Cutting flanges question

We're cutting high flanges using the special shoes, carbide inserts and wooden block. Using the specified brake cylinder pressure of about 10 lbs, the piston seems to flex in and out as the loco moves down the track. We are winding up with a legal flange at a given spot on the wheel, but maybe 70 degrees or so around the wheel, the flange is still high. Anybody have an idea what we're doing wrong? One suggestion was we should be using TWO wood block rather than one, but the manufacturer says only one, and they are not familiar with the problem. We don't want to cut too far on the now-legal part in order to bring the high part down, but it probably can't be considered legal until it's all within spec.

Any suggestions? Thanks!

It sounds like your wheel may be out of round and the cutting shoe is following the out of round contour. That would explain the brake cylinder flexing in and out.
LF

Thanks! We considered that but were not totally convinced that was the problem. But we might have found the answer, or part of it anyway. The truck in question is a switcher truck, and has a dual cylinder. So there is a whole 'nother piston, and any time the one we're cutting with has an increase in pressure from one cause or another, there is a wave effect involving the other piston, In time this can become self-reinforcing. I might add we had the other slack adjuster backed off to avoid brake shoe drag while towing the loco being worked on, so there was virtually no resistance there.

Does this sound reasonable? We're going to get a new wood block for the cutting shoe, snug up the other slack adjuster, and see if that makes a difference. Or does anybody have other suggestions?

Is there any way that you can block the cutting shoe so that it only hits the high spots? If you look at this like truing up a piece of round stock in a lathe, your first light cut usually hits just the high spots. That is because your cutter is in a toolpost, and at a fixed location from the work.

In the case of a cutting shoe, if the wheel is out of round, the cylinder allows the shoe to follow the contour. I suspect that the flanges will come to the proper contour eventually, but at the expense of a lot of good meat, and the wheel will still be out or round.

Disclaimer- I've never used a cutting shoe myself (I have run locomotives back and forth with them on-) but I have used a lathe (in a machine shop, not a wheel lathe) quite a few times.

Thanks to those who responded both on and off the forum. Today we tackled another wheel and with the changes above it worked fine. The mistake was in backing way off the slack adjuster on the other wheel on the same side of the truck. Our thought had been to lessen drag and wear as we cut the wheel in question but forgot that since the switcher truck has two pistons fed from the same cylinder, we were defeating ourselves by allowing so much slop.

Today's work, leaving the other slack adjuster as it was, went fine with no distortion or pulsing of the piston. Today's wheel is fine. Since the wheel treads themselves are OK, we will experiment with using TWO blocks of wood, perhaps a bit oversized, in an effort to trim the high spots only on the wheels with the problem. If that does not work out, a fixed lathe may be the answer.

Again thanks for the help. Hopefully someone who has not yet tackled this job will remember our lesson and not make the same mistake.

i've seen grinding shoes, but the ones i have seen have no carbide cutters in them, just abrasive [like a grinding wheel]... we machine our wheels if the flange gets bad... we've got 2 stanray [sp?] wheel milling/truing machines...