Alan,

On Tue, 26 Sep 2006 13:27:51 +0100, Alan B. Pearce wrote:

> >Acme thread (different from square thread):
> > http://en.wikipedia.org/wiki/Acme_Thread_Form
> 
> Wow, that leads one into a whole cornucopia of info on threads. Thanks for
> the link.

Indeed - I'm beginning to wonder if I should quote my occupation as "Web Surfer!"  :-)

The Acme thread is the Volkwagen Beetle of the rotary-to-linear motion world, the Rolls-Royce is the Ballscrew.  Frighteningly expensive, they have 
incredibly low friction and a high pitch-angle - an inch per turn isn't unusual - and are very smooth and accurate.  They are also bi-directional 
(pushing the "nut" will turn the thread as well as the reverse) whereas an Acme thread isn't, which means that mounted vertically the nut would 
travel to the bottom unless the shaft is prevented from rotating.  

Excellent for CNC machine movements, complete overkill in the context of the problem we're discussing, but I though I'd add it in anyway!

Cheers,


Howard Winter
St.Albans, England


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