Re: [CAD_CAM_EDM_DRO] making ball nuts

jmw@... wrote:

> These things are so !@#$%^! expensive; has anyone ever made their
> own. Isn't just a matter of cutting an internal thread with a half-
> round form tool, e.g. a round carbide insert or hardened piece of
> drill rod?
>
> I don't yet fully understand all the details of ball recirculation,
> but it looks like drilling some holes and silver soldering some
> tubes. Preloading means making two of 'em and sourcing a spring,
> right.
>
> So, group, what obvious factor am I missing?

The inside of the ball track needs to be ground to a precise form.
Since
you will use external preloading, the precision isn't so tight, but you
still
need a pretty precise shape and diameter. So, you need to make a
tiny grinding wheel with a sculptured shape (in cross section), mount
it on a rather small, long arbor, mount the arbor on a tilt equal to the

pitch angle of the thread, and then grind the thread on the interior of
the nut. Form tools could be used first to rough the thread to near
final
diameter.

I've been thinking about doing this, but it is DEFINITELY not for the
novice!
Actually, the shape used is usually something like an arched church
window
with a point at the top. This prevents the ball from being loaded
directly
radially, between the nut and screw, where it will do no useful work.
You want the balls to ride somewhat to the side of the tracks, and carry

the load more axially.

Jon