RE: [CAD_CAM_EDM_DRO] Does this make sense? was Re:BentNookballscrews ?????

Kim -

So then by your wheel bearing example, if I adjust my wheel
bearings for 50 lbs of axial preload, then it would take an extra
50 lbs per wheel to roll the car? I'm not disputing that the drag
increases, but it is certainly not 1-to-1, and you must take into
account the moment arm length. You hit it on the head, though:
The drag force is roughly PROPORTIONAL to the preload, and the
proportion would be a function of the efficiency of the rolling
elements.

According to the formula that you read:

Td = (Kp*P*L) / (2*3.14),

where:
Td = preload drag torque (Kgf-mm)
Kp = preload torque coefficient = typically between 0.1 and 0.3,
I'll use 0.2
P = preload force (Kgf)
L = lead (mm)

Then:
For a 5mm lead screw with a 250 Kgf preload between ballnuts:

Td = (0.2*250*5) / (2*3.14)
= 39.8Kgf-mm
= 0.390 N-m
= 55.3 in-oz
= 3.45 in-lb

This torque would be a small fraction of the peak torque available
from the motors of a medium-sized mill.

I'm done.

Regards,

Carlos Guillermo
VERVE Engineering & Design

-----Original Message-----
From: Kim Lux [mailto:lux@...]
Sent: Tuesday, August 12, 2003 1:32 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Does this make sense? was
Re:BentNookballscrews ?????

Yes, I read them and I fully understand them.

Did you ever replace the wheel bearings in a car ? The two
bearings act
the very same way as the ball nuts do on a ball screw. When you
tighten
the preload the drag increases. The amount the drag increase is
proportional to the preload and in our case, with a 5 TPI ball
screw,
the torque required in inlbs is 1/31st of the preload in pounds.

Have you guys ever actually worked with a ballscrew and ballnuts,
applying preload ? I've set up 6 axes in the last few weeks.

Kim