Re: [CAD_CAM_EDM_DRO] Re: Looking for short ballscrew

Greg Nuspel wrote:

> Jon,
>
> I see your point. Wouldn't it be nice if there was an easy/cheap way :-)
> From: "Jon Elson" <jmelson@...>

> > Greg Nuspel wrote:
> >
> > > What if you used a servo motor on the fine feed wheel input, but ran a
> cable
> > > to a clamp on the quill. This cable then runs over a drum attached to an
> > > encoder. Now you have no backlash in your system.
> >
> > Yes, you still have backlash! The encoder (discounting vibration of
> > the cable, nonlinearities in the wrap of cable on the drum, etc.) will
> > read true position, but the motor will have to rapidly jump from one end
> > of the considerable backlash to the other, causing a big bump every
> > time it gets to the other side. It will just bash back and forth .050"
> > all the time, knocking the quill up and down a few thousandths and then
> > reversing. This kind of mechanism will be a terrible pain to make work
> > at all.
> >
> > Jon

Unless you trip over one at a scrap yard, not likely. (But, it does happen,
maybe once in a lifetime.) I got off fairly cheap, but NOT quick! The
biggest difficulty was properly measuring the complex, curvy surface
of the Bridgeport mill's head. I wanted the ballscrew as close to the
face of the quill as possible. But, I got it too close, so that the encoder
would not clear! I had to convert tight holes into long slots to allow the
whole block to sit farther out. That made the whole thing a bit less stiff.
I paid $100 for the precision ballscrew, and then cut it an inch too short!
Fortunately, I had left some extra space in the original design, so I was able
to rearrange some of the pieces, put the sprockets on backwards and
such, and still get the full range of quill travel. It took a month, I guess,
of spare time to make the whole quill drive, and it pretty much worked
first time! I made a number of the parts with the mill in 2-D CNC
mode, and it was a blast to design all sorts of rounded shapes, and
parts with wierd angles on the sides, and cut them out in one fixturing.

Jon