On Tue, 16 Aug 2011 11:21:27 -0500, "Pete C."
wrote:


Ned Simmons wrote:

On Tue, 16 Aug 2011 07:36:23 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

I'm doing a cnc conversion on a 13x40 gearhead lathe.

My Z servo will be belt driven, so I think I can handle that.

Do any of you have a recommendation for a zero backlash coupling for the X
drive, which will be direct?

(metric AC servos)

LLoyd

I like Oldham couplings for this sort of thing. They're much cheaper
than higher performance options like bellows couplings, less fragile
and cheaper than helical beam couplings, and usually good enough in
all but the most demanding motion control apps. McMaster has a limited
selection; Lovejoy and Huco have much more. Lovejoy has some
comparison info in their catalog.

http://www.lovejoy-inc.com/products/...couplings.aspx

Those are not zero backlash couplers. McMaster has zero backlash
flexible couplers specifically intended for servo use. They aren't
particularly cheap, but if you only need one of them they should be
acceptable.

The Oldham couplings from Huco and Lovejoy are zero backlash, as are
those that McMaster stocks. There's a light interference fit between
the aluminum hubs and the delrin discs. The disc is much stiffer
torsionally than the elastomer spider in typical jaw couplings, which
also suffer from backlash. Oldhams are stiffer and have lower inertia
than a helical beam of similar torque rating. And if you bust one,
replacement discs are a couple dollars -- cheap enough to keep a
couple spares on hand.

In highly dynamic systems a disc or bellows coupling may be necessary,
but I've used Oldhams in many less demaninding apps with no problems.

--
Ned Simmons