On Mon, 21 Feb 2011 10:23:58 -0600, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

"Pete C." fired this volley in news:4d62907a$0$1855
:

For a servo
connection you need to use a "hard" connection. Note that in a manual
mill, the feedback from the dial or from a scale is after the handle
clutch and thus the handle clutch backlash is not a factor.


So long as you mean "tight", not "hard" I agree.

A lot of stepper-drive machines use a Lovejoy coupling between motor and
ball screw, with a very tight (even very tightly compressed) spider.

Unlike steppers, servo tuning is compromised by lack of angular
stiifness in the loop. Lovejoy couplings are quite soft in that
regard, and I think that's the sense Pete was using when recommending
a "hard" coupling. Oldham couplings are often a good compromise when
highest performance is not required.

--
Ned Simmons