I started with a set of frames which had already been made. I was going to say - which saved a lot of sawing - but in fact I would probably have cut them in the mill.
The important thing is that the two blanks are riveted together and treat as a pair until complete.
As I had no idea how mine had been done, I started with dimensional checks. I soon found that the axle box spacing was marginally different (of the order of 20 thou) from one side to the other. And the horn slots had been finished individually and were different (hence the axle box spacing). Apart from that, they seemed ok.
I set the frames on parallels standing on a surface table.
The structure was not truly parallel, with a rock of at least 1/16 in in one corner. I slackened fixings and kept rechecking, until I found that the central cross braces were the cause of the problem - one was a few thou out of parallel. I milled a few thou off to make it truly parallel, and made up a shim (only 5 thou) to keep the spacing correct. I doubt if it was worth it - but at least its accurate. I kept rechecking as I re tightened fixings, and eventually it was dome.
The next thing was to put in the axleboxes and check the axle centres. For the completed wheel sets, there was only one way to fit them because of the differences in hornblock and axlebox dimensions. I actually checked these by mounting the wheel sets between centres on the lathe, and measuring the offsets from the axle to the hornblock slots.
Again, all were different. I guess that the frames had been set up as a pair, with the blank axleboxes fitted, and then the axlebox bearings had been drilled and reamed in situ. So the wheel centres do end up the same on both sides of the frame.
If I was starting from scratch, I'd have done it differently. Like, I'd have kept the frames as a pair until after the hornblocks ha been milled.
For the axleboxes, I's have squared up the axlebox material, and drilled and reamed - or bored - the axle bearing. Then I'd set it up in the mill, with a stub axle through the journal, and resting on the jaws of the milling vice, and the upper surface horizontal. Then I'd have milled one of the recessed for the horn block.
Having done that and set a stop on the milling machine quill, I'd have rotated the axlebox through 180 degrees,(a small parallel and a couple of jackscrews will do the job) and milled the other horn block bearing. That way, they all end up identical, and with the axles central.
Comments