In this thread,
http://madmodder.net/index.php?topic=6264.0 , I described bodging up a cam disc to operate a half nut on a baby lathe which until now had a solid nut on its 1mm pitch leadscrew, making it a pain to reposition the saddle over anything but a short distance.
I’ve finished the project now, and it’s shown at
http://andysmachines.weebly.com/a-half-nut-for-the-perris.html In doing it, I learned something. I thought that with a 60 degree thread, the nut might bend the leadscrew upwards in use. Surprisingly, there is no tendency for the leadscrew to flex away from the half nut under pressure from the cut. Indeed, when the leadscrew is turning, the nut will not drop out when the cam beneath it is turned to the disengage position. I think this must be because, though the forces on the threads at the bottom of the U shaped nut try to push the nut off, the forces at the tops of the U act horizontally and are more powerful, so the nut stays in position without any support from the cam. To achieve disengagement, I have had to incorporate a fix whereby the cam would not only push the nut up, but also give it a slight pull downwards to unstick it, after which some little springs I incorporated took it the rest of the way down.
The corollary of all this is that because the nut wasn't being pushed down, it follows that the leadscrew wasn’t being bent upwards, either.
Andy
