Re: [CAD_CAM_EDM_DRO] Custom made bearing for lathes

Matthew Tinker wrote:

> This subject was discussed at length on the "Quorn universal cutter and grinder" group. Nobody got it to work!
>
> Matthew
>
> Cristi <wtherapy@...> wrote: Hello,
>
> I wonder if it is possible to built with hobby machines a lathe air
> spindle or a fluid spindle for a lathe. I am interested in this
> because of the very high truth of running of these bearings (
> especially air spindle / bearings ). I don't want the lathe spindle to
> run at high rpm ( 4000 - 5000 rpm would be the maximum ).
> I know most of the air spindle tools are tiny and dedicated to small
> and precision works, I guess a lathe chuck would be to0 heavy / big
> for this?
> Has anyone tried this thing? What would be the cost / effort to do this?

There was an article in home shop machinist several years ago.
Some fairly crude procedures were used, and the author said it
works. I think a good home shop guy could actually do better.
This was for a tool and cutter collet holder, and fairly small
diameter.

As you go up, it gets harder. The thermal effects that would
never be seen on a 1.5" spindle start to get troublesome when
you get much larger.

No, weight and size are not the problem. There are telescopes
that use air bearings - RADIO telescopes! Many use fluid film
hydrostatic bearings with hydraulic oild, but there are some
with air bearings. A well-built air bearing, even of small
size, can have a radial stiffness of a million pounds/inch.
That means it takes a load of 1 million pounds to deflect an
inch, or 1000 Lbs to deflect .001" A large air bearing can be
quite a bit stiffer than that. This dwarfs the stiffness of
ball bearings, and even oil-film bearings need to be made with
insane tolerances to get this stiff. Of course, air bearings
like this ARE made with insane tolerances. And, there comes the
rub. So, you'd want to have a clearance per side of something
like .0002" to get really good stiffness. Making such a precise
fit on a 1.5" part is a challenge in the typical home shop, but
with enough time to lap the mating pieces you can get there.
Making a large lathe spindle and getting a reliable fit with no
barrel-bulges in the middle gets a bit tougher. Finally, unless
the bearing and the spindle are made of the same material,
thermal expansion may cause it to get loose or bind badly as the
room temperature changes.

How big a part do you want to turn?

Jon