Why Is my X-Carve taking a nosedive into the table?

I am stumped. can anyone help? I am having a problem with my final pass, about halfway through the cut, my bit takes a nose dive into the table. it keeps getting gradually deeper as the cut goes on. I have replaced the z axis belt, made sure the pulleys are tight, even ground a flat spot on the stepper shaft so I know the pulleys are not slipping. I have mad sure the delrin nut is clean and moving freely on the screw. I have checked my Gcode for errors.

it looks like it is trying to go up and slipping or skipping teeth on the belt then the Gcode tells it to return to the cutting position and making it go deeper. if that is happening over and over, that would cause this, but I am unable to fix the issue with the troubleshooting above.

Picture 1 - Latest cut, 3rd run
Picture 2 - What it should look like
Picture 3 - when the problem started, 1st run
Picture 4 - Caught it before it went into the table, 2nd run
Picture 5 - 7 - Latest run still on the table

Am I missing something? Thanks for the community, you are all great.

Check set screw on Z axis pulley.

This prob wont help, but i had similar issue when the router bit was not tight in the collet. Didnt make sense to me why the router was plunging deeper when bit was not tight.

Based on what I’m seeing there with a progressive loss in Z height, its most likely one of 2 reasons:
1. Your bit is not installed properly resulting in it coming loose in the collet and the bit itself dropping down slowly. By chance, was the bit fully seated to the top when installed?

2. you got chips in the Z axis movable parts (most likely stuck on top of the V Wheels forming like Wheel Chocks for a car and allowing it to move up a bit but not enough resulting in a loss of steps in the stepper)

Although much less likely:
the Z pulley couplers could be loose (tighten the set screws 3 per pulley)
or the tension on that belt is not set properly and that may need adjusted,
and finally, and this one would require the operator input to edit the grbl settings AND would really only come into play if you have Z lifts between each pass however; IF the z max speed was set excessively high it could cause a loss of steps during the retract portion and it would result in a progressive lowering like this…

If any clarification is needed, tag me and I’ll go into depth further… :+1: