RE: [CAD_CAM_EDM_DRO] Re: rolled ball screws

Any preload system should have a very high stiffness, much stiffer than a
wafer spring would allow. The perfect system would be no force on the
balls, with an infinitesimal amount of backlash. Then when under load, the
full force capability of the ball screw (hundreds of lbs force) is achieved
with only a tiny amount of backlash taken out. If the system will take 1000
lbs of force with a relative compression of only 0.00001", you have an
effective stiffness of 100,000,000 lbs/in as a spring rate. These are the
sort of numbers a solid piece of steel would provide. With such a system
you have no significant load on the balls when there is no load on the
machine.

On the other hand, with your wafer spring, you clearly have to compress the
wafer to a load as high or higher than the load you want to deliver with the
ball screw. If you don't do that, you will have backlash under load as you
load force exceeds the compression force on the wafer spring. Unless you
derate the ball screw, this will be several hundred lbs of force. The
compression distance required to achieve this far exceeds the normal
backlash, so the balls have to live with that force day in and day out, no
matter whether the machine is under load or not. The effective spring rate
of a wafer spring is probable two orders of magnitude less than that of
solid steel.

Bottom line is that a stiff system between the nuts allows for longer life
on the ballscrew without the risk of the working load overcoming the nut
preload system.

Greg

-----Original Message-----
From: Yesamazza@... [mailto:Yesamazza@...]
Sent: Sunday, January 26, 2003 1:03 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Re: rolled ball screws

Hi
I have not made a preloaded nut so this is only in theory but I think
you will be able to reduce the back lash further by preloading the nut using
a wafer style spring washer. There will always be some error in lead and
pitch diameter so if you take out all the play with a double nut that has no
"give" it will bind some were along the travel. If you adjust the nut to
min
clearance then use the preload to do the little bit of slack that's left,
your
system will be at its best. My 2cents Josh