Re: [CAD_CAM_EDM_DRO] Re: making ball nuts

> Suppose, however, that arch threads are a sine qua non. As Jon points
> out, grinding the gothic arch shape with a form wheel on a long
> spindle tool grinder definitely is not a machine shop 1A project. Now
> shaping a toolbit to the arch shape shouldn't be too bad, especially
> not for someone with a fine touch (I'm not claiming to have one), an
> optical comparitor, and actual knowledge of the required shape. It
> might be necessary to vivisect a donor nut to figure out the thread
> profile, plus a lot of time with measuring wires and recollection of
> trig identities.

Okay, silly (I mean really silly) idea time:

Why does the internal thread race form need to be arch-like at all?
Why can't it be a V? That would mean a single point of contact with
the thread race - shure it might wear, but if the nut were cheap and
the balls were too...

So - how about buying (or making) a large diameter coupler nut with a
standard 60 degree V thread form. Harden and lap it in on a piece of
threaded rod. Add return channels and fill with an appropriate size
ball. I don't know that there is an off the shelf nut and ball size
that would work out to matching any of the standard rolled screws -
but if you made the nut yourself it should work.

I think the key aspects here would be:

1) lapping the threads on a screw to increase their consistency

2) using the nuts in preloaded pairs, so the balls only contact on one
side of the thread race.

Chris

(Okay - realistically - some of the ballscrew sizes are a lot cheaper
than others without respect to dimensions. The best practical way to
save money seems to be to design your project around the cheapest size
that is big enough to be strong but small enough to fit. 5/8" and 1"
both seem quite reasonably priced)

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
(617) 629-9830 home (temporary), 253-2606 MIT