Re: [CAD_CAM_EDM_DRO] Re: How does one adjust Ballscrews on a Bridgeport

R Rogers wrote:

>Bryan,
>
> One thing I've noticed from using and talking to users of any Bridgeport series 1 or 2 as a CNC platform as in the case of the proto-trak they will not mill a perfect circle. I've never seen one that would. In theory it should but they dont. They always eggshape on the X axis. Circles will always be out a few thous or more depending on the age of the machine. I remember we bought a brand new Proto-trak and it eggshaped circles right out of the box (we had 4 other proto-traks that displayed an identical result). It shouldnt and I think the cross-block may be the culprit. They mount in a rather unorthodox attitude in the saddle and are prone to deflection. I'm sure some will disagree with this but I personally have never seen a Bridgeport retrofit (prototraks included) that had perfect radial motion. The interacts were built from the ground up for CNC and were much better about this. Sometimes we expect results that the machine was never designed to deliver. I wish they would, I
> could stop buying all these expensive large diameter reamers. And mothball my boring heads also.
>
>

Well, that's really interesting. We have some Bridgeport EZ-Trak
machines at work, I'll have to
see how well they do. I did my own conversion on a VERY old Bridgeport
machine, and the only
problem I see is backlash. It is about .001", and for my purposes not a
big deal. I DID,
however, replace the "yoke" that holds the original Bridgeport nuts. It
just looked too flimsy
to me. I do know that my yoke got loose back in the pre-conversion
days, and I immediately
felt it in the hand cranks. I turned the Y handle, and felt a bump in
the X handle. So, I had
to slide the table over and tighten it up.

Besides the backlash that puts little bumps at 4 points on the circle,
there is no egg-shaped
error. I do have high accuracy ground screws that are within .0001" per
foot, as verified
with gauge blocks and a tenth-reading DTI.

Jon