Re: [CAD_CAM_EDM_DRO] Best source for inexpensive ballscrews?

We just retrofitted a couple of machines for commercial use. We
purchased Nook ballscrews and nuts directly from Nook and from McMaster
Carr.

McMaster Carr sells Nook ballscrews and nuts for less than what Nook
sells them for.

There are two grades of ballscrews: rolled and ground. Rolled
ballscrews have an accuracy of 4 thou/foot. Ground ballscrews have an
accuracy of 1 thou per foot.

We too were turned off by the price and the size/mounting of the Nook
preloaded ballsnuts. We made our own preloaded ballnuts by mounting one
ballnut solid to table or slide and then mounting the other one to the
solid one via 2 fine threaded studs with aircraft nuts on them. This
allows one to tension one nut against the other nut. This setup has
worked very well although space is at premium because this setup is
physically large. Nevertheless we were able to implement this design on
5 of 5 axes between two machines.

This system has been in operation and testing for several days now.
We've checked backlash and positioning accuracy on our lathe for example
and found no backlash and virtually perfect positioning (0.0001") after
several hours of heavy duty machining.

Some preloaded nut designs rely on using a spring to hold the nuts
apart. I highly recommend avoiding these sorts of designs as the forces
generated by a decent servo motor on a ball screw are tremendous, ie a
thousand pounds or more.

In case anyone is interested, we used a pair of SKF 7203 bearings on the
motor end of the ballscrews to eliminate the endplay on the shaft
itself.

I also highly recommend direct driving the ballscrews. 3 of 5 axes we
did are direct drive; the other two are 1:1 belt drive. All axes have
more than enough force to machine at the power limit of the spindle all
day long. We only used the belt drives where space limitations required
us to do so. During quick rapid machining moves one can see the belt
vibrate and dance. We also dislike the size of the belt pulleys (ie
their thickness) and their cost.

Our machines have axis speeds of 150 inches per minute, limited by the
step generation rate of the software we use.

Ballscrews may seem expensive at the time of purchase but they
dramatically improve the performance of the machine. In a long run they
are a bargain. I highly, highly recommend them.

Kim Lux

On Fri, 2003-08-01 at 19:00, Bill Kichman 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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Kim Lux <lux@...>