re:making ball nuts

Jack wrote:

>These things are so !@#$%^! expensive; has anyone ever made their
>own. Isn't it 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?

If you're a good enough machinist to contemplate this, you can
probably pull it off. But, the devil IS in the details... and It
seems you will easily spend more TIME to create something which is
readily available at what you will probably LATER decide is a "fair"
price.

>Isn't it 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?

Most Ball races use a "gothic arch" shape rather than half-round in
an attempt to keep the balls rolling, (rather than sliding) and also
to deal with the deformation caused by loading. Most mfr's catalogs
show the "what and why" of this.

>I don't yet fully understand all the details of ball recirculation,
>but it looks like drilling some holes and silver soldering some
>tubes.

This is sort of like "porting" a head on an automotive engine.
Also "just" a couple of holes drilled... :-)

Again, the goal is to keep the balls rollin', not sliding or
sticking. A "transition" exit/entrance curve is necessary. For a one
of, you could probably do this with a die grinder.

> Preloading means making two of 'em and sourcing a spring, right.

Yes. Belleville washers are commonly used. Or... You can load
slightly larger balls into the nut to create pre-load. You'll need to
do this set of engineering calcs yourself.

>So, group, what obvious factor am I missing?

Besides what I already mentioned? Precision. Hardening. Grinding.

Obviously you CAN make these yourself. The people who make them ARE
making them themselves, right!

I think there are enough other areas in CNC where MY efforts are
better spent, so unless I'm just lookin' for some learnin', I'll buy
the ballnuts. As more people have gotten into motion control, the
prices of basic ballnuts has come from ridiculous to realistic,IMO.

Where you MAY realise some savings is in creating a "preload" nut
from two "cheap" plain Ballnuts. Or by using the above-mentioned
larger balls in one (purchased) nut. Wouldn't it be great to find
that we could buy a $30 nut and "re-load" it for anti-backlash! If
you pursue this, be sure to let us all know whatcha find out?

Hope this helps.

Ballendo