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

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.

Ron
bryan b <bjbourg@...> wrote:


Ron,

Seems like the the machine you mention has one thing in common with
Steve's and mine; the three have been apart and put back together
(incorrectly, I think).

I bet the proto trak you mention is also a Southwest Industries
product, like mine. I called them to get an idea about the machine and
the controls when I bought it, and an 'old timer' who was around in
the mid '80s answered some questions for me. The control was a 6502
processor el-primitivo, didn't even have a serial connection. Thats
when I decided to go with a Gecko 320 and DeskCNC setup.

SWI is on my to-call list as soon as I can get them on Monday, but I
bet I get a better answer here.

Bryan

--- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers wrote:

>
> Yes if the screw is making a linear movement and the table
stationary there is a problem. The way mine is its just a cross block
consisting of two ballnuts and two ground ballscrews. All of the
backlash adjustment is taken up with shims behind the bearings on the
endplates. The b'port I ran with ballscrews manually was an old
machine that they had retrofitted with a Proto-trak control and then
removed it and put it on a new B'port. So, I quickly claimed the
manual with the new ballscrews thinking it would be better. I didnt
like it for manual machining at all. It never felt like i had real
good control of it through the handcranks. Spongy and if an endmill
grabbed the work it would actually push the table and feed the
ballscrew. The thing was downright dangerous. There was no backlash,
it was just spongy under load and not very responsive.
>
> Ron
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