Re: [CAD_CAM_EDM_DRO] Z axis on the knee, how practical????

aaalfano wrote:

> Jon,
> How did you convert the quill on the Bridgeport with ball screw & ball nut?

I managed to obtain a surplus ballscrew of high quality. I looked at some
other retrofits, including Bridgeport's own Ez-Trak, the Anilam and such.
These all drive the quill on a standard J head from the hole that the stop
ring normally mounts to. So, I decided to duplicate the same setup with
the screw that I had. See http://pico-systems.com/zaxis.html for
some pictures, etc. The tough part of this is that the rounded shape
of the J-head and especially the belt housing were impossible to
measure accurately, and when I got the whole thing built, the encoder
on top had about 1/2" of interference with the belt housing. I should have
cut cardboard templates and test-fitted them before cutting metal. So,
I had to slot the two mounting holes and move the whole assembly about
1/2" farther out from the quill so the encoder would clear. I had not cut the
link that attached to the quill yet, so I didn't have to patch anything
there. I had made it extra long in case such a situation came up.

This contraption seems to have about .0012" backlash, due to flex in
the parts. Most of that is rocking of the link. the ballscrew doesn't
prevent the link from rocking a little, and the small area of contact on
the quill doesn't, either. I don't think it can be done much better than
this with this arrangement. So, I guess that is why the old BOSS
machines used a coaxial ballscrew drive for the quill.

Jon