Re: re:Final leadscrew design - thanks to all (not yet?!?!)Done

Ballendo:

What process allows you to determine the torque on the lead nut? This
load must be related to the clearence between the bearings and
preload, no? These details will be uninspectable on assembly, right?

Thanks,

Ron

--- In CAD_CAM_EDM_DRO@egroups.com, ballendo@y... wrote:
> Ron,
>
> That one will work. And the proportions are close. You could use
> bolts and nuts to avoid any tapping(for the retainer plates)Good
work!
>
> Addt'l replies below
>
> Ballendo
>
> >The comments on the preload and the grinding of the bearing
> >pair to a matched set was a little beyond me.
>
> Preload is just a different way to say "less than zero clearance".
So
> you start with "slop, or play", and you reduce it until it is gone;
> which is zero clearance. If you then reduce it some more, the parts
> are pre-loaded.
>
> The face grinding of the bearings is done by the manufacturer to
> create this zero clearance or pre-load.
>
> Let's pretend you wanted to do this yourself:
>
> You take a plain bearing and the inner race moves(in relation to
the
> outer race) thrust-wise some amount; let's say it's .003 (pretty
> typical for a small bearing)
>
> Next you set some emery paper on plate glass and "face grind" .003
> from the outer race of this bearing.
> (The inner race will "float" since it can rise .003 working only
> against gravity (mostly) and so will not be subject to much, if
> any "grinding")
>
> Can you see that while it is placed with the "ground" side down,
> there will now be zero clearance?
>
> But if you turn it over, it will still have the .003 movement?
>
> Do this with two bearings, and put the "face ground" sides
together,
> and one bearing will keep the inner races from moving one
direction,
> and the "matched" 2nd bearing will prevent movement in the other
> direction.
>
> Now if we "grind" a little MORE... say .004 from each bearing
> (we're assuming each bearing has .003 clearance(end-play).
>
> We find that the bearings must be "squished" together for that
> last .002 between them! THIS IS PRE-LOAD. Now we know that any
force
> LESS than what we used to "squish 'em together" will not cause any
> thrust-wise(axial) movement!
>
> >The final FIXED mount will require simple shimming under the lead
> >nut, at most, to remove any play, per the Ballendo directions
early
> on, <snip>
>
> Actually, the "shimming" will be BETWEEN the bearings (only for
> the "cheap" plain bearings). What we're doing is realising that it
is
> easier to "take up the slop" with shims of the inner race, rather
> than going through the "grinding" of the outer race described above.
>
> Hope this helps.
>
> Ballendo