Andy,

That is what I'm making too.  A rotating ball nut.   I looked at all the
ways there are to lift the head of a Siege X2 mini mill and I think the
question comes down to the location of the screw.  I think I will use the
space occupied by the factory installed column mounted rack.   The screw
will be fixed to the head and lifted straight up by the rotating ball nut
I'm using a 16mm dil x 2mm pitch screw.    All other designs place a
twisting force on the Z-axis dovetail

This belt will connect to a nut that looks like yours.    But I read the
belt literature and far and away the GT2 profiles seems best.   They are
now calling it GT3 and say it interchanges with GT2 parts  The belt teeth
are little semi circles.


My question was about pitch.  Should the belt pitch be 2mm, 3mm or 5mm.

So I look up technical data for the belts and each pitch has a minimum size
pulley and different maximum RPMs.   Using 3mm pitch allows the motor to
spin up to 5,000 RPM.     I doubt I will run the stepper motor that fast

On Thu, Feb 22, 2018 at 3:30 AM, andy pugh <bodge...@gmail.com> wrote:

> On 19 February 2018 at 09:08, Marcus Bowman
> <marcus.bow...@visible.eclipse.co.uk> wrote:
>
> > I am planning to renew my belts after some 13 years fairly heavy use
> (ballscrews now worn), so I too have been pondering this problem.
> > The SDP/SI site at http://www.sdp-si.com/products/details/timing-belt-
> detail.php#gt2
>
> I have always used the metric "T" profile belts, also listed on the link
> above.
>
> I don't know if they are technically suprior or inferior to other
> systems, but they are readily available (from RS and other UK
> supliers) and I have a pully hob so can make my own pulleys.
>
> Here is a rather special one I made for a rotating ball-nut
> arrangement. (that's the ball nut in the middle).
> https://photos.app.goo.gl/1dJiuUVVdZmrghI93
> It was for the X axis of my mill, which is why the hob feed rate was
> uneven and too fast.
>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1916
>
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-- 

Chris Albertson
Redondo Beach, California
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