X3 mill with rails, ATC, new motor

[Jonathan]

loved the bolt spacing theory so thanks for sharing that, cant wait to see the rest, keep up the good work !

Since you seem to like bolts, here's my justification for putting four setscrews in the motor pulley...

A setscrew works by applying a force which results in a contact force between the opposite side of the shaft and bore. Based on the tightening torque of the setscrew, we can calculate this force and if the co-efficient of friction between the shaft and bore is known, the holding torque can be determined - approximately of course.

For one screw it's very simple - the axial force on the screw is equal to the contact force (C) between the shaft and bore, so:

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The motor shaft diameter is 12mm, we can fit M5 grubscrews, they're black and according to this list the tightening torque is about 4.7Nm, so substitute that lot in:

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With multiple screws, we have to resolve the forces to find the effective contact force. Define the angle as the angle between the two screws, then resolve the force on one screw in the radial direction and double it to get the radial force for both screws:

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I put the screws spaced at 90° because it makes milling the flats on the shaft easier, but this formula shows that the smaller the angle between the screws, the greater the holding torque, so 60° would have been better. For 90° that reduces to ., so now we have .. That torque is a little greater than the motor rating, but shock loads could impose much higher torques so I added another two screws further along the shaft to double the load capacity.

Some pictures I forgot to post of testing the motor: