Re: [CAD_CAM_EDM_DRO] Re: leadscrew bearings / machine design

r_fl_z@... wrote:

> 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.

There are two pretty standard ways to do this, and they work with radial
or
angular contact bearings, within the ratings of these units.

If the threaded part of the leadscrew is larger in diameter than the
ends, which
is common for machine leadscrews, then you can rest one bearing
against the turned flange this step provides. The outer housing can
have a
reduced diameter in the center of a bore that holds the bearing outer
races.
This provides a surface to accomodate pressure from two bearing outer
races pressing inwards on that step. Finally, a fine threaded collar
can be
provided to screw onto the end of the leadscrew to press the inner race
of the
2nd bearing toward the 1st bearing. This will allow you to preload the
bearing set until you get the desired end play - or wreck the bearings.
This is the scheme that is used on an ancient GE CNC axis drive that
I adapted to my mill, and also how I did the same for my Z axis drive.
It is what I've seen on numerous other leadscrew applications.

There is another way to do it, that may be simpler for certain leadscrew

configurations, especially with small diameter screws.
You have to make a sleeve that attaches to the leadscrew such that
it has a step of larger diameter in the center of the sleeve. Or, the
leadscrew could be made with this step in it. A bearing slides in from
each
end to rest the inner race against the step. These bearings fit into a
housing made of such a length that the bearing outer races are about
at the face of the housing. An end plate bolts over each bearing.
By placing spacers over the outside of the most accessible bearing, you
can adjust preload, as the end plate presses on the spacer, which
presses
the outer race deeper into the bore, pressing the inner race against the
step
in the collar.

I prefer the threaded collar as it allows pretty fine adjustment of the
preload.
It does require some tricky boring work to get a bore with a reduced
diameter step in the middle. It makes preparing the end of the
leadscrew
very easy, however.

Jon