Quote:
Originally Posted by InFlight
There seems to be an assumption that a basic lathe comes from the factory, and continuously maintains perfect alignment between the tail stock ram axis and the spindle axis; to allow perfectly on-center holes to be drilled.
The reality is it takes a somewhat experienced machinist with a test bar and a dial indicator to adjust the tail stock to be aligned perfectly laterally and vertically. The average FRC lathe is use is likely only accurate to 0.01 inch on-center.
Drilling center holes to the stated -0.0000/+0.0006 on center tolerance would be a non-trivial challenge for many FRC teams. To do it consistently you would need to use a collet holder in the spindle.
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You're confusing the shaft diameter tolerance with TIR. The H1 encoder has a maximum TIR of 0.006", and the shaft itself is between 2 and 6 tenths undersize (-0.0002 to -0.0006).
So the shaft diameter has a tight tolerance, but the encoder might have up to 6 thou of runout, an order of a magnitude larger than the shaft diameter tolerance.
In any case - using a reamer would give you a nice clearance fit, and then use a set screw/retaining compound/whatever to hold.
If your lathe is poorly setup, and doesn't drill holes on center:
1) Fix that
2) It doesn't matter - since the 1/32" piece of lexan holding the encoder will happily flex/float if the encoder has any axial/parallel misalignment. Same idea as using a helical beam coupler/flexible coupling that can deal with axial/parallel/radial misalignment.