The prototype J15 had 15 spoke 4'11" wheels. Unfortunately the nearest available from Alan Gibson in a 4'11" 16 spoke wheel or a 4'7" 15 spoke. Gibson sells a pack of the 4'11" 16 spoke wheels with 2mm axles as a conversion set for the Hornby J15 (which has 2mm axles) and on reflection the 4'7" really does look noticeably too small to me. The Brassmasters' sprung hornblocks come available as 1/8" or 3mm bore so my decision to use the conversion pack wheels meant I also had to use Gibson's 1/8 to 2mm bushes (part # 4M68). These soldered into the Brassmasters' hornblocks without difficulty and were a good tight fit.
The Gibson wheels were of the design which doesn't have the crankpin hole fully molded/drilled - you just get a small dimple. The chassis will only run smoothly if all the crankpins are vertical to the wheels and the same distance from the centre of the axle. This is something which is pretty hard to achieve with just a drill in a pin vice and not much easier with a pillar drill unless you make some kind of jig. The jig just consists of a stub to mount the wheel on, this needs to be sliding fit so slightly smaller than the final axle size and an arm which has a hole through which the crankpin hole can be drilled. Using a bit of square tube means that the drill has two points held in place and will therefore drill at the same angle each time.
Not very original or pretty, but functional. The shim on the right supports the wheel on its flange rather than it being supported on the plastic boss.
Having made the jig I got 6 wheels fitted with crankpins. They may not be perfect, but if they are all equally imperfect things should at least run!
I managed to get the wheels, bearing, extra washes to reduce sideplay and the original Hornby drive gear into the GW wheel quartering press and squeezed together. This is always a job I loath and it seems to always have a high 'F' factor but to my amazement I ended up with only slightly wobbly wheels. I've got to say that this is one of my least favourite jobs in locomotive construction!
The coupling rods assembled together nicely with the joint being made using little rivets from Markits. The final rod pivoted easily but had no play in the joint. With the wheels in the chassis the crankpin holes in the rods were opened up with a broach to be just a fit for the Gibson crankpin bushes and amazingly the rods slid onto the crankpins and aligned well. One of the advantages of this type of chassis design is that you can assemble the whole unit as a rolling chassis and check for binds before fitting back over the original chassis block.
I'm afraid I lost count of the number of crankpin nuts I Iost on the floor!
The unit fitted nicely over the chassis block and because the Hornby tender can work temporarily with just a set of P4 wheels dropped in I was able to provide pickup to the motor via the tender to test the chassis.
There are a few corrections to be made to the etch, at the moment the frames foul the footplate at one end so the body won't fit on quite correctly but getting something to move under its own power is always good for the motivation.
There is a little clip on Youtube at https://youtu.be/QbPApw3bIyQ