Re: [CAD_CAM_EDM_DRO] bridgeport quill screww

Zafar Salam wrote:

>Hi,
>
>A question for bridgeport retrofitters. What size ball screw is suitable for the bridgeport quill. I have mechanized the knee of my bridgeport clone and now I am planning to put cnc on the quill too. I have a couple of 5/8" and 1/2" ball screws with nuts. Would these be enough or I need heavier screws.
>
>

I'm using a roughly 3/4" 10 TPI ballscrew on the quill. I believe it is
a HiWin screw, but
it has no markings or logos on it. The Bridgeport power feed oveload
clutch is to be
set at 200 Lbs linear thrust, so you don't need the same kind of linear
force as the
X and Y screws there. The 5/8" ballscrew should be fine, and even the
1/2" will likely
do fine. If you look up the ratings of these, they are certainly strong
enough. But, ball
bearing life and accuracy scales inversely with load.

For a quill rig, the most important things are rigidity, and keeping the
screw as CLOSE to
the quill as you possibly can. A 2" separation between the screw and
the quill is about the max
you want. If they are too far apart, flexing develops and causes the
backlash to get large.
That's why Bridgeport came up with the insane coaxial quill drive used
on the BOSS machines.
VERY expensive, hard to work on, but it WAS unbeatably rigid.

Jon