Driving wheels for the C-25.


Being an outside-frame locomotive, the wheels of the Baldwin 10-E type were between the frames. For this reason, the rods and cranks which transmit the motion of the pistons to the wheels can not be directly attached, as they are on the wheels of inside-frame locos. So, the cranks are mounted on the ends of the axles, outside the frames. Without the heavy counterweights and crank bosses we're used to seeing on wheels for inside-frame locos, the wheels are plain, looking rather more like wagon wheels than conventional locomotive wheels. (Sometimes counterweights on outside-frame engines would actually be mounted on the wheels, far out of sight behind the spokes, and on other engines the counterweights were part of the cranks.)

The drawings for these driving wheels were based on standard AAR practice, as found in the 1930 Locomotive Cyclopedia, as well as the G1MRA 1 scale wheel standards. While these standards were developed for 1:32 scale models operating on gauge 1 track, they were somewhat oversized (for reliability of operation), and therefore worked out remarkably close to a finescale profile for 1:20.3 scale on gauge 1 track. And they should work pretty reliably, since there are hundreds or even thousands of locomotives already using the G1MRA wheel profile.


Getting castings done from my drawings was quite a complicated procedure, principally because I didn't really know how to go about doing it when I started. First, I took the CAD drawings to an acquaintance who has a CNC milling machine. He used the front elevation to cut a blank with the basic shape of the spokes, rim and hub from aluminum. Next, a friend with a spin-casting machine cast this blank in a soft whitemetal. This metal could easily be cut with a purpose-made shaping tool, which was formed to the profile of the spokes and used like a spokeshave draw knife is used on wooden spokes.

When the spokes were properly profiled, I took the wheel back to the whitemetal shop, and had a whole set of wheels cast from it. I intended to use these as centers, and had steel tires made for them. The whitemetal was not really hard enough to suit me, however, so I took one of the centers, with a steel tire mounted on it, to a custom jewelry caster. This shop does eleven different kinds of metals, from zinc alloys to silver and gold.

The final castings were made in white bronze, which is much easier to cast and machine than iron or steel, but has the appearance of steel. In the photo are the castings, fresh from the foundry with the sprue stubs still on them. I took a chance and had the flanges cast on them, as opposed to the usual practice of leaving a thick border of material which is later shaped to the size and profile of the tread and flange. I think this will work out fine, because I took my caliper to the foundry when I went to pick them up, and they were, at most, only about .010" out of round. This, I think, will be easy to true up in a couple of minutes on the lathe.

© copyright 1997-9 by: Vance R. Bass .

Updated on 11 March, 1999.