Post date: Feb 2, 2014 4:32:06 AM
Alternately, "this guy sure loves drilling holes axially in rods/bolts". To illustrate why I say that (hopefully you can figure out where the axial drilling comes in):
This is more or less the culmination of trying to get my new leadscrews coupled to the steppers. In principle, it's a simple task- secure the screw to the bearing, turn down the end to 1/4", and connect to the stepper. I did this with the other axes, so why is it so hard now?
The issue is the acme nuts. 3/8" nut, 3/8" bearing- OK. 3/8" acme nut, 3/8" bearing- not OK. The acme nut is significantly larger than a regular nut. Of course it has to be just big enough to reach the edges of the bearing. In other words, there's no way to use the acme nut to clamp the acme rod to the bearing without interfering with the rotation of the rod. (The alternative would be to just not have the bearing secured, allowing the use of the acme nut and free rotation, but that's equally useless.)
The solution I've used is to basically create an intermediate piece to clamp to the bearing and the acme rod. This consists of a larger-diameter rod (actually a piece of a bolt) with a hole bored in one end for the acme rod and the other end stepped down to 3/8" (and threaded), then to 1/4" (for connecting to the stepper). Two set screws hold the acme rod in place. The result is basically a conversion to a standard fine-thread 3/8" bolt, which allows a normal-sized nut to be used to clamp to the bearing. Only one nut is required, since the other side of the bearing can be pressed against the shoulder. The whole setup can be seen above.
Thanks to doing just about everything on the lather, the results are very nearly perfectly axial.
I've also got holes drilled in the nut holders and angle aluminum cut to mount them to my axes. Just a few more steps before I can finally install the new leadscrews (and table!).... And yes, yes it is always "just a few more steps". That's how these things go.