Making a Chassis for a G6
An Inauspicious Start
My introduction to chassis building was not a happy one, being an abortive
attempt to build a tiny LNER Y7. No reflection on Messrs Finney and Smith,
from whom I bought the kit - it's just not a beginner's project, and after
two dismantlings I still haven't got it to run well or to fit inside the
body. One day I will succeed, but for now something more straighforward was
needed, so I decided to have a go at the SR G6 0-6-0T from 3SMR.
Apart from oddments I sourced all the
parts I needed from 3SMR and Branchlines.
- Etched nickel silver chassis from G6 0-6-0T whitemetal kit - 3SMR Cat. No. C8/X.
- Romford 14" diameter wheels - 3 live, 3 insulated, middle wheel
on each side unflanged to cope with my tight curves though this is obviously
a matter of choice. 3SMR Cat. Nos R/18 (x2), R/18U (x1), R/25 (x2), R/25U
- Romford axles with wheel nuts - 3SMR Cat. No. RA.1 (x3).
- Romford crankpins with washers - 3SMR. Cat. No. R31/6 (pack).
- 2 Romford 0.005in. brass washers - 3SMR Cat. No. R.62 (pack).
- 6 Romford axle nut covers - 3SMR Cat. No. RC.2 (pack).
- 1/8in. straw-hat bearings - 3SMR Cat. No. L/065 (pack).
- 1 cast spacer - 3SMR Cat. No. L/093 (pack of 2).
- 2 Branchlines screw-up frame spacers (pack of 3).
- Mashima 9/16 motor and RSL 50:1 gearbox from Branchlines.
- Piece of PCB approx. 5mm square and 60mm length of pick-up wire.
- 2 small lengths of fine plastic-coated wire, 20-25mm long, for motor
- Small brass strip, approx. 6mm by 12mm, bent at right angles for mounting
pick-up on chassis.
- 2 more brass strips, approx. 5mm by 10mm, for fixing motor to chassis.
- 145 degree solder and 12% phosphoric acid flux, many sources, bought
mine both from London Road Models.
- Soldering iron - mine is a 12W Weller which I've had for ages. This works
fine, though I believe 25W or thereabouts are generally recommended.
- Romford nut driver - 3SMR Cat. No. R.11.
- Set of precision screwdrivers.
- Flat and half-round needle files.
- Small wire snips or craft knife.
- Araldite Rapid or superglue (I used the former).
If a picture paints a thousand words, look at the photos and theoretically
these instructions won't be necessary, but here goes anyway. (You may think
from the underside view that the chassis is skewed, I can assure you that this
is an optical illusion caused by the irregular way I cut the front and rear
- The only chassis parts supplied with the kit are the frames and coupling
rods. The latter come attached to the former and need separating with snips
or craft knife, then the edges of the four components need smoothing with
a flat needle file where they were joined together. Try to file along the
length of the component rather than cross-wise.
- The most significant modification is to enlarge the axle holes to take
the bearings. I did this by rotating a half-round needle file inside the
holes. A round file or taper broach would probably have been better but
I used what
I had. The final diameter of the holes had to be a bit bigger than the
file's width, so I carefully carried on filing in a sort of circular action,
regularly until they were right.
- Solder in the strawhat bearings by putting each one in place then running
flux and solder round the rim. Take care to get them in the right way round.
- Solder one of the terminal wires to the right-hand inner side of the
chassis, between the centre and rear axle holes, pointing upwards so as
to be able to connect the other end to a motor terminal later on.
- Solder a piece of brass bent at right angles inside the left-hand chassis
side, again between the centre and rear axle holes, so as to be able to
take a piece of PCB on its underside. This has to be far enough back so
as not to obstruct the gear wheel later (mine was a close shave), but far enough
forward not to get in the way of the rear spacer.
- Fit the chassis sides together by screwing in two of the Branchlines
spacers. There are small holes provided for this, but you may have to open
slightly with a needle file or broach. Even with screw-in spacers, there
is scope for getting the sides slightly misaligned, so I held them upright
a sheet of glass while tightening. The screw heads stand slightly proud
of the chassis sides, this caused a shorting problem when the wheels were
- see later.
- At this point I painted each chassis side black.
- Assemble the motor and gearset as per the Branchlines instructions. I
like this gearset as the worm and gear wheel have fixing screws, which
to press fitting or gluing.
- Screw an insulated wheel to one end of each axle. The insulated wheels
are the ones with a thin brownish fibrous rim in between the tyre and the
spokes - if you are not used to Romford wheels, you will need to look carefully,
I had to, to spot them. I then fitted one of the 0.005in. spacer washers
to the axle of each insulated flanged wheel - so as to avoid the wheels
the spacer screws and causing a short. I found this out by trial end error
after the motor was fitted and wired but might as well mention it now.
One of the beauties of screw-in chassis spacers and screw-on wheels is
can easily take the whole thing apart as often as you like until you're
happy with it.
- Another thing I found a bit later on was that the motor was angled rather
high, and I thought this might foul the top of the body later, so I filed
down the top of each chassis side at the point where the front of the motor
touched it, just in front of the vertical grooves in the frames, until
the motor sat at a flatter angle.
- Push the axles through the chassis bearings with the insulated wheels
on the left, not forgetting, in the case of the centre axle, to position
the gearbox axle hole and gear wheel so the axle passes through them. Keep
screw of the gear wheel to the right hand side to stop it fouling the contact
wire later. Tighten the gear wheel screw. The worm and gear wheel should
- Screw the right-hand (live) wheels to the other ends of the axles, not
forgetting to quarter, then make all axle nuts reasonably tight with the
Romford nut driver. I didn't bother making them fully tight until the very
- I lied when I said that only frames and rods are supplied with the kit.
It also comes with brass frame spacers. Discard these, they are too wide
to use in conjunction with the Branchlines ones. Instead, I used bits cut
one of the 3SMR cast spacers which I had bought just to see what they were
like - these are about 30mm long and I couldn’t see how to fit one
in its entirety, but cutting a couple of chunks off gave me a piece each
and rear, which I araldited in place, for strength and possibly for fixing
to the body (which I haven't made yet). You could probably use Society
brass spacers, but I don't know what these are like.
- Now for the tricky bit - electrification. For pick-up wire I used one
strand of wire from an old bicycle brake cable. This is tough, and I have
also used it successfully to make a very unobtrusive Tri-ang style uncoupler.
only problem is that it is somewhat twisted and I straightened it to an
extent by dragging pliers along it a few times. But you'll see from the
it's still rather curly. Of course, you could always use 'proper' pick-up
wire instead and I expect you will!
Bend this wire at each end to make contact with the wheel flanges and loop
the ends. Solder it to the PCB, along with the other motor contact wire.
Glue the PCB to the underside of the brass bracket, making sure the ends
pick-up wire touch the wheel flanges. You can easily adjust the tension
to make good contact.
- Attach each motor wire to a motor terminal, I simply bent the end of
each wire round a terminal with pliers, then bent each terminal round the
form a good join.
- Now for testing on a piece of track - the centre wheels should rotate.
If they move the wrong way, swap the terminal wires round at the motor.
If they don't move at all, check the wipers and motor wires for good contact
make sure none of the metal components is shorting, e.g. that the wiper
is not touching the gear wheel. Persevere - if I can do it, you can.
- If you want to fit axle nut covers, make sure the nuts are good and tight
and fit them now. I forgot, but then realised I might want to take the
wheels off at some stage anyway. Screw in the crankpins, you will probably
small pair of pliers to get a good grip. Then fit the coupling rods, I
had to open out the holes a bit by twisting the needle file in them. Note
they only fit one way because the centre wheels are nearer the front than
- Test the chassis again. I hit two problems which stopped the wheels from
turning smoothly. Firstly, the motor moved up and down, pivoting on the
axle, because I'd forgotten to fix it firmly. This made the worm disengage
gear wheel. I cured it by gluing the motor to the chassis sides with two
small strips of brass, one of these can be seen below the armature. The
top 1mm or
so is bent over to grip the magnet. If I'd thought about this I might have
come up with a better way of fixing the motor, round about stage 10.
The second problem was that the holes in the coupling rods needed enlarging
very slightly for the wheels to move freely. I gather that if you open
them out too much, you get the same problem so be careful.
Even then the chassis kept stopping at intervals. I knew the track was
clean, but I realised that at certain points, one or other of the rails
had a slight
upwards or downwards kink in it which made one or more of the wheels lose
contact. I suppose that's where compensation comes in, maybe next time.
- Finally cut the crankpins to size with snips, file the ends smooth and
glue on the washers, taking care not to stick them to the coupling rods.
Then lubricate the worm, gear and axles and run in.
Well, I think that's everything. I'm pleased (and relieved) to have got
it working, and I'm sure you can too. Some say Romford wheels look heavy.
they look great - especially on my first chassis!
Photos by Rod Shaw
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Last updated: 08-02-2009