Crankpin bearing (4CR 603)

Plastic stub axle

Axle sleeve

Moulded wheel centre

Wheel rim

M1 screw (4CR 601)

Aluminium insert (4CR 602)

Axle cap (4DW 103)

Centre boss with

bearing surface

Frame

Operating screw

Removable sleeve ‘B’

Removable anvil ‘A’

Score here

Mould feed

Round

section

Taper

section

Stub axle

Location of mould pip (if any)

Removable anvil ‘A’

Removable sleeve ‘B’

Drop of Loctite here

Axle sleeve

Axle sleeve centred

between wheel bosses

Exactoscale Back to

Back gauge

M1 countersunk screw

Threaded crankpin bearing

Aluminium insert

Moulded wheel centre

Instructions for Assembling Driving Wheels, Axles and Crankpins

(Version 1; October 2008)

Introduction

These instructions explain how to assemble Exactoscale 4mm scale driving wheels, axles and crankpins to produce a

wheelset that is has the desired back to back setting, has wheels that run true and crankpins with a consistent throw.

The design features that help to achieve this result will only work properly if the correct assembly procedure is

followed. It is therefore important to read these instructions carefully and understand the reasons for the sequence

that is described.

Successful assembly of the wheels and axles (and subsequent removal of wheels from their axle) depends on the use

of a small press specifically designed for the purpose. Attempting to assemble or dismantle wheelsets without using

the press is likely to result in damage.

The drawings in these instructions show a 6’ 8” driving wheel but the methods used (and the press tool) will be

applicable for any future wheels introduced that use this design of axle.

Concept

The design features a taper joint between the wheel and axle. Tapers of a shallow enough angle, when pressed firmly

together, form a secure ‘locked’ joint which provides the kind of accurate location needed for a true-running wheelset.

No adhesive is needed in the taper joint and this means that the taper can be released and the wheels removed by

pressing the axle out of the centre of the wheel...... and then reassembled by pressing the wheel back on to the

tapered axle.

The difficulty with shallow-angle tapers is that the position at which they lock is very sensitive to small changes in the

dimensions of either of the components involved - a manufacturing nightmare if the aim is to make an axle with a

taper on both ends which will ensure both wheels are locked at the required back to back dimension.

Our solution is a three-part axle which is assembled by the modeller - this forming the first part of the assembly

sequence. We strongly advise that, when wheelsets are dismantled, care is taken to keep each axle with the wheels it

was initially assembled with.

This shows the cross-section of an assembled wheelset - the three-part axle and taper joints can be seen together

with the wheels with their bearing surfaces integral with the wheel. The grooves in the bearing surfaces are to assist

oil retention.

The press tool shown in cross-section below consists of a frame and screw with two small components - one to fit in

the frame (’A’) and one to fit on the screw (’B’). These enable the tool to be used in several different ways.

Assembling an Axle

An axle consists of a central metal sleeve with two plastic stub axles. This section describes how to assemble these to

produce an axle of the required length so that the taper joints will lock at the required back to back dimension.

First, prepare the stub axles. These are made of a special hard plastic (Torlon) and need care when they are being

detached from their sprue to avoid lifting the surface skin. Score the mould feed with a scalpel where shown in the

cross-section view below and break the stub axle from its sprue by bending in the direction shown. Use a scalpel to

clean off any remaining roughness that protrudes above the round surface of the stub axle.

Before going further, examine the wheels carefully to make sure that there is no mould sprue material sticking out

beyond the back face of the wheel rim. The mould is filled at a point on the back face of the wheel in line with the

crankpin boss, and it is here that you may find a small raised mould pip (see below). Trim it flush with the back of the

wheel with a scalpel.

Now put the other end of the stub axle in the removable anvil (component ‘A’) of the press tool and put component ‘A’

with the stub axle and wheel in position in the press tool frame as shown in the smaller picture below. Put the remov-

able sleeve ‘B’ in position on the end of the operating screw and screw the screw in until the end of ‘B’ engages in the

centre of the wheel, pressing on the metal centre boss, as shown below. Tighten the screw, making sure the end of ‘B’

is pressing on the metal boss and not the plastic moulding, and then tighten the screw very firmly - but using just

fingers on the screw knob - do not use other tools to get it even tighter.

Repeat all this for the other wheel and stub axle so that you have two wheels firmly locked on their stub axles.

Now to assemble the axle - and please note the following:

i) A dry run axle assembly is worth doing - the work needs to be completed reasonably quickly, before the Loctite sets;

ii) When using Loctite, avoid contact with the liquid and observe the safety instructions provided;

iii) Do not pay any attention at this stage to wheel quartering - that comes later.

Apply a small drop of Loctite 603 (or 638) to the surface near the inner end of one stub axle and spread it round the

circumference. Park the wheel while you put Loctite in one end of the axle sleeve (a more generous drop is OK here).

Now push the stub axle into the sleeve, twisting the sleeve to spread the Loctite evenly. Apply Loctite in the same way

to the other stub axle and into the other end of the sleeve and push the second stub axle into the sleeve, again

twisting the sleeve. Wipe surplus Loctite off with a tissue and place the wheelset in the back to back gauge.

With finger and thumb, hold the wheels against the gauge, pressing gently along the line of the axle. Using a small

screwdriver, adjust the position of the sleeve so that the gaps at each end between it and the inner ends of the wheel

bearing surfaces are the same on both sides. Continue holding the wheels in place for a few minutes and then leave

them standing for an hour or so - by which time the Loctite should have gone off sufficiently for the wheelset to be

removed from the gauge. Best to leave the wheelset overnight, though, before doing any more work on it.

You now have a wheelset that can be dismantled and reassembled, each time with the tapers locking at the correct

back to back dimension and with the wheels running true.

Working on the Wheelset

A range of further steps will be necessary before the wheelset will be installed in a working locomotive - including, for

example, fitting bearings, adjusting sideplay with washers, fitting crankpins, quartering (or whatever angle is appropri-

ate between the crankpins on opposite sides of your loco), fitting return cranks, fitting balance weights and so on.

Many of these require dismantling of the wheelset and for others, while dismantling may not be essential, it can make

the job easier. This section therefore covers dismantling and reassembling the wheelset.

First, a comment on loco design. To use the press tool to dismantle a wheelset, it is necessary for the wheelset first to

be removed from the loco chassis. Some kits and approaches to chassis design do not allow for this and it is suggested

that modifications are made so that removal is possible. Trying to dismantle a wheelset while it is still installed in a

chassis is likely to result in damage to the wheelset, chassis, or both.

To dismantle a wheelset, remove components ‘A’ and ‘B’ from the press tool and place the wheelset in the press tool as

shown on the left below.

Screw the operating screw in, making sure the narrow tip of the screw bears on the end of the plastic stub axle and

does not catch on the metal boss of the wheel - see the right-hand picture above. Tighten the screw until, quite

suddenly, the taper is released and the axle drops

out of the wheel boss. This should not need anything

more than firm finger pressure on the screw knob of

the operating screw. The procedure can be repeated

for the other wheel, though for most work on the

wheels, removing one wheel is likely to be sufficient.

A dismantled wheelset is shown on the right, with

the three-part axle in its final, assembled, form.

These instructions will not (for now, at least) cover most of the other work that might be done on the wheels - though

notes on crankpin assembly and quartering are included later. But once any work has been completed, the wheelset

will need to be reassembled, as follows.

Push each wheel boss onto its end of the axle, then gently squeeze the wheelset between thumb and forefinger (at

this point, the tapers will be binding sufficiently for the quartering to be tested - see next section). Place components

‘A’ and ‘B’ in position in the press tool, though this time with component ‘A’ reversed, with the solid end (which fits

inside the wheel moulding and engages with metal wheel boss) facing the operating screw.

When the wheelset has been assembled for the final time, axle caps (4DW 103) can be glued into the wheel centres to

give the proper axle end appearance. We suggest an adhesive that does not set too hard (possibly even Blutack) is

used to minimise the risk of damage if removal is eventually necessary.

Quartering

No special provision has been made for quartering and it is therefore necessary to do it by eye or make or obtain some

appropriate fixture. Remember, though, that it is not necessary to achieve an exact angle - just to get the same angle

on all the wheelsets.

The ability of the locking tapers between the wheels and axles to be ‘lightly locked’ with finger pressure, tested for free

running and then adjusted if necessary by simple twisting of the wheels may help. Final setting to the correct back to

back dimension (as above) would then only be done when satisfactory quartering has been achieved.

Take a wheel and stub axle, check that the taper of the

stub axle and the bore of the wheel are clean, and push

the taper section of the stub axle into the wheel so that

it is finger-tight - to give the result shown on the left.

Even at this stage, you should be able to feel some

locking effect between the stub axle and the wheel.

Place the wheelset in the press tool,

fitting the front face of one wheel

on component ‘A’ and screwing the

screw in until component ‘B’ sits in

the recess in the front face of the

other wheel, as shown on the left.

Do not tighten the scew further yet.

Now place a back to back gauge between the

wheels, as shown on the right. The back to back

gauge will rest conveniently on the press tool.

Tighten the screw so that the wheels are pressed

more tightly onto the tapered ends of the axle.

As you do this repeatedly check how easily the

back to back gauge moves up and down between

the wheels. At some point, the play between the

wheels and the gauge will be eliminated and the

wheels will just begin to bind on the gauge - this

is when the wheels are correctly gauged. Undo

the operating screw and remove the gauge and

wheelset. Check that the gauge still can slide

betwen the wheels without any play and then roll

the wheelset on a flat surface to confirm that the

wheels run true.

Crankpins

The Exactoscale crankpin range is based on M1 countersunk stainless steel screws, located in an aluminium insert that

fit in a recess moulded in the back of the driving wheel. A shouldered (’top hat’) threaded phosphor bronze bearing is

screwed onto the M1 screw, clamping the moulded wheel centre between the aluminium insert and the ‘top hat’

bearing. The cross-section drawing below shows these components.

To assemble a crankpin, first check the recess in the back of the wheel. It is important that there is nothing preventing

the aluminimum insert fitting correctly in the recess as otherwise it (and the screw head) will not be flush with the

back face of the wheel. It is also important not to deepen the recess as that could prevent the insert and the crankpin

bearing clamping the wheel moulding properly. Then push an aluminium insert into the recess, checking that it is flush

with the back of the wheel (see first drawing below). Take an M1 countersunk screw and check that there are no burrs

at the end of the slot in its head that could prevent it sitting correctly in the countersink. Use a needle file to remove

them if there are any. Push the M1 screw into the aluminium insert (see second drawing below).

Take a threaded crankpin bearing (reduce its length if it is too long for the thickness of the coupling rods being used)

and, holding the bearing surface in a pin chuck, screw it onto the M1 screw. If you are confident that the crankpin will

not need to be removed (or have its position adjusted to get a return crank correctly angled), put a drop of Thread-

locker (Loctite 243) on the screw before finally tightening it to clamp onto the moulded wheel centre. The third

drawing below shows the crankpin in position.

The Exactoscale range of crankpin components includes a threaded bearing extension, spacer washers and two sorts of

crankpin nut (round and hexagonal).

It may be possible to use the round crankpin nut reversed for the recessed nut that is sometimes needed on the

leading coupled wheels of an outside cylinder loco, though considerable thinning of the ‘top hat’ crankpin bearing will

probably be needed to give an acceptable overall crankpin length.

It may also be possible to use the threaded bearing extension to create a robust return crank. Thread a bearing

extension onto an M1 screw (right up to the head). Drill a 1.0mmØ hole in a thick piece of aluminium (or MDF might

do) and place the M1 screw in it - so keeping the bearing extension square to the surface of the aluminium/MDF. Open

out the return crank to 1.5mmØ and place it front face downwards over the bearing extension, then run a bead of

solder round the join between the return crank and bearing extension. Unscrew the M1 screw and screw the return

crank assembly tightly onto the crankpin, check its position and work out the amount of any angular adjustment

needed. Remove the return crank from the crankpin, loosen and retighten the cranpin having made the necessary

adjustment in the position of the screw slot and replace and retighten the return crank. It may take several attempts

but it should be possible using this method to get the return crank tight in the correct position.

As will be obvious, this section does not yet reflect much actual experience of using these components. It will be

extended and updated in due course. Feedback from modellers to help with this will be welcomed.

Crankpin bearing (4CR 603)

Plastic stub axle

Axle sleeve

Moulded wheel centre

Wheel rim

M1 screw (4CR 601)

Aluminium insert (4CR 602)

Axle cap (4DW 103)

Centre boss with

bearing surface

Frame

Operating screw

Removable sleeve ‘B’

Removable anvil ‘A’

Score here

Mould feed

Round

section

Taper

section

Stub axle

Location of mould pip (if any)

Removable anvil ‘A’

Removable sleeve ‘B’

Drop of Loctite here

Axle sleeve

Axle sleeve centred

between wheel bosses

Exactoscale Back to

Back gauge

M1 countersunk screw

Threaded crankpin bearing

Aluminium insert

Moulded wheel centre

Instructions for Assembling Driving Wheels, Axles and Crankpins

(Version 1; October 2008)

Introduction

These instructions explain how to assemble Exactoscale 4mm scale driving wheels, axles and crankpins to produce a

wheelset that is has the desired back to back setting, has wheels that run true and crankpins with a consistent throw.

The design features that help to achieve this result will only work properly if the correct assembly procedure is

followed. It is therefore important to read these instructions carefully and understand the reasons for the sequence

that is described.

Successful assembly of the wheels and axles (and subsequent removal of wheels from their axle) depends on the use

of a small press specifically designed for the purpose. Attempting to assemble or dismantle wheelsets without using

the press is likely to result in damage.

The drawings in these instructions show a 6’ 8” driving wheel but the methods used (and the press tool) will be

applicable for any future wheels introduced that use this design of axle.

Concept

The design features a taper joint between the wheel and axle. Tapers of a shallow enough angle, when pressed firmly

together, form a secure ‘locked’ joint which provides the kind of accurate location needed for a true-running wheelset.

No adhesive is needed in the taper joint and this means that the taper can be released and the wheels removed by

pressing the axle out of the centre of the wheel...... and then reassembled by pressing the wheel back on to the

tapered axle.

The difficulty with shallow-angle tapers is that the position at which they lock is very sensitive to small changes in the

dimensions of either of the components involved - a manufacturing nightmare if the aim is to make an axle with a

taper on both ends which will ensure both wheels are locked at the required back to back dimension.

Our solution is a three-part axle which is assembled by the modeller - this forming the first part of the assembly

sequence. We strongly advise that, when wheelsets are dismantled, care is taken to keep each axle with the wheels it

was initially assembled with.

This shows the cross-section of an assembled wheelset - the three-part axle and taper joints can be seen together

with the wheels with their bearing surfaces integral with the wheel. The grooves in the bearing surfaces are to assist

oil retention.

The press tool shown in cross-section below consists of a frame and screw with two small components - one to fit in

the frame (’A’) and one to fit on the screw (’B’). These enable the tool to be used in several different ways.

Assembling an Axle

An axle consists of a central metal sleeve with two plastic stub axles. This section describes how to assemble these to

produce an axle of the required length so that the taper joints will lock at the required back to back dimension.

First, prepare the stub axles. These are made of a special hard plastic (Torlon) and need care when they are being

detached from their sprue to avoid lifting the surface skin. Score the mould feed with a scalpel where shown in the

cross-section view below and break the stub axle from its sprue by bending in the direction shown. Use a scalpel to

clean off any remaining roughness that protrudes above the round surface of the stub axle.

Before going further, examine the wheels carefully to make sure that there is no mould sprue material sticking out

beyond the back face of the wheel rim. The mould is filled at a point on the back face of the wheel in line with the

crankpin boss, and it is here that you may find a small raised mould pip (see below). Trim it flush with the back of the

wheel with a scalpel.

Now put the other end of the stub axle in the removable anvil (component ‘A’) of the press tool and put component ‘A’

with the stub axle and wheel in position in the press tool frame as shown in the smaller picture below. Put the remov-

able sleeve ‘B’ in position on the end of the operating screw and screw the screw in until the end of ‘B’ engages in the

centre of the wheel, pressing on the metal centre boss, as shown below. Tighten the screw, making sure the end of ‘B’

is pressing on the metal boss and not the plastic moulding, and then tighten the screw very firmly - but using just

fingers on the screw knob - do not use other tools to get it even tighter.

Repeat all this for the other wheel and stub axle so that you have two wheels firmly locked on their stub axles.

Now to assemble the axle - and please note the following:

i) A dry run axle assembly is worth doing - the work needs to be completed reasonably quickly, before the Loctite sets;

ii) When using Loctite, avoid contact with the liquid and observe the safety instructions provided;

iii) Do not pay any attention at this stage to wheel quartering - that comes later.

Apply a small drop of Loctite 603 (or 638) to the surface near the inner end of one stub axle and spread it round the

circumference. Park the wheel while you put Loctite in one end of the axle sleeve (a more generous drop is OK here).

Now push the stub axle into the sleeve, twisting the sleeve to spread the Loctite evenly. Apply Loctite in the same way

to the other stub axle and into the other end of the sleeve and push the second stub axle into the sleeve, again

twisting the sleeve. Wipe surplus Loctite off with a tissue and place the wheelset in the back to back gauge.

With finger and thumb, hold the wheels against the gauge, pressing gently along the line of the axle. Using a small

screwdriver, adjust the position of the sleeve so that the gaps at each end between it and the inner ends of the wheel

bearing surfaces are the same on both sides. Continue holding the wheels in place for a few minutes and then leave

them standing for an hour or so - by which time the Loctite should have gone off sufficiently for the wheelset to be

removed from the gauge. Best to leave the wheelset overnight, though, before doing any more work on it.

You now have a wheelset that can be dismantled and reassembled, each time with the tapers locking at the correct

back to back dimension and with the wheels running true.

Working on the Wheelset

A range of further steps will be necessary before the wheelset will be installed in a working locomotive - including, for

example, fitting bearings, adjusting sideplay with washers, fitting crankpins, quartering (or whatever angle is appropri-

ate between the crankpins on opposite sides of your loco), fitting return cranks, fitting balance weights and so on.

Many of these require dismantling of the wheelset and for others, while dismantling may not be essential, it can make

the job easier. This section therefore covers dismantling and reassembling the wheelset.

First, a comment on loco design. To use the press tool to dismantle a wheelset, it is necessary for the wheelset first to

be removed from the loco chassis. Some kits and approaches to chassis design do not allow for this and it is suggested

that modifications are made so that removal is possible. Trying to dismantle a wheelset while it is still installed in a

chassis is likely to result in damage to the wheelset, chassis, or both.

To dismantle a wheelset, remove components ‘A’ and ‘B’ from the press tool and place the wheelset in the press tool as

shown on the left below.

Screw the operating screw in, making sure the narrow tip of the screw bears on the end of the plastic stub axle and

does not catch on the metal boss of the wheel - see the right-hand picture above. Tighten the screw until, quite

suddenly, the taper is released and the axle drops

out of the wheel boss. This should not need anything

more than firm finger pressure on the screw knob of

the operating screw. The procedure can be repeated

for the other wheel, though for most work on the

wheels, removing one wheel is likely to be sufficient.

A dismantled wheelset is shown on the right, with

the three-part axle in its final, assembled, form.

These instructions will not (for now, at least) cover most of the other work that might be done on the wheels - though

notes on crankpin assembly and quartering are included later. But once any work has been completed, the wheelset

will need to be reassembled, as follows.

Push each wheel boss onto its end of the axle, then gently squeeze the wheelset between thumb and forefinger (at

this point, the tapers will be binding sufficiently for the quartering to be tested - see next section). Place components

‘A’ and ‘B’ in position in the press tool, though this time with component ‘A’ reversed, with the solid end (which fits

inside the wheel moulding and engages with metal wheel boss) facing the operating screw.

When the wheelset has been assembled for the final time, axle caps (4DW 103) can be glued into the wheel centres to

give the proper axle end appearance. We suggest an adhesive that does not set too hard (possibly even Blutack) is

used to minimise the risk of damage if removal is eventually necessary.

Quartering

No special provision has been made for quartering and it is therefore necessary to do it by eye or make or obtain some

appropriate fixture. Remember, though, that it is not necessary to achieve an exact angle - just to get the same angle

on all the wheelsets.

The ability of the locking tapers between the wheels and axles to be ‘lightly locked’ with finger pressure, tested for free

running and then adjusted if necessary by simple twisting of the wheels may help. Final setting to the correct back to

back dimension (as above) would then only be done when satisfactory quartering has been achieved.

Take a wheel and stub axle, check that the taper of the

stub axle and the bore of the wheel are clean, and push

the taper section of the stub axle into the wheel so that

it is finger-tight - to give the result shown on the left.

Even at this stage, you should be able to feel some

locking effect between the stub axle and the wheel.

Place the wheelset in the press tool,

fitting the front face of one wheel

on component ‘A’ and screwing the

screw in until component ‘B’ sits in

the recess in the front face of the

other wheel, as shown on the left.

Do not tighten the scew further yet.

Now place a back to back gauge between the

wheels, as shown on the right. The back to back

gauge will rest conveniently on the press tool.

Tighten the screw so that the wheels are pressed

more tightly onto the tapered ends of the axle.

As you do this repeatedly check how easily the

back to back gauge moves up and down between

the wheels. At some point, the play between the

wheels and the gauge will be eliminated and the

wheels will just begin to bind on the gauge - this

is when the wheels are correctly gauged. Undo

the operating screw and remove the gauge and

wheelset. Check that the gauge still can slide

betwen the wheels without any play and then roll

the wheelset on a flat surface to confirm that the

wheels run true.

Crankpins

The Exactoscale crankpin range is based on M1 countersunk stainless steel screws, located in an aluminium insert that

fit in a recess moulded in the back of the driving wheel. A shouldered (’top hat’) threaded phosphor bronze bearing is

screwed onto the M1 screw, clamping the moulded wheel centre between the aluminium insert and the ‘top hat’

bearing. The cross-section drawing below shows these components.

To assemble a crankpin, first check the recess in the back of the wheel. It is important that there is nothing preventing

the aluminimum insert fitting correctly in the recess as otherwise it (and the screw head) will not be flush with the

back face of the wheel. It is also important not to deepen the recess as that could prevent the insert and the crankpin

bearing clamping the wheel moulding properly. Then push an aluminium insert into the recess, checking that it is flush

with the back of the wheel (see first drawing below). Take an M1 countersunk screw and check that there are no burrs

at the end of the slot in its head that could prevent it sitting correctly in the countersink. Use a needle file to remove

them if there are any. Push the M1 screw into the aluminium insert (see second drawing below).

Take a threaded crankpin bearing (reduce its length if it is too long for the thickness of the coupling rods being used)

and, holding the bearing surface in a pin chuck, screw it onto the M1 screw. If you are confident that the crankpin will

not need to be removed (or have its position adjusted to get a return crank correctly angled), put a drop of Thread-

locker (Loctite 243) on the screw before finally tightening it to clamp onto the moulded wheel centre. The third

drawing below shows the crankpin in position.

The Exactoscale range of crankpin components includes a threaded bearing extension, spacer washers and two sorts of

crankpin nut (round and hexagonal).

It may be possible to use the round crankpin nut reversed for the recessed nut that is sometimes needed on the

leading coupled wheels of an outside cylinder loco, though considerable thinning of the ‘top hat’ crankpin bearing will

probably be needed to give an acceptable overall crankpin length.

It may also be possible to use the threaded bearing extension to create a robust return crank. Thread a bearing

extension onto an M1 screw (right up to the head). Drill a 1.0mmØ hole in a thick piece of aluminium (or MDF might

do) and place the M1 screw in it - so keeping the bearing extension square to the surface of the aluminium/MDF. Open

out the return crank to 1.5mmØ and place it front face downwards over the bearing extension, then run a bead of

solder round the join between the return crank and bearing extension. Unscrew the M1 screw and screw the return

crank assembly tightly onto the crankpin, check its position and work out the amount of any angular adjustment

needed. Remove the return crank from the crankpin, loosen and retighten the cranpin having made the necessary

adjustment in the position of the screw slot and replace and retighten the return crank. It may take several attempts

but it should be possible using this method to get the return crank tight in the correct position.

As will be obvious, this section does not yet reflect much actual experience of using these components. It will be

extended and updated in due course. Feedback from modellers to help with this will be welcomed.

Crankpin bearing (4CR 603)

Plastic stub axle

Axle sleeve

Moulded wheel centre

Wheel rim

M1 screw (4CR 601)

Aluminium insert (4CR 602)

Axle cap (4DW 103)

Centre boss with

bearing surface

Frame

Operating screw

Removable sleeve ‘B’

Removable anvil ‘A’

Score here

Mould feed

Round

section

Taper

section

Stub axle

Location of mould pip (if any)

Removable anvil ‘A’

Removable sleeve ‘B’

Drop of Loctite here

Axle sleeve

Axle sleeve centred

between wheel bosses

Exactoscale Back to

Back gauge

M1 countersunk screw

Threaded crankpin bearing

Aluminium insert

Moulded wheel centre

Instructions for Assembling Driving Wheels, Axles and Crankpins

(Version 1; October 2008)

Introduction

These instructions explain how to assemble Exactoscale 4mm scale driving wheels, axles and crankpins to produce a

wheelset that is has the desired back to back setting, has wheels that run true and crankpins with a consistent throw.

The design features that help to achieve this result will only work properly if the correct assembly procedure is

followed. It is therefore important to read these instructions carefully and understand the reasons for the sequence

that is described.

Successful assembly of the wheels and axles (and subsequent removal of wheels from their axle) depends on the use

of a small press specifically designed for the purpose. Attempting to assemble or dismantle wheelsets without using

the press is likely to result in damage.

The drawings in these instructions show a 6’ 8” driving wheel but the methods used (and the press tool) will be

applicable for any future wheels introduced that use this design of axle.

Concept

The design features a taper joint between the wheel and axle. Tapers of a shallow enough angle, when pressed firmly

together, form a secure ‘locked’ joint which provides the kind of accurate location needed for a true-running wheelset.

No adhesive is needed in the taper joint and this means that the taper can be released and the wheels removed by

pressing the axle out of the centre of the wheel...... and then reassembled by pressing the wheel back on to the

tapered axle.

The difficulty with shallow-angle tapers is that the position at which they lock is very sensitive to small changes in the

dimensions of either of the components involved - a manufacturing nightmare if the aim is to make an axle with a

taper on both ends which will ensure both wheels are locked at the required back to back dimension.

Our solution is a three-part axle which is assembled by the modeller - this forming the first part of the assembly

sequence. We strongly advise that, when wheelsets are dismantled, care is taken to keep each axle with the wheels it

was initially assembled with.

This shows the cross-section of an assembled wheelset - the three-part axle and taper joints can be seen together

with the wheels with their bearing surfaces integral with the wheel. The grooves in the bearing surfaces are to assist

oil retention.

The press tool shown in cross-section below consists of a frame and screw with two small components - one to fit in

the frame (’A’) and one to fit on the screw (’B’). These enable the tool to be used in several different ways.

Assembling an Axle

An axle consists of a central metal sleeve with two plastic stub axles. This section describes how to assemble these to

produce an axle of the required length so that the taper joints will lock at the required back to back dimension.

First, prepare the stub axles. These are made of a special hard plastic (Torlon) and need care when they are being

detached from their sprue to avoid lifting the surface skin. Score the mould feed with a scalpel where shown in the

cross-section view below and break the stub axle from its sprue by bending in the direction shown. Use a scalpel to

clean off any remaining roughness that protrudes above the round surface of the stub axle.

Before going further, examine the wheels carefully to make sure that there is no mould sprue material sticking out

beyond the back face of the wheel rim. The mould is filled at a point on the back face of the wheel in line with the

crankpin boss, and it is here that you may find a small raised mould pip (see below). Trim it flush with the back of the

wheel with a scalpel.

Now put the other end of the stub axle in the removable anvil (component ‘A’) of the press tool and put component ‘A’

with the stub axle and wheel in position in the press tool frame as shown in the smaller picture below. Put the remov-

able sleeve ‘B’ in position on the end of the operating screw and screw the screw in until the end of ‘B’ engages in the

centre of the wheel, pressing on the metal centre boss, as shown below. Tighten the screw, making sure the end of ‘B’

is pressing on the metal boss and not the plastic moulding, and then tighten the screw very firmly - but using just

fingers on the screw knob - do not use other tools to get it even tighter.

Repeat all this for the other wheel and stub axle so that you have two wheels firmly locked on their stub axles.

Now to assemble the axle - and please note the following:

i) A dry run axle assembly is worth doing - the work needs to be completed reasonably quickly, before the Loctite sets;

ii) When using Loctite, avoid contact with the liquid and observe the safety instructions provided;

iii) Do not pay any attention at this stage to wheel quartering - that comes later.

Apply a small drop of Loctite 603 (or 638) to the surface near the inner end of one stub axle and spread it round the

circumference. Park the wheel while you put Loctite in one end of the axle sleeve (a more generous drop is OK here).

Now push the stub axle into the sleeve, twisting the sleeve to spread the Loctite evenly. Apply Loctite in the same way

to the other stub axle and into the other end of the sleeve and push the second stub axle into the sleeve, again

twisting the sleeve. Wipe surplus Loctite off with a tissue and place the wheelset in the back to back gauge.

With finger and thumb, hold the wheels against the gauge, pressing gently along the line of the axle. Using a small

screwdriver, adjust the position of the sleeve so that the gaps at each end between it and the inner ends of the wheel

bearing surfaces are the same on both sides. Continue holding the wheels in place for a few minutes and then leave

them standing for an hour or so - by which time the Loctite should have gone off sufficiently for the wheelset to be

removed from the gauge. Best to leave the wheelset overnight, though, before doing any more work on it.

You now have a wheelset that can be dismantled and reassembled, each time with the tapers locking at the correct

back to back dimension and with the wheels running true.

Working on the Wheelset

A range of further steps will be necessary before the wheelset will be installed in a working locomotive - including, for

example, fitting bearings, adjusting sideplay with washers, fitting crankpins, quartering (or whatever angle is appropri-

ate between the crankpins on opposite sides of your loco), fitting return cranks, fitting balance weights and so on.

Many of these require dismantling of the wheelset and for others, while dismantling may not be essential, it can make

the job easier. This section therefore covers dismantling and reassembling the wheelset.

First, a comment on loco design. To use the press tool to dismantle a wheelset, it is necessary for the wheelset first to

be removed from the loco chassis. Some kits and approaches to chassis design do not allow for this and it is suggested

that modifications are made so that removal is possible. Trying to dismantle a wheelset while it is still installed in a

chassis is likely to result in damage to the wheelset, chassis, or both.

To dismantle a wheelset, remove components ‘A’ and ‘B’ from the press tool and place the wheelset in the press tool as

shown on the left below.

Screw the operating screw in, making sure the narrow tip of the screw bears on the end of the plastic stub axle and

does not catch on the metal boss of the wheel - see the right-hand picture above. Tighten the screw until, quite

suddenly, the taper is released and the axle drops

out of the wheel boss. This should not need anything

more than firm finger pressure on the screw knob of

the operating screw. The procedure can be repeated

for the other wheel, though for most work on the

wheels, removing one wheel is likely to be sufficient.

A dismantled wheelset is shown on the right, with

the three-part axle in its final, assembled, form.

These instructions will not (for now, at least) cover most of the other work that might be done on the wheels - though

notes on crankpin assembly and quartering are included later. But once any work has been completed, the wheelset

will need to be reassembled, as follows.

Push each wheel boss onto its end of the axle, then gently squeeze the wheelset between thumb and forefinger (at

this point, the tapers will be binding sufficiently for the quartering to be tested - see next section). Place components

‘A’ and ‘B’ in position in the press tool, though this time with component ‘A’ reversed, with the solid end (which fits

inside the wheel moulding and engages with metal wheel boss) facing the operating screw.

When the wheelset has been assembled for the final time, axle caps (4DW 103) can be glued into the wheel centres to

give the proper axle end appearance. We suggest an adhesive that does not set too hard (possibly even Blutack) is

used to minimise the risk of damage if removal is eventually necessary.

Quartering

No special provision has been made for quartering and it is therefore necessary to do it by eye or make or obtain some

appropriate fixture. Remember, though, that it is not necessary to achieve an exact angle - just to get the same angle

on all the wheelsets.

The ability of the locking tapers between the wheels and axles to be ‘lightly locked’ with finger pressure, tested for free

running and then adjusted if necessary by simple twisting of the wheels may help. Final setting to the correct back to

back dimension (as above) would then only be done when satisfactory quartering has been achieved.

Take a wheel and stub axle, check that the taper of the

stub axle and the bore of the wheel are clean, and push

the taper section of the stub axle into the wheel so that

it is finger-tight - to give the result shown on the left.

Even at this stage, you should be able to feel some

locking effect between the stub axle and the wheel.

Place the wheelset in the press tool,

fitting the front face of one wheel

on component ‘A’ and screwing the

screw in until component ‘B’ sits in

the recess in the front face of the

other wheel, as shown on the left.

Do not tighten the scew further yet.

Now place a back to back gauge between the

wheels, as shown on the right. The back to back

gauge will rest conveniently on the press tool.

Tighten the screw so that the wheels are pressed

more tightly onto the tapered ends of the axle.

As you do this repeatedly check how easily the

back to back gauge moves up and down between

the wheels. At some point, the play between the

wheels and the gauge will be eliminated and the

wheels will just begin to bind on the gauge - this

is when the wheels are correctly gauged. Undo

the operating screw and remove the gauge and

wheelset. Check that the gauge still can slide

betwen the wheels without any play and then roll

the wheelset on a flat surface to confirm that the

wheels run true.

Crankpins

The Exactoscale crankpin range is based on M1 countersunk stainless steel screws, located in an aluminium insert that

fit in a recess moulded in the back of the driving wheel. A shouldered (’top hat’) threaded phosphor bronze bearing is

screwed onto the M1 screw, clamping the moulded wheel centre between the aluminium insert and the ‘top hat’

bearing. The cross-section drawing below shows these components.

To assemble a crankpin, first check the recess in the back of the wheel. It is important that there is nothing preventing

the aluminimum insert fitting correctly in the recess as otherwise it (and the screw head) will not be flush with the

back face of the wheel. It is also important not to deepen the recess as that could prevent the insert and the crankpin

bearing clamping the wheel moulding properly. Then push an aluminium insert into the recess, checking that it is flush

with the back of the wheel (see first drawing below). Take an M1 countersunk screw and check that there are no burrs

at the end of the slot in its head that could prevent it sitting correctly in the countersink. Use a needle file to remove

them if there are any. Push the M1 screw into the aluminium insert (see second drawing below).

Take a threaded crankpin bearing (reduce its length if it is too long for the thickness of the coupling rods being used)

and, holding the bearing surface in a pin chuck, screw it onto the M1 screw. If you are confident that the crankpin will

not need to be removed (or have its position adjusted to get a return crank correctly angled), put a drop of Thread-

locker (Loctite 243) on the screw before finally tightening it to clamp onto the moulded wheel centre. The third

drawing below shows the crankpin in position.

The Exactoscale range of crankpin components includes a threaded bearing extension, spacer washers and two sorts of

crankpin nut (round and hexagonal).

It may be possible to use the round crankpin nut reversed for the recessed nut that is sometimes needed on the

leading coupled wheels of an outside cylinder loco, though considerable thinning of the ‘top hat’ crankpin bearing will

probably be needed to give an acceptable overall crankpin length.

It may also be possible to use the threaded bearing extension to create a robust return crank. Thread a bearing

extension onto an M1 screw (right up to the head). Drill a 1.0mmØ hole in a thick piece of aluminium (or MDF might

do) and place the M1 screw in it - so keeping the bearing extension square to the surface of the aluminium/MDF. Open

out the return crank to 1.5mmØ and place it front face downwards over the bearing extension, then run a bead of

solder round the join between the return crank and bearing extension. Unscrew the M1 screw and screw the return

crank assembly tightly onto the crankpin, check its position and work out the amount of any angular adjustment

needed. Remove the return crank from the crankpin, loosen and retighten the cranpin having made the necessary

adjustment in the position of the screw slot and replace and retighten the return crank. It may take several attempts

but it should be possible using this method to get the return crank tight in the correct position.

As will be obvious, this section does not yet reflect much actual experience of using these components. It will be

extended and updated in due course. Feedback from modellers to help with this will be welcomed.

Crankpin bearing (4CR 603)

Plastic stub axle

Axle sleeve

Moulded wheel centre

Wheel rim

M1 screw (4CR 601)

Aluminium insert (4CR 602)

Axle cap (4DW 103)

Centre boss with

bearing surface

Frame

Operating screw

Removable sleeve ‘B’

Removable anvil ‘A’

Score here

Mould feed

Round

section

Taper

section

Stub axle

Location of mould pip (if any)

Removable anvil ‘A’

Removable sleeve ‘B’

Drop of Loctite here

Axle sleeve

Axle sleeve centred

between wheel bosses

Exactoscale Back to

Back gauge

M1 countersunk screw

Threaded crankpin bearing

Aluminium insert

Moulded wheel centre

Instructions for Assembling Driving Wheels, Axles and Crankpins

(Version 1; October 2008)

Introduction

These instructions explain how to assemble Exactoscale 4mm scale driving wheels, axles and crankpins to produce a

wheelset that is has the desired back to back setting, has wheels that run true and crankpins with a consistent throw.

The design features that help to achieve this result will only work properly if the correct assembly procedure is

followed. It is therefore important to read these instructions carefully and understand the reasons for the sequence

that is described.

Successful assembly of the wheels and axles (and subsequent removal of wheels from their axle) depends on the use

of a small press specifically designed for the purpose. Attempting to assemble or dismantle wheelsets without using

the press is likely to result in damage.

The drawings in these instructions show a 6’ 8” driving wheel but the methods used (and the press tool) will be

applicable for any future wheels introduced that use this design of axle.

Concept

The design features a taper joint between the wheel and axle. Tapers of a shallow enough angle, when pressed firmly

together, form a secure ‘locked’ joint which provides the kind of accurate location needed for a true-running wheelset.

No adhesive is needed in the taper joint and this means that the taper can be released and the wheels removed by

pressing the axle out of the centre of the wheel...... and then reassembled by pressing the wheel back on to the

tapered axle.

The difficulty with shallow-angle tapers is that the position at which they lock is very sensitive to small changes in the

dimensions of either of the components involved - a manufacturing nightmare if the aim is to make an axle with a

taper on both ends which will ensure both wheels are locked at the required back to back dimension.

Our solution is a three-part axle which is assembled by the modeller - this forming the first part of the assembly

sequence. We strongly advise that, when wheelsets are dismantled, care is taken to keep each axle with the wheels it

was initially assembled with.

This shows the cross-section of an assembled wheelset - the three-part axle and taper joints can be seen together

with the wheels with their bearing surfaces integral with the wheel. The grooves in the bearing surfaces are to assist

oil retention.

The press tool shown in cross-section below consists of a frame and screw with two small components - one to fit in

the frame (’A’) and one to fit on the screw (’B’). These enable the tool to be used in several different ways.

Assembling an Axle

An axle consists of a central metal sleeve with two plastic stub axles. This section describes how to assemble these to

produce an axle of the required length so that the taper joints will lock at the required back to back dimension.

First, prepare the stub axles. These are made of a special hard plastic (Torlon) and need care when they are being

detached from their sprue to avoid lifting the surface skin. Score the mould feed with a scalpel where shown in the

cross-section view below and break the stub axle from its sprue by bending in the direction shown. Use a scalpel to

clean off any remaining roughness that protrudes above the round surface of the stub axle.

Before going further, examine the wheels carefully to make sure that there is no mould sprue material sticking out

beyond the back face of the wheel rim. The mould is filled at a point on the back face of the wheel in line with the

crankpin boss, and it is here that you may find a small raised mould pip (see below). Trim it flush with the back of the

wheel with a scalpel.

Now put the other end of the stub axle in the removable anvil (component ‘A’) of the press tool and put component ‘A’

with the stub axle and wheel in position in the press tool frame as shown in the smaller picture below. Put the remov-

able sleeve ‘B’ in position on the end of the operating screw and screw the screw in until the end of ‘B’ engages in the

centre of the wheel, pressing on the metal centre boss, as shown below. Tighten the screw, making sure the end of ‘B’

is pressing on the metal boss and not the plastic moulding, and then tighten the screw very firmly - but using just

fingers on the screw knob - do not use other tools to get it even tighter.

Repeat all this for the other wheel and stub axle so that you have two wheels firmly locked on their stub axles.

Now to assemble the axle - and please note the following:

i) A dry run axle assembly is worth doing - the work needs to be completed reasonably quickly, before the Loctite sets;

ii) When using Loctite, avoid contact with the liquid and observe the safety instructions provided;

iii) Do not pay any attention at this stage to wheel quartering - that comes later.

Apply a small drop of Loctite 603 (or 638) to the surface near the inner end of one stub axle and spread it round the

circumference. Park the wheel while you put Loctite in one end of the axle sleeve (a more generous drop is OK here).

Now push the stub axle into the sleeve, twisting the sleeve to spread the Loctite evenly. Apply Loctite in the same way

to the other stub axle and into the other end of the sleeve and push the second stub axle into the sleeve, again

twisting the sleeve. Wipe surplus Loctite off with a tissue and place the wheelset in the back to back gauge.

With finger and thumb, hold the wheels against the gauge, pressing gently along the line of the axle. Using a small

screwdriver, adjust the position of the sleeve so that the gaps at each end between it and the inner ends of the wheel

bearing surfaces are the same on both sides. Continue holding the wheels in place for a few minutes and then leave

them standing for an hour or so - by which time the Loctite should have gone off sufficiently for the wheelset to be

removed from the gauge. Best to leave the wheelset overnight, though, before doing any more work on it.

You now have a wheelset that can be dismantled and reassembled, each time with the tapers locking at the correct

back to back dimension and with the wheels running true.

Working on the Wheelset

A range of further steps will be necessary before the wheelset will be installed in a working locomotive - including, for

example, fitting bearings, adjusting sideplay with washers, fitting crankpins, quartering (or whatever angle is appropri-

ate between the crankpins on opposite sides of your loco), fitting return cranks, fitting balance weights and so on.

Many of these require dismantling of the wheelset and for others, while dismantling may not be essential, it can make

the job easier. This section therefore covers dismantling and reassembling the wheelset.

First, a comment on loco design. To use the press tool to dismantle a wheelset, it is necessary for the wheelset first to

be removed from the loco chassis. Some kits and approaches to chassis design do not allow for this and it is suggested

that modifications are made so that removal is possible. Trying to dismantle a wheelset while it is still installed in a

chassis is likely to result in damage to the wheelset, chassis, or both.

To dismantle a wheelset, remove components ‘A’ and ‘B’ from the press tool and place the wheelset in the press tool as

shown on the left below.

Screw the operating screw in, making sure the narrow tip of the screw bears on the end of the plastic stub axle and

does not catch on the metal boss of the wheel - see the right-hand picture above. Tighten the screw until, quite

suddenly, the taper is released and the axle drops

out of the wheel boss. This should not need anything

more than firm finger pressure on the screw knob of

the operating screw. The procedure can be repeated

for the other wheel, though for most work on the

wheels, removing one wheel is likely to be sufficient.

A dismantled wheelset is shown on the right, with

the three-part axle in its final, assembled, form.

These instructions will not (for now, at least) cover most of the other work that might be done on the wheels - though

notes on crankpin assembly and quartering are included later. But once any work has been completed, the wheelset

will need to be reassembled, as follows.

Push each wheel boss onto its end of the axle, then gently squeeze the wheelset between thumb and forefinger (at

this point, the tapers will be binding sufficiently for the quartering to be tested - see next section). Place components

‘A’ and ‘B’ in position in the press tool, though this time with component ‘A’ reversed, with the solid end (which fits

inside the wheel moulding and engages with metal wheel boss) facing the operating screw.

When the wheelset has been assembled for the final time, axle caps (4DW 103) can be glued into the wheel centres to

give the proper axle end appearance. We suggest an adhesive that does not set too hard (possibly even Blutack) is

used to minimise the risk of damage if removal is eventually necessary.

Quartering

No special provision has been made for quartering and it is therefore necessary to do it by eye or make or obtain some

appropriate fixture. Remember, though, that it is not necessary to achieve an exact angle - just to get the same angle

on all the wheelsets.

The ability of the locking tapers between the wheels and axles to be ‘lightly locked’ with finger pressure, tested for free

running and then adjusted if necessary by simple twisting of the wheels may help. Final setting to the correct back to

back dimension (as above) would then only be done when satisfactory quartering has been achieved.

Take a wheel and stub axle, check that the taper of the

stub axle and the bore of the wheel are clean, and push

the taper section of the stub axle into the wheel so that

it is finger-tight - to give the result shown on the left.

Even at this stage, you should be able to feel some

locking effect between the stub axle and the wheel.

Place the wheelset in the press tool,

fitting the front face of one wheel

on component ‘A’ and screwing the

screw in until component ‘B’ sits in

the recess in the front face of the

other wheel, as shown on the left.

Do not tighten the scew further yet.

Now place a back to back gauge between the

wheels, as shown on the right. The back to back

gauge will rest conveniently on the press tool.

Tighten the screw so that the wheels are pressed

more tightly onto the tapered ends of the axle.

As you do this repeatedly check how easily the

back to back gauge moves up and down between

the wheels. At some point, the play between the

wheels and the gauge will be eliminated and the

wheels will just begin to bind on the gauge - this

is when the wheels are correctly gauged. Undo

the operating screw and remove the gauge and

wheelset. Check that the gauge still can slide

betwen the wheels without any play and then roll

the wheelset on a flat surface to confirm that the

wheels run true.

Crankpins

The Exactoscale crankpin range is based on M1 countersunk stainless steel screws, located in an aluminium insert that

fit in a recess moulded in the back of the driving wheel. A shouldered (’top hat’) threaded phosphor bronze bearing is

screwed onto the M1 screw, clamping the moulded wheel centre between the aluminium insert and the ‘top hat’

bearing. The cross-section drawing below shows these components.

To assemble a crankpin, first check the recess in the back of the wheel. It is important that there is nothing preventing

the aluminimum insert fitting correctly in the recess as otherwise it (and the screw head) will not be flush with the

back face of the wheel. It is also important not to deepen the recess as that could prevent the insert and the crankpin

bearing clamping the wheel moulding properly. Then push an aluminium insert into the recess, checking that it is flush

with the back of the wheel (see first drawing below). Take an M1 countersunk screw and check that there are no burrs

at the end of the slot in its head that could prevent it sitting correctly in the countersink. Use a needle file to remove

them if there are any. Push the M1 screw into the aluminium insert (see second drawing below).

Take a threaded crankpin bearing (reduce its length if it is too long for the thickness of the coupling rods being used)

and, holding the bearing surface in a pin chuck, screw it onto the M1 screw. If you are confident that the crankpin will

not need to be removed (or have its position adjusted to get a return crank correctly angled), put a drop of Thread-

locker (Loctite 243) on the screw before finally tightening it to clamp onto the moulded wheel centre. The third

drawing below shows the crankpin in position.

The Exactoscale range of crankpin components includes a threaded bearing extension, spacer washers and two sorts of

crankpin nut (round and hexagonal).

It may be possible to use the round crankpin nut reversed for the recessed nut that is sometimes needed on the

leading coupled wheels of an outside cylinder loco, though considerable thinning of the ‘top hat’ crankpin bearing will

probably be needed to give an acceptable overall crankpin length.

It may also be possible to use the threaded bearing extension to create a robust return crank. Thread a bearing

extension onto an M1 screw (right up to the head). Drill a 1.0mmØ hole in a thick piece of aluminium (or MDF might

do) and place the M1 screw in it - so keeping the bearing extension square to the surface of the aluminium/MDF. Open

out the return crank to 1.5mmØ and place it front face downwards over the bearing extension, then run a bead of

solder round the join between the return crank and bearing extension. Unscrew the M1 screw and screw the return

crank assembly tightly onto the crankpin, check its position and work out the amount of any angular adjustment

needed. Remove the return crank from the crankpin, loosen and retighten the cranpin having made the necessary

adjustment in the position of the screw slot and replace and retighten the return crank. It may take several attempts

but it should be possible using this method to get the return crank tight in the correct position.

As will be obvious, this section does not yet reflect much actual experience of using these components. It will be

extended and updated in due course. Feedback from modellers to help with this will be welcomed.

Crankpin bearing (4CR 603)

Plastic stub axle

Axle sleeve

Moulded wheel centre

Wheel rim

M1 screw (4CR 601)

Aluminium insert (4CR 602)

Axle cap (4DW 103)

Centre boss with

bearing surface

Frame

Operating screw

Removable sleeve ‘B’

Removable anvil ‘A’

Score here

Mould feed

Round

section

Taper

section

Stub axle

Location of mould pip (if any)

Removable anvil ‘A’

Removable sleeve ‘B’

Drop of Loctite here

Axle sleeve

Axle sleeve centred

between wheel bosses

Exactoscale Back to

Back gauge

M1 countersunk screw

Threaded crankpin bearing

Aluminium insert

Moulded wheel centre

Instructions for Assembling Driving Wheels, Axles and Crankpins

(Version 1; October 2008)

Introduction

These instructions explain how to assemble Exactoscale 4mm scale driving wheels, axles and crankpins to produce a

wheelset that is has the desired back to back setting, has wheels that run true and crankpins with a consistent throw.

The design features that help to achieve this result will only work properly if the correct assembly procedure is

followed. It is therefore important to read these instructions carefully and understand the reasons for the sequence

that is described.

Successful assembly of the wheels and axles (and subsequent removal of wheels from their axle) depends on the use

of a small press specifically designed for the purpose. Attempting to assemble or dismantle wheelsets without using

the press is likely to result in damage.

The drawings in these instructions show a 6’ 8” driving wheel but the methods used (and the press tool) will be

applicable for any future wheels introduced that use this design of axle.

Concept

The design features a taper joint between the wheel and axle. Tapers of a shallow enough angle, when pressed firmly

together, form a secure ‘locked’ joint which provides the kind of accurate location needed for a true-running wheelset.

No adhesive is needed in the taper joint and this means that the taper can be released and the wheels removed by

pressing the axle out of the centre of the wheel...... and then reassembled by pressing the wheel back on to the

tapered axle.

The difficulty with shallow-angle tapers is that the position at which they lock is very sensitive to small changes in the

dimensions of either of the components involved - a manufacturing nightmare if the aim is to make an axle with a

taper on both ends which will ensure both wheels are locked at the required back to back dimension.

Our solution is a three-part axle which is assembled by the modeller - this forming the first part of the assembly

sequence. We strongly advise that, when wheelsets are dismantled, care is taken to keep each axle with the wheels it

was initially assembled with.

This shows the cross-section of an assembled wheelset - the three-part axle and taper joints can be seen together

with the wheels with their bearing surfaces integral with the wheel. The grooves in the bearing surfaces are to assist

oil retention.

The press tool shown in cross-section below consists of a frame and screw with two small components - one to fit in

the frame (’A’) and one to fit on the screw (’B’). These enable the tool to be used in several different ways.

Assembling an Axle

An axle consists of a central metal sleeve with two plastic stub axles. This section describes how to assemble these to

produce an axle of the required length so that the taper joints will lock at the required back to back dimension.

First, prepare the stub axles. These are made of a special hard plastic (Torlon) and need care when they are being

detached from their sprue to avoid lifting the surface skin. Score the mould feed with a scalpel where shown in the

cross-section view below and break the stub axle from its sprue by bending in the direction shown. Use a scalpel to

clean off any remaining roughness that protrudes above the round surface of the stub axle.

Before going further, examine the wheels carefully to make sure that there is no mould sprue material sticking out

beyond the back face of the wheel rim. The mould is filled at a point on the back face of the wheel in line with the

crankpin boss, and it is here that you may find a small raised mould pip (see below). Trim it flush with the back of the

wheel with a scalpel.

Now put the other end of the stub axle in the removable anvil (component ‘A’) of the press tool and put component ‘A’

with the stub axle and wheel in position in the press tool frame as shown in the smaller picture below. Put the remov-

able sleeve ‘B’ in position on the end of the operating screw and screw the screw in until the end of ‘B’ engages in the

centre of the wheel, pressing on the metal centre boss, as shown below. Tighten the screw, making sure the end of ‘B’

is pressing on the metal boss and not the plastic moulding, and then tighten the screw very firmly - but using just

fingers on the screw knob - do not use other tools to get it even tighter.

Repeat all this for the other wheel and stub axle so that you have two wheels firmly locked on their stub axles.

Now to assemble the axle - and please note the following:

i) A dry run axle assembly is worth doing - the work needs to be completed reasonably quickly, before the Loctite sets;

ii) When using Loctite, avoid contact with the liquid and observe the safety instructions provided;

iii) Do not pay any attention at this stage to wheel quartering - that comes later.

Apply a small drop of Loctite 603 (or 638) to the surface near the inner end of one stub axle and spread it round the

circumference. Park the wheel while you put Loctite in one end of the axle sleeve (a more generous drop is OK here).

Now push the stub axle into the sleeve, twisting the sleeve to spread the Loctite evenly. Apply Loctite in the same way

to the other stub axle and into the other end of the sleeve and push the second stub axle into the sleeve, again

twisting the sleeve. Wipe surplus Loctite off with a tissue and place the wheelset in the back to back gauge.

With finger and thumb, hold the wheels against the gauge, pressing gently along the line of the axle. Using a small

screwdriver, adjust the position of the sleeve so that the gaps at each end between it and the inner ends of the wheel

bearing surfaces are the same on both sides. Continue holding the wheels in place for a few minutes and then leave

them standing for an hour or so - by which time the Loctite should have gone off sufficiently for the wheelset to be

removed from the gauge. Best to leave the wheelset overnight, though, before doing any more work on it.

You now have a wheelset that can be dismantled and reassembled, each time with the tapers locking at the correct

back to back dimension and with the wheels running true.

Working on the Wheelset

A range of further steps will be necessary before the wheelset will be installed in a working locomotive - including, for

example, fitting bearings, adjusting sideplay with washers, fitting crankpins, quartering (or whatever angle is appropri-

ate between the crankpins on opposite sides of your loco), fitting return cranks, fitting balance weights and so on.

Many of these require dismantling of the wheelset and for others, while dismantling may not be essential, it can make

the job easier. This section therefore covers dismantling and reassembling the wheelset.

First, a comment on loco design. To use the press tool to dismantle a wheelset, it is necessary for the wheelset first to

be removed from the loco chassis. Some kits and approaches to chassis design do not allow for this and it is suggested

that modifications are made so that removal is possible. Trying to dismantle a wheelset while it is still installed in a

chassis is likely to result in damage to the wheelset, chassis, or both.

To dismantle a wheelset, remove components ‘A’ and ‘B’ from the press tool and place the wheelset in the press tool as

shown on the left below.

Screw the operating screw in, making sure the narrow tip of the screw bears on the end of the plastic stub axle and

does not catch on the metal boss of the wheel - see the right-hand picture above. Tighten the screw until, quite

suddenly, the taper is released and the axle drops

out of the wheel boss. This should not need anything

more than firm finger pressure on the screw knob of

the operating screw. The procedure can be repeated

for the other wheel, though for most work on the

wheels, removing one wheel is likely to be sufficient.

A dismantled wheelset is shown on the right, with

the three-part axle in its final, assembled, form.

These instructions will not (for now, at least) cover most of the other work that might be done on the wheels - though

notes on crankpin assembly and quartering are included later. But once any work has been completed, the wheelset

will need to be reassembled, as follows.

Push each wheel boss onto its end of the axle, then gently squeeze the wheelset between thumb and forefinger (at

this point, the tapers will be binding sufficiently for the quartering to be tested - see next section). Place components

‘A’ and ‘B’ in position in the press tool, though this time with component ‘A’ reversed, with the solid end (which fits

inside the wheel moulding and engages with metal wheel boss) facing the operating screw.

When the wheelset has been assembled for the final time, axle caps (4DW 103) can be glued into the wheel centres to

give the proper axle end appearance. We suggest an adhesive that does not set too hard (possibly even Blutack) is

used to minimise the risk of damage if removal is eventually necessary.

Quartering

No special provision has been made for quartering and it is therefore necessary to do it by eye or make or obtain some

appropriate fixture. Remember, though, that it is not necessary to achieve an exact angle - just to get the same angle

on all the wheelsets.

The ability of the locking tapers between the wheels and axles to be ‘lightly locked’ with finger pressure, tested for free

running and then adjusted if necessary by simple twisting of the wheels may help. Final setting to the correct back to

back dimension (as above) would then only be done when satisfactory quartering has been achieved.

Take a wheel and stub axle, check that the taper of the

stub axle and the bore of the wheel are clean, and push

the taper section of the stub axle into the wheel so that

it is finger-tight - to give the result shown on the left.

Even at this stage, you should be able to feel some

locking effect between the stub axle and the wheel.

Place the wheelset in the press tool,

fitting the front face of one wheel

on component ‘A’ and screwing the

screw in until component ‘B’ sits in

the recess in the front face of the

other wheel, as shown on the left.

Do not tighten the scew further yet.

Now place a back to back gauge between the

wheels, as shown on the right. The back to back

gauge will rest conveniently on the press tool.

Tighten the screw so that the wheels are pressed

more tightly onto the tapered ends of the axle.

As you do this repeatedly check how easily the

back to back gauge moves up and down between

the wheels. At some point, the play between the

wheels and the gauge will be eliminated and the

wheels will just begin to bind on the gauge - this

is when the wheels are correctly gauged. Undo

the operating screw and remove the gauge and

wheelset. Check that the gauge still can slide

betwen the wheels without any play and then roll

the wheelset on a flat surface to confirm that the

wheels run true.

Crankpins

The Exactoscale crankpin range is based on M1 countersunk stainless steel screws, located in an aluminium insert that

fit in a recess moulded in the back of the driving wheel. A shouldered (’top hat’) threaded phosphor bronze bearing is

screwed onto the M1 screw, clamping the moulded wheel centre between the aluminium insert and the ‘top hat’

bearing. The cross-section drawing below shows these components.

To assemble a crankpin, first check the recess in the back of the wheel. It is important that there is nothing preventing

the aluminimum insert fitting correctly in the recess as otherwise it (and the screw head) will not be flush with the

back face of the wheel. It is also important not to deepen the recess as that could prevent the insert and the crankpin

bearing clamping the wheel moulding properly. Then push an aluminium insert into the recess, checking that it is flush

with the back of the wheel (see first drawing below). Take an M1 countersunk screw and check that there are no burrs

at the end of the slot in its head that could prevent it sitting correctly in the countersink. Use a needle file to remove

them if there are any. Push the M1 screw into the aluminium insert (see second drawing below).

Take a threaded crankpin bearing (reduce its length if it is too long for the thickness of the coupling rods being used)

and, holding the bearing surface in a pin chuck, screw it onto the M1 screw. If you are confident that the crankpin will

not need to be removed (or have its position adjusted to get a return crank correctly angled), put a drop of Thread-

locker (Loctite 243) on the screw before finally tightening it to clamp onto the moulded wheel centre. The third

drawing below shows the crankpin in position.

The Exactoscale range of crankpin components includes a threaded bearing extension, spacer washers and two sorts of

crankpin nut (round and hexagonal).

It may be possible to use the round crankpin nut reversed for the recessed nut that is sometimes needed on the

leading coupled wheels of an outside cylinder loco, though considerable thinning of the ‘top hat’ crankpin bearing will

probably be needed to give an acceptable overall crankpin length.

It may also be possible to use the threaded bearing extension to create a robust return crank. Thread a bearing

extension onto an M1 screw (right up to the head). Drill a 1.0mmØ hole in a thick piece of aluminium (or MDF might

do) and place the M1 screw in it - so keeping the bearing extension square to the surface of the aluminium/MDF. Open

out the return crank to 1.5mmØ and place it front face downwards over the bearing extension, then run a bead of

solder round the join between the return crank and bearing extension. Unscrew the M1 screw and screw the return

crank assembly tightly onto the crankpin, check its position and work out the amount of any angular adjustment

needed. Remove the return crank from the crankpin, loosen and retighten the cranpin having made the necessary

adjustment in the position of the screw slot and replace and retighten the return crank. It may take several attempts

but it should be possible using this method to get the return crank tight in the correct position.

As will be obvious, this section does not yet reflect much actual experience of using these components. It will be

extended and updated in due course. Feedback from modellers to help with this will be welcomed.

Crankpin bearing (4CR 603)

Plastic stub axle

Axle sleeve

Moulded wheel centre

Wheel rim

M1 screw (4CR 601)

Aluminium insert (4CR 602)

Axle cap (4DW 103)

Centre boss with

bearing surface

Frame

Operating screw

Removable sleeve ‘B’

Removable anvil ‘A’

Score here

Mould feed

Round

section

Taper

section

Stub axle

Location of mould pip (if any)

Removable anvil ‘A’

Removable sleeve ‘B’

Drop of Loctite here

Axle sleeve

Axle sleeve centred

between wheel bosses

Exactoscale Back to

Back gauge

M1 countersunk screw

Threaded crankpin bearing

Aluminium insert

Moulded wheel centre

Instructions for Assembling Driving Wheels, Axles and Crankpins

(Version 1; October 2008)

Introduction

These instructions explain how to assemble Exactoscale 4mm scale driving wheels, axles and crankpins to produce a

wheelset that is has the desired back to back setting, has wheels that run true and crankpins with a consistent throw.

The design features that help to achieve this result will only work properly if the correct assembly procedure is

followed. It is therefore important to read these instructions carefully and understand the reasons for the sequence

that is described.

Successful assembly of the wheels and axles (and subsequent removal of wheels from their axle) depends on the use

of a small press specifically designed for the purpose. Attempting to assemble or dismantle wheelsets without using

the press is likely to result in damage.

The drawings in these instructions show a 6’ 8” driving wheel but the methods used (and the press tool) will be

applicable for any future wheels introduced that use this design of axle.

Concept

The design features a taper joint between the wheel and axle. Tapers of a shallow enough angle, when pressed firmly

together, form a secure ‘locked’ joint which provides the kind of accurate location needed for a true-running wheelset.

No adhesive is needed in the taper joint and this means that the taper can be released and the wheels removed by

pressing the axle out of the centre of the wheel...... and then reassembled by pressing the wheel back on to the

tapered axle.

The difficulty with shallow-angle tapers is that the position at which they lock is very sensitive to small changes in the

dimensions of either of the components involved - a manufacturing nightmare if the aim is to make an axle with a

taper on both ends which will ensure both wheels are locked at the required back to back dimension.

Our solution is a three-part axle which is assembled by the modeller - this forming the first part of the assembly

sequence. We strongly advise that, when wheelsets are dismantled, care is taken to keep each axle with the wheels it

was initially assembled with.

This shows the cross-section of an assembled wheelset - the three-part axle and taper joints can be seen together

with the wheels with their bearing surfaces integral with the wheel. The grooves in the bearing surfaces are to assist

oil retention.

The press tool shown in cross-section below consists of a frame and screw with two small components - one to fit in

the frame (’A’) and one to fit on the screw (’B’). These enable the tool to be used in several different ways.

Assembling an Axle

An axle consists of a central metal sleeve with two plastic stub axles. This section describes how to assemble these to

produce an axle of the required length so that the taper joints will lock at the required back to back dimension.

First, prepare the stub axles. These are made of a special hard plastic (Torlon) and need care when they are being

detached from their sprue to avoid lifting the surface skin. Score the mould feed with a scalpel where shown in the

cross-section view below and break the stub axle from its sprue by bending in the direction shown. Use a scalpel to

clean off any remaining roughness that protrudes above the round surface of the stub axle.

Before going further, examine the wheels carefully to make sure that there is no mould sprue material sticking out

beyond the back face of the wheel rim. The mould is filled at a point on the back face of the wheel in line with the

crankpin boss, and it is here that you may find a small raised mould pip (see below). Trim it flush with the back of the

wheel with a scalpel.

Now put the other end of the stub axle in the removable anvil (component ‘A’) of the press tool and put component ‘A’

with the stub axle and wheel in position in the press tool frame as shown in the smaller picture below. Put the remov-

able sleeve ‘B’ in position on the end of the operating screw and screw the screw in until the end of ‘B’ engages in the

centre of the wheel, pressing on the metal centre boss, as shown below. Tighten the screw, making sure the end of ‘B’

is pressing on the metal boss and not the plastic moulding, and then tighten the screw very firmly - but using just

fingers on the screw knob - do not use other tools to get it even tighter.

Repeat all this for the other wheel and stub axle so that you have two wheels firmly locked on their stub axles.

Now to assemble the axle - and please note the following:

i) A dry run axle assembly is worth doing - the work needs to be completed reasonably quickly, before the Loctite sets;

ii) When using Loctite, avoid contact with the liquid and observe the safety instructions provided;

iii) Do not pay any attention at this stage to wheel quartering - that comes later.

Apply a small drop of Loctite 603 (or 638) to the surface near the inner end of one stub axle and spread it round the

circumference. Park the wheel while you put Loctite in one end of the axle sleeve (a more generous drop is OK here).

Now push the stub axle into the sleeve, twisting the sleeve to spread the Loctite evenly. Apply Loctite in the same way

to the other stub axle and into the other end of the sleeve and push the second stub axle into the sleeve, again

twisting the sleeve. Wipe surplus Loctite off with a tissue and place the wheelset in the back to back gauge.

With finger and thumb, hold the wheels against the gauge, pressing gently along the line of the axle. Using a small

screwdriver, adjust the position of the sleeve so that the gaps at each end between it and the inner ends of the wheel

bearing surfaces are the same on both sides. Continue holding the wheels in place for a few minutes and then leave

them standing for an hour or so - by which time the Loctite should have gone off sufficiently for the wheelset to be

removed from the gauge. Best to leave the wheelset overnight, though, before doing any more work on it.

You now have a wheelset that can be dismantled and reassembled, each time with the tapers locking at the correct

back to back dimension and with the wheels running true.

Working on the Wheelset

A range of further steps will be necessary before the wheelset will be installed in a working locomotive - including, for

example, fitting bearings, adjusting sideplay with washers, fitting crankpins, quartering (or whatever angle is appropri-

ate between the crankpins on opposite sides of your loco), fitting return cranks, fitting balance weights and so on.

Many of these require dismantling of the wheelset and for others, while dismantling may not be essential, it can make

the job easier. This section therefore covers dismantling and reassembling the wheelset.

First, a comment on loco design. To use the press tool to dismantle a wheelset, it is necessary for the wheelset first to

be removed from the loco chassis. Some kits and approaches to chassis design do not allow for this and it is suggested

that modifications are made so that removal is possible. Trying to dismantle a wheelset while it is still installed in a

chassis is likely to result in damage to the wheelset, chassis, or both.

To dismantle a wheelset, remove components ‘A’ and ‘B’ from the press tool and place the wheelset in the press tool as

shown on the left below.

Screw the operating screw in, making sure the narrow tip of the screw bears on the end of the plastic stub axle and

does not catch on the metal boss of the wheel - see the right-hand picture above. Tighten the screw until, quite

suddenly, the taper is released and the axle drops

out of the wheel boss. This should not need anything

more than firm finger pressure on the screw knob of

the operating screw. The procedure can be repeated

for the other wheel, though for most work on the

wheels, removing one wheel is likely to be sufficient.

A dismantled wheelset is shown on the right, with

the three-part axle in its final, assembled, form.

These instructions will not (for now, at least) cover most of the other work that might be done on the wheels - though

notes on crankpin assembly and quartering are included later. But once any work has been completed, the wheelset

will need to be reassembled, as follows.

Push each wheel boss onto its end of the axle, then gently squeeze the wheelset between thumb and forefinger (at

this point, the tapers will be binding sufficiently for the quartering to be tested - see next section). Place components

‘A’ and ‘B’ in position in the press tool, though this time with component ‘A’ reversed, with the solid end (which fits

inside the wheel moulding and engages with metal wheel boss) facing the operating screw.

When the wheelset has been assembled for the final time, axle caps (4DW 103) can be glued into the wheel centres to

give the proper axle end appearance. We suggest an adhesive that does not set too hard (possibly even Blutack) is

used to minimise the risk of damage if removal is eventually necessary.

Quartering

No special provision has been made for quartering and it is therefore necessary to do it by eye or make or obtain some

appropriate fixture. Remember, though, that it is not necessary to achieve an exact angle - just to get the same angle

on all the wheelsets.

The ability of the locking tapers between the wheels and axles to be ‘lightly locked’ with finger pressure, tested for free

running and then adjusted if necessary by simple twisting of the wheels may help. Final setting to the correct back to

back dimension (as above) would then only be done when satisfactory quartering has been achieved.

Take a wheel and stub axle, check that the taper of the

stub axle and the bore of the wheel are clean, and push

the taper section of the stub axle into the wheel so that

it is finger-tight - to give the result shown on the left.

Even at this stage, you should be able to feel some

locking effect between the stub axle and the wheel.

Place the wheelset in the press tool,

fitting the front face of one wheel

on component ‘A’ and screwing the

screw in until component ‘B’ sits in

the recess in the front face of the

other wheel, as shown on the left.

Do not tighten the scew further yet.

Now place a back to back gauge between the

wheels, as shown on the right. The back to back

gauge will rest conveniently on the press tool.

Tighten the screw so that the wheels are pressed

more tightly onto the tapered ends of the axle.

As you do this repeatedly check how easily the

back to back gauge moves up and down between

the wheels. At some point, the play between the

wheels and the gauge will be eliminated and the

wheels will just begin to bind on the gauge - this

is when the wheels are correctly gauged. Undo

the operating screw and remove the gauge and

wheelset. Check that the gauge still can slide

betwen the wheels without any play and then roll

the wheelset on a flat surface to confirm that the

wheels run true.

Crankpins

The Exactoscale crankpin range is based on M1 countersunk stainless steel screws, located in an aluminium insert that

fit in a recess moulded in the back of the driving wheel. A shouldered (’top hat’) threaded phosphor bronze bearing is

screwed onto the M1 screw, clamping the moulded wheel centre between the aluminium insert and the ‘top hat’

bearing. The cross-section drawing below shows these components.

To assemble a crankpin, first check the recess in the back of the wheel. It is important that there is nothing preventing

the aluminimum insert fitting correctly in the recess as otherwise it (and the screw head) will not be flush with the

back face of the wheel. It is also important not to deepen the recess as that could prevent the insert and the crankpin

bearing clamping the wheel moulding properly. Then push an aluminium insert into the recess, checking that it is flush

with the back of the wheel (see first drawing below). Take an M1 countersunk screw and check that there are no burrs

at the end of the slot in its head that could prevent it sitting correctly in the countersink. Use a needle file to remove

them if there are any. Push the M1 screw into the aluminium insert (see second drawing below).

Take a threaded crankpin bearing (reduce its length if it is too long for the thickness of the coupling rods being used)

and, holding the bearing surface in a pin chuck, screw it onto the M1 screw. If you are confident that the crankpin will

not need to be removed (or have its position adjusted to get a return crank correctly angled), put a drop of Thread-

locker (Loctite 243) on the screw before finally tightening it to clamp onto the moulded wheel centre. The third

drawing below shows the crankpin in position.

The Exactoscale range of crankpin components includes a threaded bearing extension, spacer washers and two sorts of

crankpin nut (round and hexagonal).

It may be possible to use the round crankpin nut reversed for the recessed nut that is sometimes needed on the

leading coupled wheels of an outside cylinder loco, though considerable thinning of the ‘top hat’ crankpin bearing will

probably be needed to give an acceptable overall crankpin length.

It may also be possible to use the threaded bearing extension to create a robust return crank. Thread a bearing

extension onto an M1 screw (right up to the head). Drill a 1.0mmØ hole in a thick piece of aluminium (or MDF might

do) and place the M1 screw in it - so keeping the bearing extension square to the surface of the aluminium/MDF. Open

out the return crank to 1.5mmØ and place it front face downwards over the bearing extension, then run a bead of

solder round the join between the return crank and bearing extension. Unscrew the M1 screw and screw the return

crank assembly tightly onto the crankpin, check its position and work out the amount of any angular adjustment

needed. Remove the return crank from the crankpin, loosen and retighten the cranpin having made the necessary

adjustment in the position of the screw slot and replace and retighten the return crank. It may take several attempts

but it should be possible using this method to get the return crank tight in the correct position.

As will be obvious, this section does not yet reflect much actual experience of using these components. It will be

extended and updated in due course. Feedback from modellers to help with this will be welcomed.