Re: [CAD_CAM_EDM_DRO] Methods for ball screw driving Z axis on Bridgeport type quill

Robert Allen & Marsha Camp wrote:

> I am thinking of servo driving the Z axis on my current 3
> h.p. mill cnc conversion (x &y axis Gekko g320 servo drives
> and 210 in. oz. motors). The quill is similar to the
> bridgeport style, a pinion gear driving a rack on the quill
> and a quill handle but w/o a draw bar. The end of the pinion
> gear opposite the quill handle has a 3/4"x 6"L shaft that
> comes out the other side of the quill housing.
> Is there any workable way to drive the z axis through the
> pinion gear and get good 3 axis results, i.e. be able to
> mill profiles?

I seriously doubt it. Even if you could deal with the backlash,
(which I think is almost impossible) what is the accuracy of such a
coarse rack? I suspect it has cyclical errors of maybe 5 - 10
thousandths of an inch as it passes through the cycle of each
gear tooth. I removed the pinion and shaft to prevent it from
clunking around, and attached a ballscrew to the front of the
spindle housing. I made a bracket that goes from the ballnut
to the hole in the quill where the depth stop ring normally
is attached. I still get about .001" backlash, I think mostly from
the flexing of the bracket and a rocking of the ballnut.

> Any ideas on how to attach a ball screw to the quill?
> Besides the quill moving the whole quill gear box and motor
> slides up and down on a set of ways but it seems very heavy.

Well, this isn't made like a Bridgeport, then. But, a ballscrew
should be able to handle it just fine.

Jon