Re: [CAD_CAM_EDM_DRO] 4th axis rotary table - suggestions?

"David M. Munro" wrote:

> Hello,
>
> For my BP cnc conversion, I was planning to fit a 4th servo to a
> standard
> (but good quality) rotary table. It has been pointed out to me that
> the
> backlash on a manual rotary table in going to do me in, and that I
> should
> consider using a rotary table specifically designed for CNC work. I
> was
> refered to the Servo-Systems table:

Depending on the construction of the rotary table, it may be possible to
tighten
up the gear engagement to reduce backlash. I got an ancient (1910
vintage)
indexing head that had a fair amount of backlash, and a very weak
spindle lock.
I decided to see how much I could tighten up the worm gear, as it had a
fairly
elaborate mechanism for adjusting the gear mesh. It had the whole worm
assembly (worm, bearing, and hand crank with the indexing plates) on a
pivot, and two setscrews that worked against each other to rock the worm

on the pivot. I just kept tightening it up until there was a spot with
the slightest
hint of binding. It is so tight, with respect to backlash, I absolutely
can't
tell, by trying to rock the chuck, whether the lock is on or off. There
must be
some backlash there, but it seems to be down in the arc-seconds region.

I can't say you'll get such a good result with yours, but it is at least
worth
looking into to see if the worm can be tightened up.

Jon