Machining Locomotive Drive Wheels


The most recent work on my 3-1/2" gauge 4-6-0 was to machine the drive wheels. Here's what I did...

Driver Casting

Start with a casting for a drive wheel. I got the 6 castings from Friend's Models back in the early 1980's. I got 4 "light" drivers, and 2 "heavy" drivers, the heavy drivers being for the main axle. The driver used in the photos is one of the light ones, the heavy drivers have a larger counterweight.

They were designed to be machined to 4" diameter, the size called for in several Friends designs. Since the driver for my engine is 3-15/16, I would have to take off more metal than usual, but that isn't a problem.

Face the Rear

The first step is to put the casting in the lathe and face the back. I did this in my 3-jaw chuck, using a spider to hold the casting off the jaws. I gripped the casting by the tread, not the flange. When you're facing the back, make sure you leave enough thickness for the flange!

Tread and Axle Hole

The next step is to rough machine the tread to thickness, machine the tread diameter, leaving a little oversized, and bore and ream the axle hole. This should all be done in one setup.

When turning the tread and axle hole, you should mount the casting in the lathe and get it running true with the inside of the tread. This is because if the tread isn't an even thickness, the wheel will appear to be wobbling down the track.

This is where life got interesting. I only have one 4-jaw chuck, and its about 8" in diameter. The jaws are big enough that I couldn't grip the flange, since they interfered with each other at the center of the chuck. Turning them around, I found that wouldn't work either as the jaws would have been sticking too far out of the chuck, they would have hit the bed of the lathe.

After some consideration and consultation with my fellow NEMES members, I decided to make a sacrificial faceplate, which I would then mount in the 4-jaw and machine the drivers.

I got a piece of 3/4" thick aluminum plate, drilled a hole in the center, mounted it in an arbor, and turned the outside. This wound up being around 6" in diameter, but that isn't a critical dimension.

I then put a driver on the faceplate, and drilled a series of four holes between the spokes. I also drilled a series of eight holes, two every 90 degrees, on the outer edge. All these holes were tapped for 1/4-28". I made 6 straps out of brass, two holes in each to match the holes in the faceplate.

Having built the face plate, I mounted a driver to the plate using the inner holes, putting the strap across the spokes, and tightened down the bolts. I then indicated in the driver, based on the inner edge, as described above. In this setup, I turned the tread to thickness, machined the tread diameter slightly oversized (.010 or so), and bored and reamed the axle hole.

The photo shows the driver on the faceplate, after the facing operation, but before the tread and axle hole were machined.

Face the Front

With the driver still mounted on the faceplate, use the outer ring of holes to strap down the driver via the tread face. The outer set of holes had a bolt inserted to use as a spacer, the inner hole was used to tighten the strap down against the driver and the spacer bolt. (the picture makes it lot more obvious than the description). At this point, I removed the straps from the spokes.

With the driver secured, I faced the front surface. Debur the axle hole once you're done machining the face.

Rough Finished Driver

After removing the driver from the faceplate, This is what it looks like.

Next Steps...

I still have to finish the tread to diameter, taper the tread to 2 degrees, and machine the flange. This will be done on a tight fitting arbor. After that is done, the hole for the crankpin has to be located and bored/reamed, and then a keyway added to the axle hole. Photos of the rest of the work will be forthcoming...


This page is always under construction!

Last Updated March 27, 2003

All photographs and text © Mike Boucher. Ask permission if you want to use any of it!

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