Re: [CAD_CAM_EDM_DRO] Re: Bridgeport Tracer?

> Since the machine was essentially unused we wanted to check the
> accuracy of the screws. As near as we could determine there was
> about .001" backlash. Not CNC accuracy, but good enough to convert
> to a nice manual machine.

You might want to track down the source of that backlash.

A single ballnut running on a ballscrew will usually show slight
backlash, so two nuts are used on zero-backlash machines, with an
(often adjustable) preload mechanism between them.

You might want to see if there are two nuts - if so, the preload me be
out of adjustment. If not, you might be able to find a way to put a
second nut in, or reload the existing nut with slightly oversize balls
to decrease the backlash even further.

Also, don't rule out the possiblity of the screw sliding in the
bearings if something is loose .

Incidentally, if you have ballscrews you will need something to apply
drag to the screws to use the machine manually - otherwise you may
backdrive the screw with cutting force. You can engage the locks for
every axis but the one you are cranking - and perhaps you should for
best accuracy, but it could be annoying for those quick 'eyeball' 3-axis
jobs.

In some stepper CNC conversions, the cogging of the stepper
(especially when timing belt reduction is present) provides enough
drag when powered off to permit manual use. That was going to be the
plan for the ballscrew crossfeed on my 13" south bend.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT