Re: [CAD_CAM_EDM_DRO] Best source for inexpensive ballscrews?

Yep, two standard ballnuts, one tightened against the other. That is
basically what the factory preloaded nuts do.

I like our design better because:

a) the thread pitch on the studs is finer than the factory "tightening"
thread pitch, making it easier to get the adjustment right. Truthfully,
we set the preload before installing the screws and haven't looked at
them since. Like I said, everything is tight backlash wise. We were
taking 0.020" deep cuts (on the radius, 0.040" on diameter) at f8, so I
think we are working them.

b) we can adjust the backlash on every axis without disassembling the
machine

c) they are less expensive.

The two drawbacks are:

a) it is a much bulkier setup, but also more robust

b) the studs have to be a tight fit in the holes or one ball nut will
rotate relative to the other, allowing the preload to be lost. This
isn't generally a problem, just be sure to use a DRO for aligning the
holes OR clamp and cross drill both at the same time.

BTW: we call the nut attached to the slide the load ballnut and the nut
that tightens up to it the backlash ballnut.

Also: many people don't realize this, but the backlash ballnut will be
subjected to the full load on the ballscrew in one direction of travel.
The backlash ballnut needs to take up more than a little slack as some
people think.

Kim

On Fri, 2003-08-01 at 19:42, Bill Kichman wrote:
> Wow, so you use (2) nuts per axis, and torque one against the other?
> Sounds like a good plan...
>
>
> R. William Kichman, P.E.
> Kichman Engineering Associates
> 103 Old Furnace Road
> Cornwall, PA 17016-0643
> tel/fax 717/270-0714
> ----- Original Message -----
> From: "Kim Lux" <lux@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Friday, August 01, 2003 9:29 PM
> Subject: 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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> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
> you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are there, for OT
> subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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> > List Mom
> > List Owner
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> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
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> List Mom
> List Owner
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--
Kim Lux <lux@...>