Help needed! Machine crashes on 3d milling

I believe your Z axis is losing steps, or maybe a shaft coupler is slipping.
Check the shaft coupler to make sure 1 of the screws is firmly against the flat on the shaft so it cannot slip.

If it is losing steps you may have heard a 'strange noise' during a retract move. In this case you need to do 1 or more of
- increase the current to the Z stepper motor (if it gets too hot to touch that is too much!)
- decrease the Z max rate and Z acceleration settings. (especially in light of your 4000mm/minute feedrate), decrease acceleration by 25% and test, if that fails then reduce by another 25%, and so on.

Also, please use the OpenBuilds Fusion 360 postprocessor if your controller is GRBL based.
docs:software:fusion360 [OpenBuilds Documentation]
Your Gcode is doing some odd moves, like at the start
G0 Z15
Z-4.77
which means it rapid moves 4mm into the wood. This kind of rapid cut can easily cause missed steps though in this case it would make the Z 'too high' on later cuts. (EDIT: this move makes sense after the adaptive clearing roughing cut, ok)

I would like to see your Fusion360 file to get a closer look at how you have set up this CAM.

 

Does it do this in the same place every time?

 

Thankyou

I was right, that -4mm Z plunge on the finishing is a problem because the roughing did not cut the shape out to the edge, only to the inside of the bottom flat portion of the model.

You can see the tool is red in the simulation, this means it is 'crashing' the tool into the material during a rapid move.

To solve this the roughing geometry must be selected as the outside of the model. A refinement to make the finishing pass easier is to add an offset so it cuts slightly outside the outline.

The green line is the selected geometry so it roughs all of the bowl shape.
Then you can see 2mm in the 'additional offset' box, the label is obscured by the hint text just under 'Tool containment'

I also changed some other settings, reduced the ;layer height a little so that the final cut is a real cut not a scrape. Increased the non cutting feedrate, reduced the heights so it does not retract so far which is just a waste of time. changed the minimum stepdowns too, no need to be as fine as 0.5mm. I also changed the 'stay down' parameters so it stays down instead of lifting up all the time, this saves a lot of cutting time. now a 46 minute cut instead of 1H30:00 or so.

passes tab


linking tab


So now the end of the roughing looks like this with cuts that actually overlap the outside of the bowl so the finishing pass can cut right to the edge easily.


The finishing toolpath does not need multiple depths, the roughing is leaving 0.5 to 1mm for it to cut, so I turned that off.


so the finishing looks like this

and does not generate any collisions in the simulation and is now down to 31 minutes cut time.

you can see that the finishing (bright green) does not cut as far as the roughing cut because of the additional 2mm offset, this makes for smooth entry and exit at each end of the passes.
If cutting a hardwood I would even increase the offset more to give more space for the finishing.