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Originally Posted by sanddrag
What I am saying is that the inherent tolerance in that machine is more than 5 times that large (at least probably .0004 as opposed to two microns which is ~0.00008). If you are making parts with a tolerance of 2 microns, you won't get it on that machine, which is why I have no idea how anyone familiar with common machining would even bring up anything about 2 microns being a problem (requiring the installation of a backup battery).
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I know for a fact that the type of tolerances you're quoting are indeed valid for a VMC in a production-line setting (e.g. 200 pieces/day, loaded by a robot, high-speed material removal, shop floor environment, etc.). However, with the proper measuring apparatus, and the proper machine, and the proper tooling, and the right conditions, significantly better tolerances can be achieved (as in, an order of magnitude, or better). Diamond tooling and laser interferometry, in combination with a
very stable machine can produce complex compound surfaces with tolerances of several microns (of which two microns might be a significant enough portion to worry about, if it would cause a higher proportion of rejects).
I'm not saying that this machine can necessarily do this, because I haven't consulted the manufacturer or the previous user for its specifications; I am saying that there exist similar machines which can, and that minus the fantastically expensive custom tooling, fixtures and metrology equipment (e.g. laser interferometer, etc.), it's conceivable that a small, used one like this could be worth $100 000 (USD). (And I say small, because the ways don't have much travel, the workpiece size is rather limited, and it fits in about the same space as a regular manual knee mill. To clarify further, I was being slightly facetious when I called this "just right for a FIRST team"; it's overkill, I know. If only there was a :facetious: smiley....)
Now, if Matt is correct, we might as well forget this side issue....