RE: [CAD_CAM_EDM_DRO] Preloading ball screws

Hi Bill -

I see a problem with that arrangement. The spring-loaded ballnut
would not be backdriveable in its mounting threads, so although it
would tighten up the nuts against each other on the areas of the
screw with lower pitch, it would not allow the nuts to open up on
areas of the screw with higher pitch. You would not have constant
preload, just a system that eliminated backlash, but then caused
potentially excessive ball contact forces when the screw pitch
increased.

Regards,

Carlos Guillermo
VERVE Engineering & Design

-----Original Message-----
From: Bill Kichman [mailto:billkichman@...]
Sent: Friday, September 26, 2003 7:21 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Preloading ball screws

I am sure this has been covered ad nauseum, but here goes...I have
2
ballnuts threaded into a steel block which is attached to my table
for my
ballscrew conversion...I had been depending on rigid backlash
adjustment by
simply screwing one of the nuts tightly against the other, and
tightening
both setscrews. As I understand it, a spring type arrangement is
more
advantageous due to wear issues which act to change the fixed
preload over
time.

My question is this....as I have no room whatsoever on at least
one of the
axes for adding anything to the periphery of the nut, and the
threads
already are there, would it be reasonable to attach a strong
spring such
that it would act to tighten the threaded ball nut's threads at
all times?
That way, the spring wouldn't have to be nearly as strong as an
installation
without the threads installed and a heavy spring arrrangement
in-line with
the nut. Am I seeing this clearly? The spring could partially
wrap around
the nut and keep a constant preload.
Has anybody done this?
R. William Kichman, P.E.
Kichman Engineering Associates
103 Old Furnace Road
Cornwall, PA 17016-0643
tel/fax 717/270-0714