Re: leadscrew bearings / machine design

Ballendo :)

Informative response. I agree that due dilligence can divulge many
design detials, but not all. For instance, it is still unclear to me
what the exact stack-up for the lead screw end away from the motor
looks like. I understand the screw strength and stability issues as
relates to the fixation method. As a result, I plan on using a
double bearing within the common bore as you described. It is not
clear to me what you are saying about the shim washers. I expect
that a spacer would be required between the bearings in order to
bring them flush to the surface of the plate they are mounted within.
What I can't seem to get is exactly how the bearings are retained, or
the load path to remove the thrust load.

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.

Thanks for your time.

Ron

--- In CAD_CAM_EDM_DRO@egroups.com, ballendo@y... wrote:
> Dennis wrote:<snip>A better design is to use two angular bearings,
> >but the cost is considerably higher. Each bearing costing about
> >12.50 each and two required per lead screw.
>
> Hi all,
>
> Radial bearings are much cheaper and CAN be used in thrust
> applications. Typical THRUST rating is one-half the AXIAL rating.
>
> Use 2 with shim washers (.001-.002 typ.) between to make a FIXED
> style mount for a leadscrew. Both bearings in a common bore/housing.
> A single radial bearing at the other end of the leadscrew for
support
> (if necessary).
>
> 2nd tip. Ask YOUR SUPPLIERS what is COMMON, before specifying a
> bearing(or other part). You may find that the industrial supplier
> near you has "stocked up" to supply some mfr. or provide
replacement
> parts very near to what you need. At greatly reduced cost. For
> instance, a 10mm bore(.393) may be a much different cost(more or
> less) than a 3/8(.375). Same for O.D., or thickness. You can
probably
> change the design to use either one, if you do it BEFORE you build
> the part(s) you have designed.
>
> Even the national suppliers, like Stock Drive and Grainger(Berry)
> often have SIGNIFICANT price differences between nearly identical
> parts. Same holds true for electronics.
>
> Common sense really, but often overlooked by a do-it-yourself-er.
Or
> someone working from a plans set.(be sure to get approval from the
> designer if you change the plans, though! He/ She may know
something
> you might be missing!)
>
>
> Hope this helps.
>
> Ballendo
>
> P.S. Recently there have been a lot of questions re: Machine design.
> And common practice(s).
>
> IMO, the best way to find this info is to look at the solutions of
> others. Dennis has a number of pics on his site, but don't stop
> there... There are HUNDREDS of pictures(details and over views)on
the
> internet of cnc machines! Home-made and otherwise.
>
> Also get the component part mfr. catalogs. Ballscrews, linear ways,
> motors, etc. The wealth of info here is incredible.
>
> Lastly, peruse the sales literature for the commercial machines.
> Often they will attempt to distinguish themselves by listing and/or
> explaining what special features or solutions they have found/used
> for common problems. Even if their solution is out of your reach,
the
> description of the problem solved can be very helpful. And help you
> know what to look for as you continue your learning...