I honestly don't think that the thermal expansion of the machine is all there is to blame. I have messured a half thou of movement in a h13 tool steel blank I made for a mold maker a couple of years ago. I machined it in the afternoon at about 87deg F. and when he decided to check the part is was about 43 deg. in the early morning. I had to convince him to check them in the afternoon (after all the machine is hot as hell when in operation). I don't think the material should have grown so much but it was customer supplied so there was nothing to say there (fortunatly).
So with that said I think the coolant heat transfer to the part is a big cause and coolant looses its heat alot faster than the machine.
just a thought and since I haven't done any in depth study (being since I rarley do that close tol. stuff anymore) I have no way to verify my theory. :P
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thanks
Michael T.
"If you don't stand for something, chances are, you'll fall for anything!" |