Build a Chassis for a G6

By Rod Shaw

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.



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 chassis spacers!)

  1. 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.
  2. 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, testing regularly until they were right.
  3. 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.
  4. 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.
  5. 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.
  6. 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 them out 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 on 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 fitted - see later.
  7. At this point I painted each chassis side black.
  8. Assemble the motor and gearset as per the Branchlines instructions. I like this gearset as the worm and gear wheel have fixing screws, which seems preferable to press fitting or gluing.
  9. 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, as 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 touching 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 that you can easily take the whole thing apart as often as you like until you're happy with it.
  10. 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 housing touched it, just in front of the vertical grooves in the frames, until the motor sat at a flatter angle.
  11. 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 the 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 be meshing.
  12. 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 end.
  13. 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 off 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 for front 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.
  14. 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. The 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 photo that 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 of the pick-up wire touch the wheel flanges. You can easily adjust the tension to make good contact.
  15. 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 wire to form a good join.
  16. 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 and 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.
  17. 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 need a 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 that they only fit one way because the centre wheels are nearer the front than the back.
  18. 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 from the 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.
  19. 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.
  20. 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. I think they look great - especially on my first chassis!




Photos by Rod Shaw

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Last updated: 08-02-2009