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

>
> What program do you open it with?
>
> -----Original Message-----
> From: r_fl_z@... <r_fl_z@...>
> To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
> Date: Tuesday, October 24, 2000 1:52 PM
> Subject: [CAD_CAM_EDM_DRO] 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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> [Non-text portions of this message have been removed]
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>
> Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the discussion of shop built systems, for CAD, CAM, EDM, and DRO.
>
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