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

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@...]
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.