Plan for quartering jig

While I have the excellent GW Models wheel press and used it on #10, it has two failings from my point of view. First, it assumes a press fit for the wheels; that’s one thing with a plastic centre, but another for steel centres and axles where the two parts need to be machined to within about a thousandth of an inch, and even then they are not assured to stay aligned. The second failing is that the press relies only on the surface of the wheel boss to hold the wheel perpendicular to the axle; indeed, all presses seem to suffer from this failing.

I wish I could remember where I got the idea for this jig. I think it is a combination of ideas from articles in Model Railway Journal and a web article I found while looking for sources for split axles. If you recognize the idea, please post a comment so I can recognize the giants on whose shoulders I stand.

The essential idea is to use a wheel permanently affixed to an extended axle, and to hold the two ends of the extended axle in alignment to ensure that the wheels are perfectly parallel. The extended axle is much longer than the wheel is thick, and twice as long as the wheel’s diameter, making it not only excellent for wrapping the chuck of the drill press, but also for aligning the wheels. So, holding the axle within a reasonably tight tolerance, the wheels should come out parallel. To ensure that the jig repeats quartering to a high degree of precision, it is much longer than the crank-pin throw.

I’ve made the plans for the jig available with a Creative Commons license on OnShape. I haven’t parameterized the design yet: you just get my dimensions, but it would be easy to modify so you plug in the wheel widths, crank-pin offset and gauge, and have OnShape produce a drawing for all the parts. If you plan to use the design, let me know and I’ll parameterize it for you.

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