Re: [CAD_CAM_EDM_DRO] Re: Best source for inexpensive ballscrews?

Coupling the ball screw takes more than just grinding it down. One our
retrofits we use a press fit spindle. The spindle is 7 inches long
overall. It has a bore 3" deep that press fits onto the ballscrew. It
has a step 17mm x 1.5 inches long for 2 angular contact bearings, a
threaded step 0.75" long x 5/8" thread for a threaded collar to preload
the bearings, and a step 0.5" x 0.75" long to couple with the motor.

The angular contact bearings and the threaded preload are essential to
attaining a true zero backlash system. We use SKF 7203 bearings.
McMaster Carr also has these.

BTW: 3/4" Nook ballscrews do NOT have an OD of 0.750". They have an OD
of roughly 0.717 inches. There is no need to anneal the ballscrews to
machine them. A slow feedrate and a good carbide insert tool will cut
them. We did not weld the ballscrew to the spindle, just pressed it
in. One could further hold it with a setscrew if desired.

We left the ballscrews as big as possible in order to retain as much
strength as possible. We machined the bore in the spindles to the
biggest drill size that was smaller than the spindle OD and then turned
the minimum off the ballscrew necessary to achieve a press fit.

If one ground/turned a 3/4" ballscrew down to a solid core, it would be
less than 1/2" diameter and fitting a stepped arrangement of bearings,
preloading collar and drive stub shaft would be nearly impossible.

Now that we CNC these spindles, we would be willing to make some for
people who want them.

The locking threaded collars are the key to the whole assembly. We used
McMaster Carr part number 6438k24 on page 1000 of Catalog 108. (or see
their website.)

I share this information because we spent a lot of time figuring out how
to make this all work and I've gotten a lot of information off this
mailing list.

On Sat, 2003-08-02 at 04:33, kdntool wrote:
> Bill,
> When you come to the point of how to couple to the end of the
> ballscrew, look for a local "mom and pop" centerless grinding house.
> The local shop near me has a reasonable min. charge and was more than
> willing to grind 2.5 inches of each end of the three ballscrews I
> brought to them for the min. charge. Don't mess around trying to
> anneal the end and turn, press, or weld. If you can't find a local
> shop, contact me off list and we will discuss sending me the screws
> and I will have them done for you.
> Regards,
> Ken Cardolino
> KDN Tool
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bill Kichman"
> <billkichman@c...> wrote:
> > Just curious what others have done in the way of obtaining cost
> effective
> > ballscrews for their conversions. I am doing a full sized mill
> conversion,
> > and simply cannot see spending $1k to $3k for a set of preload style
> > ballscrews for a hobby venture. What is the least costly solution?
> > Thanks
> >
> > R. William Kichman, P.E.
> > Kichman Engineering Associates
> > 103 Old Furnace Road
> > Cornwall, PA 17016-0643
> > tel/fax 717/270-0714
>
>
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