Unusual behavior by machine

[SAA3840]

Today I had the most unusual thing happen with my machine. I was carving a sign, .mpc attached, when the machine quit carving the lettering on the sign. The Y/Z trucks quit moving but the bit, a 60 degree "V" bit kept spinning about 1/4" above the board. The X drive kept moving the board VERY slowly forward until I stopped it when the edge was about 1/2" past the bit. I tried stopping and restarting the machine several times but the carving never resumed. I ended up stopping the project, editing the .mpc, deleting everything that was already carved and restarting the project. The machine re-measured the board and started carving, apparently exactly where it left off. I can't tell for sure yet as the "recarved" portion is hidden right now. I'll know for sure tomorrow when I restart it.
Any ideas what went on?
Grandma's Babysitting is the original .mpc and
Grandma's Fix is just that, the fix to recarve.

[bergerud]

That kind of behavior makes me think that the brass roller may have been interfered with by the front belt. Check to see if the belt and brass roller are close when you push the brass roller down. If you have sandpaper belts, it may be rolled under. If you have rubber belts it may be too close.

(I am thinking that once the brass roller was interfered with, the x drive tries to readjust to agree with the new position. As it tries to catch up, the brass roller keeps rolling ahead of it and you end up with a slow race to the end of the board.)

[Digitalwoodshop]

To address the bit hovering above the board.... Likely a Z Problem... Dirty Rails, dirty Z Encoder, Bad FFC Cable....