Re: [CAD_CAM_EDM_DRO] Rolled vs. Ground ballscrews

hi. i had a rather long chat with cliff taig on just
this topic.
here is the sense i made of it all:
1 - there can be no tighter bearing than flat metal to
metal
2- as soon as you introduce additional elements, like
rollers, you are dealing with multiplied tolerances of
all the parts (read as ERRORS of all the parts)
3- ball screws/nuts immediately reduce native
resolution cuz they can not have as many tpi as a fine
thread screw.
4- they are expensive, sound hella sexy in a
specsmanship pissing contest.

in other words, what has been conveyed to my mind is
that they are not really worth having even if got for
free!

on principles, ballscrews can never be as good as a
good screw.

--- Dan Mauch <dmauch@...> wrote:

> I installed some Thompson rolleed ball screws (.003
> tolerance) on a mill
> drill. I used two ballnuts and preloaded them so
> there is about .0005
> backlash on the X axis. I then proceeded to check
> the accuracy by using a
> long drift dial indicator and resetting it. The
> .0005 backlash was taken out
> before the X axis was moved in the + direction
> The results were surpising
> x =0 on manual dial dial indicator 0
> x1.000 x.998
> x2.000 x2.000
> x3 x2.997
> x4 x.3.999
> x5.000 x.5.0
> You decide it it meets your needs
> Dan
>
> ----- Original Message -----
> From: "Jim Colley" <jcolley@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Sunday, September 18, 2005 3:25 PM
> Subject: [CAD_CAM_EDM_DRO] Rolled vs. Ground
> ballscrews
>
>
> > Alright guys, maybe some of you are open to a
> little debate.
> >
> > I am in the design phase (still) of a 5-axis mill
> and have purchased
> > nearly all of the pricy stuff except ballscrews.
> Now, obviously
> > ground ballscrews are more expensive due to their
> higher accuracy,
> > etc.
> >
> > My question is, exactly what are you getting for
> your money and is it
> > posssible to achieve the same end goal using
> rolled screws and a
> > little clever design?
> >
> > If the major difference is the accuracy of the
> lead and backlash,
> > then wouldn't it be possible to eliminate the
> backlash in a rolled
> > screw either by using a double nut design
> (preferred) or repacking
> > the ball nut with larger diameter balls? Then,
> once the backlash is
> > minimized, the only real concern is the accuracy
> of the lead.
> >
> > Now, my thoughts here are that this is only a
> concern if you are
> > using the servo motor's encoder to close the
> feedback loop by
> > interpolating the axis position from the number of
> rotations and the
> > diameter of the screw. However, if you used linear
> encoders on the
> > axis (preferred) or used an arrangement with a
> timing belt fixed to
> > the slide, turning a pulley which drives a rotary
> encoder, wouldn't
> > that give a very precise readout of *actual* axis
> location? Provided
> > there is *no* backlash in the ballscrew
> arrangement, there should be
> > no problem with hunting on the servo mechanism,
> etc.
> >
> > As I have said before, I base my statements on
> absolutely zero
> > experience and no intelligent thought whatsoever.
> Just an idea
> > I had.
> >
> > What do you guys think? Any problems? Better ways?
> >
> > Jim
> >
> >
> >
> >
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>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
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> 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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