Re: leadscrew bearings / machine design

Hummm...I just downloaded it and viewed it with no problem. Anyone
else have trouble with it? Apologies if my stupidity is wasting your
time :o

--- In CAD_CAM_EDM_DRO@egroups.com, "Smoke" <Smoke@5...> wrote:
> Help! I downloaded that file out of curiosity and when I opend it
all I got was a totally black picture!
>
>
> -----Original Message-----
> From: r_fl_z@h... <r_fl_z@h...>
> To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
> Date: Tuesday, October 24, 2000 5:16 AM
> Subject: [CAD_CAM_EDM_DRO] Re: leadscrew bearings / machine design
>
>
> Jon:
>
> I have uploaded a file called Bearing_stackup.bmp in the files
> section. It contains my interpretation of your description for two
> possible lead screw thrust bearing stackups. (sorry about the size)
>
> Method A:
> If this is correct, then I agree that the double counter bore would
> prove to be a challenge for me to build. Especially since I planned
> on enforcing concentriciy of the holes through the lead/guides
> support plates by drilling them simultaneously. As I understand the
> method A stackup, I'd have to drill the support plates and then
> locate the hole center on the thrust plate to perform the counter
> bore operation. Probably beyond my megar construction skills and
shop
> of tools consisting mostly of different size rocks :}
>
> Also, because there is no direct load path from nut to the sholder
on
> the lead screw, I can easily see how the assembly would eat
bearings
> if not carefully adjusted. With no spacer, one bearing takes all of
> the axial load...which depending on wether the screw is in tension
or
> compression. Correct?
>
> Method B:
> Now this looks pretty good to me. Easy to bore the clean hole, as
you
> mention. I would think that this arrangement could be improved by
> inserting a spacer between the two outer races. With the proper
> shiming and adjustment, the load path would be continious for both
> races, and the axial load should be shared equally between the two
> bearings.
>
> What do you think? Are the stackups correct?
>
> Once again, thanks to all who have addressed this issue.
>
> Best regards,
>
> Ron
>
>
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:
> >
> >
> > r_fl_z@h... 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
>
>
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