If Dean built it then machine will be OK. No harm trying the air cut without spindle running to be sure. Please try that by moving the spindle off to one side away from the part, zero the x and y and run the code ( if using M commands to start the spindle in the code this will have to be commented out or you may be able to run without the VFD switched on).

If this runs fine then you have some interference.

If this has the same problem then read on.

As this happens on 3D jobs then I’m leaning towards the gcode or software setup. Is there a short bit of code you can post here and we can see if there are calls for z height changes in odd places. Or more likely perhaps there is something in the settings. Unlikely but perhaps the Z acceleration is high, so note the value now and try lower accels on Z. Also try lower feed rates using feedrate override.

Just trying to get some more clues really and hopefully Dean will be along shortly as I’m sure it would already have safe settings so we can get past that part.