Re: Linear bearing types?

Geoff Roehm wrote:

> From: groehm@... (Geoff Roehm)
>
> Hi! Just got switched over to digest - thanks, Bill - Great list!
>
> I've been sneaking up on this CNC thing for a few years, and have
> the electronic part more-or-less less figured out.
>
> What I'm having a problem with is the mechanicals, specifically
> whether to design and build a machine, or just buy an old CNC mill
> and retrofit it. From the prices I've seen for accurate linear
> bearings, shafts, ballscrews, and machining, the cost would be
> about the same.(?)

Right - and you'd have a very flimsy machine, which wouldn't be able
to cut anything tougher than cardboard or modeling wax. Some people
want a machine like that. But, as a (converted) Bridgeport user, who
still has problems with rigidity sometimes, I can't imagine how something
with 1/2" or 3/4" round rails would work for metal cutting.

I do have a photoplotter with 1/2" round rails, and it has some vibration
problems that require damping. It has an optical carriage that weighs
ounces, and no cutting forces at all!

> Anyway, what I'm wondering about is maybe pouring linear bearings
> around semi precision shafting. I've thought about babbit, and just
> heard about this stuff called Moglice. Any ideas?

Well, the puored bearings would wear quickly, and it doesn't sound
like there would be a way to adjust play. but, flex in the shafting
would make it a very inaccurate machine.

Jon