re:Re: leadscrew bearings / machine design(2nd gif dwg)

--- In CAD_CAM_EDM_DRO@egroups.com, JanRwl@A... wrote:

> Sorry to disagree with learned wizards, but, though very, very

stupid and

> very, very, very ugly, I had been there, done that, and the most-

rigid and

> "bestest" way to do the ends of a lead-screw are to have two

SEPARATE

> angular-contact bearings on EACH end (total, four per screw!), each

pair set

> at least twice the screw-major-diameter apart (between them), or,

at least

> twice major screw-dia. plus one bearing-thickness "on-center".

Really!


Agreed and understood. The degree of constraint for the bearings
will be a function of the length of the screw, the load, the speed of
the screw, and the desired accuracy...which is machine and
application dependent.

I am principly concerned with documenting traditional bearing
installations in practice today. I'll then be in a position to
massage the trade-offs of stability and accuracy vs. cost.


Just

> havin a pair of bearings with "no" space between them (oh, maybe

just a

> spacer between the two inner-races) is no-where NEAR the same as

the

> "spaced-apart" pair! Unless you are talking a total screw-length

no more

> than, say, ten times the major-dia.!

Roj. The greater the moment generated at the constraint point
(bearing plane) the more stable the system. Check out Lead screw
bearing stackup 3.gif in the files section for the latest fully
constrained design.