Men,

On the RGS #20 (1900 Schenectady) I saw a photo (by Lynn Modinger) that shows the driver centers and they are not a complete circle, they have about a 1" wide slot gap cut into them in at least one quadrant. This is on at least 4 of the 6 driver centers (the photo shows only 4 of them and its on all 4) . The slot has a filler material in it.

The location is this; if you were on the outside of the locomotive facing the driving wheel, with the pin at TDC, the slot would be on the top left quadrant in the first spoke gap that is located just left of the driver pin.

When I saw this I thought that must be a way to expand the diameter of the driving wheel center to fit a loose tire. Is that guess correct? If so, when was that common practice? I've never seen this before in any book or on any locomotive.

There must not be much diameter that you could make up with this method, but I guess a little goes a long way, considering you can do nothing with a tire thats oversized.

Whats the scoop?

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Thanks Kelley,

So is the spacer there to help the segments to butt up against each other?
Did the segments fit that loosely when new?

That leads to another question, the decorative appearing paint lines radiating out from the axle bore on the 1880-1900 era locomotives must be to show a separation or displacement in the multiple segments of the wheels center, and the extra ones were probably just for extra pizzazz.

I always wondered why they were painted like that, now it might make sense, if that is why they were painted like that.

The "segments" are all one piece, connected at the hub. The purpose of the gaps were to control stress when the cooling casting shrank more along it's circumference than across its diameter. The other common way to handle this on cast wheel-like objects was to cast the spokes in a spiral pattern, as evidenced by cast brake wheels, band saw wheels, and even the gussets on the back of cast iron freight car wheels. The thought was the excess shrinkage would be taken up by gently bending in the curved spokes rather than manifesting itself as cracks in the rim, but this wasn't going to work for spokes in a wheel that was expected to support a significant load.

Obviously, improved foundry practice and materials engineering showed that this wasn't necessary, and later driver centers were cast without the gaps, but the state of the art had not progressed to that point in 1900.

OK, I thought my guess was getting awfully complicated to be practical, but thats the way it appeared.

I've not studied any steam loco designs in depth that were built prior to about 1925 and have never had any real drawings and specs on anything older than 1925. That old stuff is hard to find!

I'm an enigma, and a contradiction; I'm a modern NG fan, I suppose

So are the slot fillers made of cast iron? Whats the fit, maybe a light hammer tap fit?