Belleville washers are precision pieces, so I'd imagine the tolerances would be pretty tight. Do you think the hole is deformed, or is it the shape of the "cone" that is the problem?
Not without knowing the application ! Or do you mean "what are the manufacturer's tolerances" ? If that is the case, it would depend on the manufacturer - one of the best is Schnorr (German) - I always specify those, and I am sure you would be able to get the angular tolerances from them. It must be a very unusual or critical application for this to matter very much.
The application is a tie rod on a belt feeder, and the act of compressing the spring stack results in a small angular displacement of the tie rod. Angular alignment tolerances do not seem to be discussed in the Schnorr handbook.
They may not be in the handbeek but I'll bet that someone at Schnorr can tell you what they are. You may need to be able to speak German though. I'm skeptical that you will be able to do any better than Schnorr - so it is probable that you will eventually have to resolve this from a design perspective.
On reflection, the other thing that puzzles me about this is that,if you have a lot of springs in the stack, you would think that the inevitable random angular orientation would normally eliminate any major bias. What is the fit of the springs on the guide rod (assuming you have one) ? You need a close fit , otherwise stacking errors can produce the effect you are experiencing. There is another German disc spring made by Mubea, which has a special bore profile, such that you can have a closer fitting rod. I think at one time they were being imported by Advanced in Rockford.
