Re: Linear bearing types?

Ian:

In response to your post here about babbit bearings, I have worked in
the past most extensively with babbit. Before I became a toolmaker, I
was a journeyman and used to use a lot of machines that were equipped
with babbit bearings and the such. I used to pour the bearings and
machine the bearing as well after pouring.

My comment is this. Having worked so much myself with babbit, you must
have the lead at the right temp. to pour and make a "good" bearing. I
believe we used to pour at around 350deg C to ensure a solid pour for
the bearing and the consistency. The machines that we had the babbit
bearings on were larger engine lathes, swinging approx. 60+ inches and
located in the headstock where we weren't turning the spindle all that
fast. Truthfully, after seeing the amount of rigidity that is required
for CNC applications in the rigorous movement of the axis' at the given
feed rates, I don't feel babbit is the best way to go.

Each application is different for each of our uses, and if babbit will
suit your application, and give you the tolerances required, then by all
means if you see fit, use it. This was just my opinion and not criticism
in any way.

Regards,
Don Hughes

> Poured lead or type-metal bearings are still used extensively on some
> older-type industrial machinery and they are very successful - hence
> there are machines around here still running with them which are over a
> hundred years old. One particular machine I can think of is a
> file-cutting machine where the leadscrew nut is actually a split brass
> block hollowed out to form a permanently in-situ mould which is filled
> with lead. In production work, where the machine is subject to
> continuous severe vibration as the chisel strikes the steel file blank,
> these cast bearings last several weeks before needing re-casting which
> is then a simple matter of cutting off the old lead and remelting and
> re-pouring it - about 5 minutes work and you again have a precision
> fitting new feed nut. While there obviously would be some wear over a
> period of time I don't think this should be a problem as, whenever you
> want to do a really precise job, you can just cast a new nut before
> starting. It also has the advantage that, if you set the carriage
> position before casting, you shouldn't have to readjust the machine for
> screw rotation on the new nut. If you use lead, it is also somewhat self
> lubricating - if you can still get lead that is, in this age of terror
> over using anything useful!
>