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

Ballendo:

I've uploaded Lead screw bearing stackup 3.gif, version 3 of the
proposed stackup. Now this design seems fully constrained and
buildable. See what you think. See comments below.

--- In CAD_CAM_EDM_DRO@egroups.com, ballendo@y... wrote:
> Ron,
>
> That helped. The part that is confusin' for us "been there's" is
that
> the scale of your drawing is "too tall, not wide enough"> If
> you "squeeze" it from the top and bottom, while you "stretch" it
from
> left to right(until each "bearing" box is about square) you will be
> closer to what the "typical" is.
>
> So the bearings will look more like (angular contact on right):
> _ _ _ __
> |_|O|_| |_\O\_|
>
> _ _ _ _
> |_|O|_| |_/O/_|
>

Understood. I've changed the representation of the bearings in this
version.

>
> Now that thats covered, lets see whatcha got:
>
> Method A appears to be correct. As you (and I) mentioned, this one
> can easily wreck bearings. But it IS used a LOT on lower end stuff.
>
> Adding a spacer collar(simple cylinder, no step) between the
bearings
> (inner races) makes this a much better system! This is also the one
> where the internal "step" can be a sleeve fastened into the
straight
> bore.
>

Ahhh..very interesting. How does one go about fastening the
internal 'step' sleeve in the straight bore?


> Method B appears to be close to what Jon E described.
>
> (I believe he was detailing a method to use when you have a small
> dia. screw, or don't want to machine the ends of the screws) In
this
> case, your spacer collar will actually fit OVER the end of the
> UNMACHINED screw.
> (like an old potentiometer shaft extension, for you radio guys :-))
>
> The way you have drawn it(which will work): There is no need to
> reduce the diameter of the leadscrew for your "spacer collar" to
have
> a step. Again a simple cylinder spacer will suffice.

I've changed the collar from a T-section to a simple collar. However,
is not the lead step still required to react the load through the
bearings (axial) when clamped up?

>
> You didn't draw the one I spent a thousand words describing? :-)
> Functionally, it will be like method B. But MUCH stronger, unless
> the "cover" Plates are "real thick".
>
> If you look at method B and assume one of the housing cover plates
is
> just part of the housing, and the other cover plate is the camera-
> lens nut, you'll have it, I think.

Take a look at version 3. It seemed economical to incorporate one of
the bearing retention plates in the lead/guide support plate.
>
> Remember, both of these would be considered "rigid" mounts, since
the
> bearings are spaced. Method B really needs a spacer between the
outer
> races of the bearings. To be REALLY rigid, that is; it WILL work as
> drawn.
>
> Hope this helps.

Oh, YEAH. It's helpin :)

>
> Ballendo
>
>
> P.S. I just searched online for a link (or links) to post for this
> thread. Came up empty!(was very surprised) All the major
> manufacturers DO indeed show only the screw stack or "cartoons".
> Several years ago this was not the case! I wonder if too many
people
> were makin' their own? :-)
>
> Another thing I noticed during the search is that most mfr's were
> showing fixed instead of rigid. Maybe just because the block (and
> materials) cost less; maybe bearings are better??
>
> Anyone else find a link to post showing the three std. end mounts?