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Re: tapping CIM axles?
I was interested in how well the shrink-fit was able to transmit torque from the shaft to the hub, so I made a quick calculator to evaluate a sample design.
An aluminum hub with arbitrary length, shrunk over the 8 mm steel CIM output shaft, is able to transmit a maximum of 4.2 N*m for every 1 mm of hub length (or 78 ft*lbf every inch). It requires a total radial interference of .009 mm (or .0004 in). Assuming linear thermal expansion, it takes about 190 F of heating to achieve this radial displacement.
Greater amounts of shrinkage can be achieved, but they'll force you to cut into the safety factor you're using for the maximum circumferential stress in the hub.
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