Re: [CAD_CAM_EDM_DRO] Lead screw/Guide rail install/pre-load

In a message dated 10/25/2000 11:11:20 AM Hawaiian Standard Time,
r_fl_z@... writes:

<<
My thinking is that this arrangement for the lead screw and support
rails will provide adequate support while preventing thermal effects
from deforming the linear elements.

Does this sound reasonable? Any alternate plan suggestions would be
sincerely appreciated.

Best regards,

Ron >>


Ron,

I don't recall what kind of machine this was. If these parts are close to
a plazma head and are subject to hundreds of degrees (not a good thing) ,
then thermal expansion will be a serious problem. If this is a system for a
machine that has virtually no thermal effects such as a pick and place
machine, then almost no precautions need be taken. If your linear elements
are of the same material as your machines structure, then linear expansion
will be very similar.

The only problem I have had is thermal expansion on long ballscrews. After
a few hours of cutting a job, the cutter did not exactly retrace a previously
cut surface. So, as I spiralled down into a 14" long bronze plaque, I had
small stairsteps around some of the letters. These were only noticeable at
the end farthest away from the fixed end of the ballscrew. Turns out I had
excess preload that caused heat generation on my x axis screw. I also changed
my machining strategy so I do a very fine finish skim cut after roughing is
complete. Fixed both, no more problems.

The magnitude of the problem may be overestimated. IMO.

Peter
THRD, Inc.