On Geoff Stenner said
I have used these gearboxes on split axles. Sometimes it is a question of getting the split in the right place, but another option is to turn, or get turned for you a tufnol axle bearing to replace one of those in brass. The whole assembly remains live to one side of the frames, but will not bridge to the other if care is taken with further insulation inside the loco body.
Which is a good point to illustrate exactly this…
Building split-chassis frames, I’m acutely aware of the risks of shorts. To do this, I take two steps once the body is finished, bar the final details. I line the underneath of the running plate and any other areas that could possibly touch either side of the split chassis frames, spacers, etc.
Because I build fully sprung chassis – Continuous Springy Beams, to be precise – I also line the sides of the gearbox. This is in case any slight vertical, cant or lateral movement brings it into contact with something that it shouldn’t:
In both photos, the insulating material is cigarette papers – I use green Rizla, bought from the newsagent every so often. I get through quite a of them for a non-smoker, as they are useful for temporary washers, and the like.
I fix these using a very runny Zap superglue, so that it soaks through the paper, and it can adhere as closely as possible to the underlying surface. And of course it takes paint very well, should that be needed.
The total thickness of the paper+glue is the smallest fraction of a millimetre, so there is no risk of your buffers suddenly ending up a scale three inches too high. In the pictures, the papers have yet to be trimmed back. With the glue thoroughly dry, it can be easily trimmed with a sharp scalpel, like five thou plasticard, but much, much thinner.
I hope that this inspires people to give split-chassis a try. It’s really not difficult, if I can manage it very successfully.