Re: [CAD_CAM_EDM_DRO] Re: Driving a Bridgeport Knee

----- Original Message -----
From: "Polaraligned" <polaraligned@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, February 14, 2005 5:20 PM
Subject: [CAD_CAM_EDM_DRO] Re: Driving a Bridgeport Knee


>
> Well, I don't think they get it very much below .001". You will
> have backlash to contend with. But the bigger question is how
> accurate are those gears anyway? People get ground screws over
> rolled ones- yet settle for sloppy bevel gears? I just like the
> idea of driving the leadscrew directly and saving the bevel gears
> for manual operation of the machine. I may even get a ballscrew
> for the Z axis, but I have not really decided if this is just a waste.
> As it is all commercial conversions (that I have seen) drive the quill
> because it is more accurate. To each his own...
>
> Scott
>

Do not think that you get good accuracy by driving the quill. I have
a Bridgeport conversion mill that drives the quill and have about .004
backlash. I have been through the whole thing. The problem is that the
attachment between the quill and the ballscrew is by a long yoke that is
bolted to the side of the quill. It is a long lever attached by two
closely spaced
bolts. Everything is tight and the ballscrew is in good shape. There
is simply no way to drive the quill without having a less than ideal
system that is subject to flexing.

Driving the knee may have it's own problems but driving the quill
with some add on mechanism pretty big problem itself.

Pete.