In my previous blog on this subject I mentioned I'd 3D printed some wheel centres to fit into Alan Gibson 4'10" tyres. I put these into my test chassis and got it working but I was not entirely happy with the result. The issue I believe is that 'Gibson Style' wheels rely on having the centre molded out of a fairly 'grippy' plastic, the hole through the centre is designed to be a good tight fit on an 1/8th inch axle. even so most of us have had a wheel be a bit loose at times and some people resort to pinning the wheels to the axles. Those modelling in OO and EM have the opportunity to use wheels from Romford, now Markits which make use of an axle with a square end which fits into a square hole in the back of the wheel.

I thought I'd try and replicate this with my wheel centre print so modified the wheel centre to match the style of a Romford wheel and I purchased some Markits EM axles. Obviously the P4 Back-to-Back is slightly wider than the EM one so my wheels needed a little section in the back to take their thickness out so that when fastened to the EM axles they present a P4 Back-to-Back. The drawing shows the rear of the wheel centre.

Printing horizontally does mean that the back of the wheel has all the support structure which needs to be removed but it cleans up alright (photo taken half way through the process). The key is not to interfere with the central boss and just to make the rest of the wheel rear smooth. I've put a touch of black sharpie on the rear of the wheel to better show up the square whole. I had to play about a bit with the model to get the right size central boss.

A little bit of trial and error was needed at this point but in the end I fitted all 3 axles to the test chassis and the quartering of the wheels worked from the get-go. Obviously I'll need to make some covers for the axle ends but the result took less effort than using my GW wheel press.

I have now assembled the footplate and cab sides and it all fits together quite nicely with the 3D printed boiler though nothing is fastened down at this point.

I've borrowed a GW models roller to roll the cab roof (thanks Middlepeak) so that is the next job on the cab. Although I have etched the brake gear I've also produced a 3D printed version of the brake hangers and brake blocks to see how they work and whether they are robust enough.

I also need to make up the tender chassis, I've rubbed down the tender sides very slightly to remove a little bit of marking from the printing process.

All together I think it is some good progress.

David