King Midas mill conversion

[Robin Hewitt]

What's the dimension I've marked with '???':

I'm confusing my milling machines, on this one I used full nuts rather than pairs of half nuts. I didn't want to stress a half nut by asking it for 500 lbf of tension.

10mm for the bearing, 10mm for the nut, say 1mm protruding, 21mm total.

Doesn't really matter how far the thread goes inside the bearing, the big axial load from the Belleville washers overwhelms all the other loadings.

I made all the bearings an easy sliding fit, inside and out. This made it very easy to assemble but it went rock solid the moment I tensioned it.

How do you plan to mount the motors? I suggest you cobble them on somehow with plates and studding then replace everything when you have CNC. Motor mounting is important now only because it determines the length of the screw.

Things to remember when designing motor mounting plates...

Putting the motor on so it faces away from the machine is best.
Putting the motor on facing the machine saves a couple of quid on the ballscrew length but makes everything else difficult.
Leave a tadge of motor movement to adjust the belt tension.
Cut the outline for a belt cover and it's mounting bolts, assume you have CNC for making the belt cover.
Somewhere to attach a flexy conduit over the motor wires saves bodging it later on.