Re: Ballscrew bearings

stratton@... wrote:

> From: stratton@...
>
> I know in an ideal world I'd have the space to mount (and the cash to
> pay for) a pair of the premanufactured ballscrew end blocks. But I
> don't, so I'm trying to come up with a smaller, simpler, cheaper
> alternative that will still give acceptable performance on a lathe
> crosslide, which doesn't need to move very fast.
>
> Basically, one bearing assembly is going on each end of the screw.
> The operator end bearing goes in a housing that screws into the
> carriage so it is adjustable to preload the ballscrew.
> For the bearings, I'm considering (at each end):
>
> "Duplex angular contact ball bearing" (the $16 kind, not the $160x2
> matched pair kind)

This is the best, but use it only at ONE end of the screw. Use a simple
ball bearing
at the other end to prevent vibration of the free end. On short screws,
there is no
need for that, either. But, you don't want to constrain the screw
between two sets
of angular contact bearings, as it would either bow the screw, or
whatever the
screw is attached to. You put the bearings into a block with a shoulder
in between
the bearings. Then, you have a collar that squeezes the inner races
together, providing
whatever level of preload you need to remove backlash.

I used this approach in the Z axis on my mill, and it has been working
very well.

> A normal ball bearing and a needle thrust bearing

You'd really need two thrust bearings, and they are not the best for
this application.

> A tapered roller bearing (if I can find one with a 1/2" bore)

These are generally not available in small sizes, although some do
exist. In the
smaller thrust ranges, angular contact bearings provide much better
performance
(ie. less drag).

Jon