Quote:
Originally Posted by Gray Adams
That sounds absurdly tight for helical interpolation on anything but the higher class Japanese machines. How are you even measuring that kind of tolerance? Even if you could hold that kind of tolerance, with the thermal expansion of aluminum, holding a part with a 1.250" hole in it in your hand for a few minutes will cause the diameter to grow .00033 in.
Anything even close to that tight should be done with a boring head or reamer anyway.
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We measured on a CMM. Here are the results, listed as nominal, measured
1.1250, 1.1249
1.1245, 1.1250 (our first try, incorrect cutter comp)
0.8750, 0.8747
I did the math for how much temperature affects diameter, and for a 1.125" hole, it was around 20 degrees F to get a change of .0003. It's likely there wasn't a 20 degree change, as the machine's coolant is at room temperature, the part was machined at room temperature, the bearings were installed at room temperature, and the measuring was done at room temperature.