Chicago Aurora and Elgin car 309 was the first interurban car from that railroad selected for preservation by IRM, and has been running on a regular basis for many years. However, some of the motor bearings are badly worn and need to be replaced. These bearings are large bronze castings and are quite heavy, so this is an expensive proposition. The unfinished castings will cost about $4,000.
Below we see the axle's bearing surface, which was turned down to a smaller diameter by the CA&E. The outer half of the bearing and the axle cap casting have been removed.
However, this project would cost much more except for two things. First, we were able to easily make our own patterns using older, worn bearings, with a plastic pipe glued inside to represent the new material that is needed. Having a pattern of this complexity made from scratch would be expensive.
And secondly, the raw castings need to be carefully machined to perfectly cylindrical surfaces. That could easily double or triple the cost if done by an outside shop, but we have the tools and volunteer expertise to do this at IRM.
So we're asking you, the members, to contribute to the CA&E wood car fund to make this possible. The bearing project should be on the Buck-A-Project page in the next issue of Rail & Wire. Or you can send a donation to the office with the magic words "CA&E Wood Car Fund" or words to that effect. You'll be glad you did. Once we have the new bearings, the 309 will be available for frequent passenger service once again. Thank you!
Randy:
ReplyDeleteUsing an old casting as a pattern can cause problems. First of all, using an old casting as a pattern does not account for the casting shrink rate. Patterns are normally slightly larger than the the resultant raw casting. This is due to the fact that as the bronze cools, it will shrink. The shrink rate differs depending on the alloy that you are using and the shape of the casting. The pattern maker will take this into account when making the pattern. On small parts this is not a big deal but on a large casting like a axial bearing, shrink is a real issue. Also the raw casting needs to have machining stock added so each bearing set can be custom machined to fit each motor/axle combination. It would be nice if IRM had the original bearing casting drawings but I expect that they are LONG GONE at GE.
Randy Anderson
Randy:
ReplyDeleteThanks for your input. We are aware of the shrinkage problem. We know what the percentage should be, and the outer surface of the bearing used as a pattern will have a layer added so that we can machine it to fit the motor frame correctly. The inner diameter of the plastic pipe is 6", which is already too small, so there will be plenty of machining stock that needs to be trimmed down for each axle.
In any case, once we have the money to start the project I would be glad to have as much expert advice as possible. Please come back, I'll buy the drinks!
Randy Hicks
It was always interesting that the Market Street Railway, which had a large foundry, made both halves as one long half round tube with flanges on each end. After the part was cast it was cut in half, the edges were surface ground on a large homemade machine. The two halves were soldered together. The bearing was then fully machined as a complete cylinder. The last step was to melt the solder, resulting in two fully machined halves. They did not custom make bearings. They kept motor hanger bearings in stock at full size, 0.015", 0.030", and 0.060" in diameter undersized. Have you decided what material you are going to make the bearings out of?
ReplyDeleteThank you, that's quite interesting. If I'm understanding your description correctly, the original casting was eventually cut into four pieces, or four halves making two complete bearings. I can only imagine that for streetcars they were dealing with axles a bit smaller than 6 1/2". In any case, the usual method is to solder the two halves together for machining. And I can't tell you off hand what the material is, but the foundry will be matching the original bearings as closely as they can.
ReplyDelete