Re: ballscrew preload torque drag, was: Bent Nook ballscrews ?????

Carlos,

Excellent post.

The gothic arch threadform used in ballscrews (and linear bearings)
is designed to cope with the deformation of the balls as
they "squish" into an oval shape... This deviation from round is
where a large part of the increased drag comes from, and is what the
gothic arch attempts to deal with by ensuring that the oval balls
will keep ROLLING, and not skidding... Newer shapes have been
developed and are used for the same reason.

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Carlos Guillermo"
<carlos@v...> wrote:

> Kim -
>
> Preload is an axial load, but it is balanced within the ballnut
> setup. It is not seen directly by the motor. What the motor sees
> is an increase in the torque required to spin the screw, due to
> the rolling efficiency of the balls, which is pretty darn good (on
> the order of 99.96%; depends on load). So the factors in your
> torque drag equation are mainly: overall efficiency, axial preload
> force, and pitch diameter. As an example, just imagine if you had
> 100% efficiency, you could put all the preload you wanted in the
> ballnut, and you wouldn't need any extra motor torque to spin the
> screw.
>
> Check out this link:
> http://www.ruchservomotor.com/PDF/H_Ballscrews(full).pdf
> It has 106 pages of ballscrew info. Page 28 has the equation for
> preload drag torque.
>
> Regards,
>
> Carlos Guillermo
> VERVE Engineering & Design
>
> -----Original Message-----
> From: Kim Lux [mailto:lux@d...]
> Sent: Tuesday, August 12, 2003 8:01 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Does this make sense? was Re: Bent
> Nookballscrews ?????
>
>
> NO. THIS IS WRONG. The mathematical equation describes the
> relationship between axial loads and torque. Preload is an axial
> load,
> pure and simple. Torque = axial load x constant, pure and simple.