Re: Grizzly G8689 mini-mill CNC retrofit kit

--- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:

>

,

>
> Do you literally mean GEARED servo motors as in with gears instead

of timing belts or something? How much backlash is in the gear
train, and how well does the servo loop deal with it?

>
> Chris Stratton

Chris,
Sure do. Backlash isn't a significant factor. Molding techniques and
materials are so good that now even cheap gear trains (and these
aren't) don't have detectable backlash. Throw in ball bearings and a
good design and its mostly gone. As far as the servos are concerned
as long as the encoder is on the motor and not on the gear train
there isn't much difference between this arangement and the slop in
the timing belt. From a system standpoint it looks like backlash and
CNCPro does backlash compensation. For the Grizzly I seen to recall
the x (worst) axis was about .003".

I would agreee that this is sloppy if you are comparing this setup to
a encoder mounted on a pre-loaded ballnut / ballscrew stretched
between preloaded abec 7 bearings. Best case the motor drives the
leadscrew though a belt. Because the encoder is on the leadscrew even
belt play doesn't matter. My Tree mill has almost no detectable
backlash but it cost about $40,000 in 1985 and weighs in at 6,000
lbs :). Not a fair comparison to a Grizzley.

Roger