The Arnold-Minitrix Shay

Part 1 of 3: Mechanism

Back in the I desperately wanted a Shay for my little logging railroad. So... I built my own. Not having a machine shop—let alone the skills to use one back then—I had to make do with what I could assemble from the comparatively limited assortment of merchandise available in those days, using only simple hand tools. Given that, today, one can purchase an exquisite, accurate N scale Shay from Atlas for a very reasonable price, it probably isn't worth the effort to attempt what I had done thirty years ago. Yet my clunky old Number 6 still seems to generate interest, so here's what it took to make it.

One of my goals was to model something a little unusual. It seemed too obvious to fashion a hulking "modern" Shay from an ordinary diesel chassis; I wanted something much smaller and older, like a partially-homegrown, third-hand, patched-together two-cylinder job from the turn of the century that one might stumble upon on some forgotten little backwoods railroad in the middle of nowhere. At the same time, it had to be based on a robust, reliable mechanism. Back in the day, Minitrix was the industry leader, with a line of exceptionally well-built locomotives, so a decent mechanism was at hand.

I started with the guts of a Minitrix Fairbanks-Morse H-10 switcher (above), the selling points being its compact length and versatile mechanism parts. The first stage of modification was to chop away nearly half of the frame. After firmly clamping the frame in a vice, I cut away the excess material with a hacksaw.

Cutting had to be done with the utmost care in order to avoid placing any strain on the remaining slender parts along the bottom of the frame, some of which had a profile measuring only fractions of an inch. All of the cuts were smoothed with a flat file, burrs and hard edges were removed with a steel wire brush, and then the frame was thoroughly cleaned to remove all traces of metal residue.

Instead of the original FM trucks, I used a pair from a friend's dead Minitrix U28C to take advantage of their slightly closer wheel spacing. In reality, the minuscule difference between them (shown at right) almost wasn't worth the effort, but given that any typical diesel truck was enormous compared to a Shay's, I was eager to save every possible scale inch I could.

After lopping off the dummy third axle sections of the truck frames, I tapped the small existing holes in the underside for 1-72 "junk box" screws that would hold the trucks together, since the portion that was removed also served as an assembly point. The wheel wipers, insulators and side-frames all had to be modified to work with two axles instead of three, and the small hole, conveniently located on the bottom center of the truck frame, was tapped for the new 1-72 assembly screw. Finally, the Rapido couplers were replaced with Micro-Trains. In the photo below, the truck parts on the left are the originals; on the right are the modified parts.

Since the center of the frame was narrowed, the fuel tank, which held the electrical pickup plate in place, had to be discarded, and so I had to devise some new way to secure the pickup plate. Unable to come up with something clever, I resorted to permanently attaching it with CA. Ordinarily I try to avoid such methods, but after careful consideration, I could not see any obvious disadvantage to it (if need be, it could be removed by heating it with a soldering iron). The insulator and pickup plate were modified as shown at right, with unmodified parts on their left. The wire, which originally powered the headlight, was instead connected to the motor.

With all of the major modifications done, the mechanism was ready for reassembly. One (literal) twist I did was flip the motor end for end and also rotate it on its side. My motive for doing this was to keep the boiler as low as possible; however, this meant having to make a large, unsightly rectangular enclosure behind the cylinders for the armature. In retrospect, I might have been better off leaving the motor oriented vertically and just raising a short section of the boiler under the steam dome—the cab would still have fit. But thirty years after the fact, hindsight can be mighty sharp.

Continue to Part 2
Return to Chapter 3
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