Re: ballscrew question,

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "David A. Frantz"
<spinwizard@f...> wrote:

> Hi Mark;
>
> Nope you don't need to support at both ends in all cases. Please

note

> the word ALL. In fact in some cases unless your alignment is
> spectacularly good it may do more harm then good.
>
> Dave

I agree and disagree.

If you have a 6 inch screw that is 10 times longer than the diameter
it will be hard to spin it fast enough to see any flexing.

I just picked the 10:1 ratio, it probably is different, but when you
have a 4 inch overhang of a 1/8 screw, (64:1) and spin it as high
RPM, ANY imballance will cause some deflection promoting vibration
and a further imbalance.

At low RPM the lenght/dia ratio could go higher without a problem.

The two Z's on my unit are 1/2-10 ACME and overhang about 4 inches.
(8:1) I don't spin over 1,000 RPM and have never experianced a
problem.

I think that at some ratio, the far end bearing will have little
effect as the shaft can bend to allow for any miniscule misalignment
whereas a short shaft would impart heavy pressures in any
misalignment. If you can flex it by hand, you must support it.

Dave

>
>
> On Wed, 2005-02-09 at 04:14 +0000, mark_anthony123 wrote:
> >
> >
> > hi, do ballscrews have to be supported at both ends? Is there a
> > certain length or rule of thumb? I was thinking of the z-axis for

a

> > homemade cnc router and the whole travel is only about 6 inches.
> > what about a 20" travel, the most the screw would be hanging out

at

> > the end is 10". support it? I was looking at a mill/drill plan

and

> > I did not see pillow blocks on the free end. Thanks Mark.