Shopbot lost steps during cut

[phil_o]

Yesterday I was cutting out a new 3D file, a round plate, 10" dia, mahogany. About 20 minutes into the cut which was around 2/3 of the total cut time I heard a grinding noise, I was close enough to the machine to stop it right away. The machine had lost the X-axis by about 2" (I hope that explanation is clear).
I thought that maybe the bit had slipped but it had not. This was a finishing cut with a .25" ballnose but, moderate feed rate, 14 K spindle speed.
I've had this machine for over 10 years, I have a lot of experience with it but it has not been run hard.
I finished the cut by zeroing X Y and Z and edited the file to start at the opposite side of the material.I ran it past the point where the problem had occurred and it was fine.
Any ideas on what might have caused the grinding and loss of X zero?

Phil

[letterman7]

Mine does that quite a bit. I think it's a combination of stuff in the threads of the rack, the carriage being not quite square (check to see that all your v-rollers are actually on the rails) and in my case(s), simple static and an old computer throwing random errors.

[srwtlc]

Are these standard or alpha machines? Too aggressive speeds and ramping can cause a standard to lose steps while rastering back/forth up/down on 3D files.

[scottp55]

Static season IS starting....I lost position last week for the first time in ages...turned out my bare wire ground where it came out of hose and was spliced to go around a blast gate had separated. Hasn't repeated since.
Last year it was corrosion at the dust deputy steel canister on a screw:(
Maybe check grounds?
scott

[phil_o]

I contacted tech support, they had a list of items to check. One of them is a USB speed test that is a diagnostic tool that is part of the SB software. The USB port I normally use tested at 56%, 75% is the target number. One of the three available USB ports test at 80%. I haven't run a cut file since but it should make a difference.
Thank you to SB tech support.

Phil