameters.

Rivet material The choice of rivet material will

normally be related to the strength required from

the riveted joint. Usual rivet materials are steel,

aluminium alloy, copper and Monel. Other factors

affecting the choice are weight, high temperatures

and corrosion resistance, especially electrolytic

corrosion which can occur when different metals

are joined together.

Mandrel type The break-stem mandrel is usually

chosen where the rivet is to act as a waterproof

plug, and also where it would be inconvenient to

eject the mandrel head on the blind side of the

enclosed structure. The break-head mandrel is used

where weight is a factor, and where a comparatively

clear hole is required through the rivet set.

7.5 Structural fasteners

Figure 7.25 shows a variety of structural fasteners

used on a vehicle body.

Figure 7.24Automatic riveting system (Tucker

Fasteners Ltd )

Figure 7.25Types of structural fastener used on a vehicle body (Avdel Ltd )

Methods of joining 209

Avdelok system

This is not a blind fastener, but has a number of

advantages over the conventional rivet or nut and

bolt which it replaces. The Avdelok is a two-piece

high-strength fastener consisting of a bolt and

collar made from carbon steel, stainless steel and

aluminium alloy (Figure 7.26). It gives a high clench

action and a positively locked nut or collar which is

proof against vibrations. It can be placed very simply

by manual or pneumatic tools. The Avdelok bolt is

placed through the prepared hole and the collar is

slipped on to the other side of the joint (Figure 7.27).

The nose of the tool is then pushed over the tail of

the bolt and the trigger is pulled. This draws the

bolt tight, clamping the sheets together. The pull

continues until the nose of the tool is drawn over the

collar, compressing the collar until it is swaged into

the grooves of the pin. The tail of the bolt breaks off

at the deep breaker groove, flush with the collar. No

finishing is needed. This system is employed in such

applications as chassis cross-bearer brackets on commercial

vehicle bodies.

plated and gold passivated to ensure good corrosion

resistance. The fastener is supplied in 6.4 mm

diameter in various lengths. It is installed from one

side of the workpiece, thus making it a blind fastener.

It is designed with a chamfer at both ends

of the stem; this facilitates easy insertion into the

placing tip of the installation equipment, and into

the hole in the workpiece. The installed fastener

breaks flush with or below the surface of the lowprofile

Hemlok head, leaving a clean finish and

appearance. Hemlok provides strength and good

clamp-up, and the well formed fastener tail

achieves this without deforming thin sheet material.

This fastener is designed to be used on thin-gauge

materials for high-strength joints suited to automotive

work (see Figures 7.28 and 7.29).

Threaded inserts

Steel threaded inserts (such as Nutsert) of high

strength (Figure 7.30) can be placed by any of three

specially designed tools. The Nutsert is placed on

the threaded drive screw of the placing tool and

inserted into a prepared hole in the workpiece.

The drive screw turns clockwise drawing the

tapered nose portion of the Nutsert back into its

outer shell and thus causing the shell to expand into

the preformed hole. The drive screw is then withdrawn,

leaving the Nutsert permanently and tightly

placed in the hole and ready to receive either a

screw or a bolt. It can be used on all types of metals

and also plastic and timber, and is made in a wide

range of thread sizes, both imperial and metric

(Figure 7.31).

Figure 7.26The Avdelok fastener (Avdel Ltd )

1 Insert Avdelok pin through predrilled hole and slip

collar over pin tail

2 Place tool nose over pin tail and press trigger

Figure 7.27The Avdelok system (Avdel Ltd )

3 Swage collar into locking grooves of pin

4 Tail of pin breaks flush with collar and is

ejected

Hemlok system

The Hemlok is a blind fastener which comprises

a steel stem and shell. Both components are zinc

210Repair of Vehicle Bodies

Monobolt system

Monobolt is a precision engineered two-part component.

It is a high-performance flush-break fastener

designed to build in strength, security and

quality. It consists of a body and a stem and is

supplied as a one-piece assembly. A sealing on

the Monobolt stem provides exceptional resistance

to moisture, an essential requirement for many

applications in vehicle body work. The fasteners

are available in aluminium alloy, carbon steel

and stainless steel, in diameters of 4.8 mm and

6.35 mm. Fast and simple to install, Monobolt is a

Figure 7.28Hemlok fastener (Avdel Ltd )

Figure 7.29Hemlok placing sequence (Avdel Ltd )

1 Hemlok inserted into power tool and workpiece

2 Tool operated: Hemlok tail deforms over material

Figure 7.30Standard Nutsert (Avdel Ltd )

3 Tail fully formed: fastener stem breaks off

blind fastener, ideal for original structural assembly

and to replace conventional fastening methods,

particularly when access to the workpiece is difficult.

A major feature of the Monobolt construction

is the visible locking element which allows

easy, visible inspection after placement (see

Figure 7.32).

Avtainer system

This system has been designed for the joining

of composite panels of plywood and glassreinforced

plastic to metal framing. This fastener

has the ability to join firmly, but without cracking

or pulling the bolt right through the composite. It

is a two-piece fastener consisting of a zinc-plated

carbon steel pin with a nylon seal and a collar

which is pulled tight from the other side of the

workpiece, thus causing no damage to the material

during installation. One of its main applications

is in the building of commercial vehicles

(see Figure 7.33).

Methods of joining 211

7.6 Screws and bolts

Wood screws

Joining by wood screws is an essential part of the

construction of vehicle bodies which incorporate

timber. Screws are available in steel, brass and

bronze, with a variety of alternative finishes. Sizes

range from no. 2 (1.6 mm in) to no. 8 (7.9 mm,

in), and lengths vary from 6.35 mm, in, up to

101.6 mm, 4 in and longer in special cases. The

head types include the standard countersunk (used

in most timber fixings), round head (sometimes

used when fixing metal fittings to wood), and raised

head (used when fixing mouldings where the raised

head gives a decorative effect) (Figure 7.34). A new

development is the Supadriv recess head, specially

engineered to give a ‘cling-fit’ between driver and

screw; it is increasingly used in robotic assemblies.

In body shops wood screws are applied by hand or

with special power operated screwdrivers which are

either electrically or pneumatically operated.


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