wheel runout in steam locomotives

[Anonymous]

mountains out of molehills. my lack of experience shows. I guess reading books always helps, but can only augment practical experience. Maybe someday when I'm growed up.........

[dldance]

For all of its mass, the drive wheel system of a large steam locomotive is surprisingly flexible. Each axle is separately sprung and equalized. The bushings ands rods have to allow this motion. Just think of a set of driving wheels crossing the gap in a diamond. The drive wheel may have a verticle movement of more than 1/4 inch - which will change the pin to pin distance on adjacent wheels by several thousanths, etc.

dd

[Anonymous]

I posted this in the morning and after having a day to think am now replying in the evening, and I realize that if I had thought a little further I could probably have answered some of these questions myself.

I understand that a tire's position on a wheel could compensate for lateral or axial variation in a wheel, I was more concerned about how dimentional changes within the diameter of the wheel could affect a driving pin's location, but I guess the pin's bore in the wheel could always be bushed or rebushed and then machined to correctly position the driving pin.

I also understand how center to center distance between drivers can be maintained and an axel's squareness to the frame.

What prompted my questions was that even after machining a new bushing for the connecting rod, the problem was not completely solved, which made me wonder that if the problem was not in the bushing or the pin itself, could it be in the wheel?

I guess though that unless I was actually there to inspect the pieces and rule out other possibilities ( too tight a fit? a distorted pin? axel play or out of square? out of quarter?) this is all speculation, and something like out of quarter could be dificult to determine out on the road.

I guess the question struck me as something I haven't thought of before.

[ndbprr]

The steam engine was a pretty simple machine capable of handling differences in allignment pretty easily. The bearings urfaces were all brass on steel and were adjusted almost continuously for wear and allignment. Tires when installed were pretty soft because they were heated to expand them and then shrunk to the wheel. An engineer had to be very careful for a couple hours of running so he didn't lock them up and flat spot them. I'd bet every wheel ever turned had some out of roundness to it but the rigging and springs could compensate. We probably aren't talking of a problem with anything under sixty to one hundred thousandths any way.

[dldance]

I amy be wrong here - but I was always under the impression that wheel runout could generally be corrected by truing the tires on a wheel lathe. The tire is a machined steel rim that includes the flange and tread and is a separate piece from the cast center of the wheel. Similar to the iron tire on a wooden wagon wheel.

dd

[Anonymous]

I just read the article by William H. Johnson and got to wondering if excessive runnout in a driving wheel of a steam locomotive could significantly affect driving pin alignment.

Is it possible for the forces transmitted to a driving wheel by connecting rods enough to cause a wheel to warp over time?

I imagine even a small change in a driving pins angle in relation to a connecting rod would cause an increase in thrust forces by the connecting rod either against the wheel or the nut flange depending on the piston's direction.

What amount of runnout is considered excessive? Is it common, or rare to experience a problem caused by excessive runnout?

Was this a reason for disc drivers in later years of steam locomotive developement?

I have read of rod bushings with a spherical O.D. to allow for missalignment and movement between drivers. Is this a design feature of all steam locomotives or an exception?

I imagine straightening a wheel would be pretty difficult, possibly by carefully heating and cooling parts of the wheel in appropriate places to "unwind" it.

Could wheel runnout significantly affect the dynamics of the locomotive as a whole?

Could excessive heat or heat cycles from regular operation over time cause excessive runnout?

I don't know what kind of answers this will prompt, but I hope the questions are at least interesting and thought provoking.