Re: Geckos, Servos, VFD and twitching on Z axis

The Z servo is only about 8" from the VFD and 12" or so from the
spindle motor. We are moving the quill, this is how the machine was
originally set up back in 1985. I'd rather move the quill than the
table with the servo, less weight. Machine frame is quite rigid. The
drifting is random. .001 one cycle then .005 and sometimes as much
as .030 another. The direction will be random also.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Raymond Heckert" <jnr@a...>
wrote:

> How close to the Z-axis controller to the VFD? Maybe the
> electrical 'noise' is causing problems. Are you using the
> quill as the Z, or are you raising & lowering the table to
> effect a Z-move? Is your ram rigid enough to prevent it's
> movement under power? Does the 'drifting repeat itself
> with any kind of regularity, under load? These are all
> things I'd take into consideration in troubleshooting.
>
> RayHex
>
> ----------
> > From: yethdear0 <da-mack@e...>
> >
> >
> > Hiya,
> >
> > We have an old Hurco knee mill that we have stripped and
> retro-ed
> > with a pc, CNCPro, Geckos and a Baldor VFD for the
> spindle motor. We
> > just got it all up and running but have a problem with
> the Z axis
> > servo or controller. Using a travel indicator on the Z
> axis, the
> > movement is smooth and exact. We have the machine running
> a program
> > that move Z -.100" pauses for 1 second and then moves Z
> +.100" and
> > then runs in a loop. When we turn on the VFD and the
> spindle, the Z
> > axis seems noisy and the travel on the indicator will
> start to
> > drift .001" to .005" each time the program cycles. The
> drift is
> > random, sometimes positive and sometimes negative but
> positive the
> > majority of the time. When we slowed the motion to 1 ipm,
> you can
> > see the motion twitch at random during the movement. This
> only
> > happens when the spindle is running and only the on the Z
> axis. We
> <snip>