Re: [CAD_CAM_EDM_DRO] re: torsion in long leadscrews wasRe: Servo torque test question

> Les W wrote:
> >The seal friction terminates the screw in its characteristic
> >impedance to prevent large torsional resonances in long screws.
>
> Les, List,
>
> Another approach used with long screws is "fix the screw in position,
> and spin the nuts...
>
> Ballendo
>

Very true! Among the acres of gantry cnc routers at IWF this year many used
rotating nuts.

I did not of course on mine. I designed it a couple years ago
and well... just plain didn't think of it.

The ballscrew will still have torsional resonance though. The reflected
phase will just be reversed.
But there are great advantages in moment of inertia and critical speed..
Ballscrews account for about 30% of my total inertia here.
I should also note that torsion has almost no effect on accuracy. I minimise
it due to ball dither/scuffing issues.
I read it can cause brinelling in four point contact ballscrew types.

BTW I have a pc 690 router for hand use but have never taken it apart.
What's in there... 62xx abec-1 deep groove? I have a bearing order for other
stuff and ought to get some extras, perhaps abec3 or 5. They do have higher
dn capability. Pc's
bearings may have a different internal clearance spec as high speed bearings
often do. It's kinda on the outer limits for grease lubrication too.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html