re:Re: leadscrew bearings / machine design

Ron wrote:

>It is not clear to me what you are saying about the shim washers. I
>expect that a spacer would be required between the bearings in order
>to bring them flush to the surface of the plate they are mounted
>within. What I can't seem to get is exactly how the bearings are
>retained, or the load path to remove the thrust load.
>
>Unfortunately, the manufacturers seem to show cartoons of common
>bearing arrangements, but they ommit the entire stackup...showing
>only the lead screw and the bearings. No retainment details are
>provided.

Ron,

The shim washers are needed to take up the "clearance" within the
radial bearings. All "normal" single race bearings have this clearance
(manufacturing tolerance). Angular contact bearings designed for use
in thrust loads are ground so that when the inner race and outer race
lie in the same plane(as they will be in a machine mount) this
clearance is reduced to zero.(or some pre-load value)

Let me say this another way. If you take a standard radial ball
bearing and hold the outer race between you thumb and forefinger, you
can take your other hand and grip the inner race, and "move it
slightly" back and forth (axial, or thrust movement). This is the
result of the balls not being EXACTLY the right size to "take up" the
space between the inner and outer race.

Now, if you lay this bearing on a flat surface, the inner race will
still "move" up and down, due to this clearance.(you just can't grip
it anymore :-) ) If you put the "right amount" of shim washers
against the inner race(under the bearing) you will reduce this
clearance to zero. This is what the face grinding of the expensive
bearings does.(by removing material from the face of the outer race)

So, if you use two common radial bearings(to save money) you need to
shim the space between the inner races until zero clearance is
achieved and there is no backlash. You can also put in "a little
more" than what is needed for ZERO clearance.(this is pre-loading).
Be careful! It is easy to excessively "pre-load"!

Hope this is clear.

Ballendo

P.S. Get the literature from the "most expensive" suppliers! They
have more money to spend on it, and more need to "convince" you to
spend your money on their offering!

What I'm saying is that the details you seek ARE available, but maybe
not where you're looking. Just looked at a Ball Screws and actuators
catalog. It has DETAILED drawings of the end mounts. Lintech's
Ballscrew catalog has the "cartoons" you speak of, and although I CAN
see what they mean, I can also see that a newly introduced person
could not get the details from what they have presented.