Was that 10 F difference for the 68 to 78 degree difference?
It seems to me that you would have to account for expansion differences only
if the machining was done at a temperature different than that for the
*intended use of the part*.
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"BottleBob" wrote in message
...
Anthony wrote:
Keep in mind that the "standard" temperature for measurements is 68°F.
Course, if your tightest tolerance is +/-0.02" then the temp won't matter
too much if you run to the center of tolerance. If you do any tight
tolerance work though, you'll need to do a temperature correllation and
adjustment based on the actual shop temperature and material being used.
Anthony:
I was doing some 132" long aluminum aircraft seat mounting rails for
Boeing about 10 years ago. Our shop air conditioning temp. is normally
set to 78 degrees. The parts had lots of holes (whose location was + or
- .005 from one end), and other misc. features. They were done in a
Fadal with 40" X travel with both end door removed, and they were
advanced by putting one of the prior drilled & endmill bored holes on a
fixture pin. Any length errors would probably accumulate.
The bottom line was that I looked in Machinery's Handbook for the
coefficient of linear expansion for 6061 and adjusted my geometry and
toolpaths by the amount for 10 degrees difference. (I remember it being
something like 1/2 a thou for every 4 or 5 inches or something - I could
be off though it's pretty fuzzy after all this time). I did a test
piece and sent it to be checked with the subcontractor's CMM, and it
came back OK, so we did the whole run. We warmed the machine up and ran
the coolant till it was close to the 78 degree shop temp. before running
parts.
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