Re: dans' mill/drill quill retrofit

Ballendo,

Yeah, assuming the lathe is accurate.....that's a big assumption.
That's why I was curious how he did it.

Checking ball screws reminds me of an incident about 15 years ago.
I had purchased a new CNC lathe and wanting to be sure it'd do
everything I wanted I setup up a spec sheet which I expected the
machine to perform to. The dealer accepted my specs which he said
were no problem for this machine. Right off, it was apparent the
machine wouldn't position closer than about +/-.0003" in the Z axis
with a load on it. That was out of spec.

They sent a tech out to check the ball screw. The dummy forgot to
bring his measuring equipment. So he borrowed my Starrett long
travel dial indicator. He plotted "screen" position versus indicator
reading over 3 inches. His chart showed substantial error in the
screw. They ordered a new Z axis screw, around $1500 for the screw
w/nut. Plus 12 hours of the tech's time.

The new screw didn't cure the problem. The problem was a loose
mounting of the tool turret.

The moral of the story is you can't check a super precision ball
screw with an uncalibrated dial indicator.

The dealer had to eat all the costs for this fiasco after the factory
verified the original screw wasn't bad.

thanks,

Doug

--- In CAD_CAM_EDM_DRO@y..., ballendo@y... wrote:
> Doug,
>
> I'm not Dan, but I can think of a few ways...
>
> Easiest would be to put the lathe in "threading mode" (at the same
> tpi as the ballscrew). Mount an indicator in place of the threading
> tool, and set it 'riding' on one flank of the ballscrew. The
> ballscrew is mounted in a collet/chuck of the lathe. Far end of
> ballscrew supported by a live center).
>
> Now you can turn the lathe by hand(or slowly/ carefully under
power),
> and see any pitch variations reflected in the indicator reading. Of
> course, this assumes the LATHE is accurate!
>
> Hope this helps.
>
> Ballendo
>
> >Just curious...how did you use your lathe to check the pitch?
> >thanks,
> >Doug