Very bizarre Z issues

CNC Machines Shapeoko 3
1

Not sure what is happening here.

I run one file using a profile cut and a 1/8 bit, and have no issues. I can complete the whole file, and the z height maintains proper height and everything cuts okay.

I switch to another file, with a vcarve cut, and while it starts out okay, it’ll eventually raise itself a good few mm above the workspace. Extremely hard to explain, so i took a video. Couldnt figure out how to upload here, so I uploaded to a video hosting site: IMG_6085

It always happens about the same location on the work surface. I’ve recreated the design and the toolpaths in new files. I am using vcarve 9. I’ve tried different bits. The collet is tight, the router is clean. The router doesn’t hit anything. The wood is flat and straight and clamped down evenly. I’ll end the cut, reboot everything, and try again and without fail it happens again the exact same way. Over and over again.

I’ve dealt with a LOT of gremlins with my 3XXL, but this one takes the cake. I am so lost and have no idea how to fix it. Nothing i’ve tried works.

HELP.

2

With a belt-drive Z-axis one has to be very careful of depth per pass — if you push this past the belt’s ability to hold position it will result in lost steps — or, it could be that the belt isn’t sufficiently taut.

3

With a belt-drive Z-axis one has to be very careful of depth per pass — if you push this past the belt’s ability to hold position it will result in lost steps — or, it could be that the belt isn’t sufficiently taut.

I should have mentioned that I replaced the z belt already a couple of weeks ago, so its brand new. Everything is tight, belts are tight, vwheels are replaced and secure.

I don’t have a flat depth set, but i’ve run this file for the last 3-4 years without having issues with the current settings and toolpaths…

Bit is a 0.50 wide 90V using default settings of 0.25 pass depth, 0.01 final pass stepover. 16K RPM, 100ipm feed, 30 ipm plunge.