Re: [CAD_CAM_EDM_DRO] Bridgeport Interact II not 0

I've been running my Bridgeport Interact II with Geckos and Mach 3 for a couple years.  Thot I had it pretty "dialed in" - motor tuning set very close to 20000. Yesterday I started a job that drilled a hole at 0,0, moved and drilled holes at (+/-X,0) and (0,+/-Y) then returned to 0,0 to start another part of the job.  Even though MACH says I'm back at 0,0,0, the tool was visually off.  I recentered and it appears to have been off at least in X by 0.033", Y.. maybe 0.005 ish. After recentering (visually) I cut a circle, which cut within about 0.001" dia, and that's with no backlash compensation in MACH.

Need help understanding this... 

Missing steps? - rapids were only like 15 ipm, "sounded good" while moving, I was VERY surprised to literally see it noticeably off center.

Backlash? - seems good based on the circle I cut

.033" seems way too much to be backlash.  I'm not a Mach user, but any possibility you hit a wrong key and changed the coordinate offsets or coordinate system by accident?  I've had a few crazy things happen with LinuxCNC, and I'm pretty sure a few of them were "operator error".  If you do it just right, these can cause small offsets that won't be instantly obvious.  Some other crazy stuff turned out to be a bad connector that had my motion interface running on 4 V, when it was supposed to have 5.  Took a while to even realize something was actually wrong, then took some time to locate the bad connector.  It could be a bad connection that comes and goes, possibly as the machine moves.  Those can be VERY difficult to track down.

Jon