Following a discussion at the St Albans show I commissioned a 3mm scale version of their new loco building jig. It is made from laser cut plywood and comes complete with 1/8″ axles turned down at the ends to take coupling rods.
I am now trying it out to build a chassis for a 0-4-2 GWR 517 class tank. This is the 3 mm society kit reduced down from Malcolm Mitchell’s 4/7 mm kit.
The instructions suggest using the supplied silicon tube to hold the chassis central in the box but I was worried about keeping it square. The first axle is inserted in a central hole and the second is fitted through a slot and the wheelbase is held by using the coupling rods. I have threaded top hat bearings with the flange towards the centre of the box onto the rod first. When the side frames complete with bearings are threaded on they can be pushed tight up to the other bearings and this keeps it all square.
I am building the chassis to 14.2 mm gauge but not compensated as there isn’t enough room to get rhe beam around the gearbox. If building a chassis with hornblocks this will be ideal to get them in the correct position before soldering up.
The chassis spacers can be tack soldered to one of the side frames and then the whole lot is set up in the jig before finally soldering up the spacers.
Overall I think that ,compared with other more complicated and expensive jigs ,at £25 this is good value. My only worry is that the central, fixed axle hole will wear in time. I may fit brass bearings to this hole to stop the wood wearing.