Problem With program

I am having problem with a gcode program I am using. I am cutting out 4 pockets. I made it using Fusion 360. All of a sudden - at a random place in the program the z-axis starts plunging down at a slow rate until it crashes through the bottom of my part and in to the spoil board. I have run the program more than once and it seems to happen at a random place in the program. Once during the first pass during the first pocket, once during the second pocket. I ran the program once with no wood (dry run) and it worked as expected. This tells me is not the gcode but something with the machine. Can anyone help? I am happy to provide any information that may be useful to anyone here. This is my first experience with a Shapeoko although I did CNC work for a number of years a while back… I am at a loss and really discouraged. I also ran the .nc file through a simulator (outside and inside of F360) and it all seems as expected.

Are you certain that you have set the correct sort of Z-axis?

Could it be a mechanical problem such as the endmill getting pulled out of the collet? Or the machine getting pulled into the cut due to high tooling engagement?

Sounds like (99.99%) that you are pushing the machine too hard ad are missing steps. Depending on what Z drive you have it can be the weak-link here.

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I have a Shapeoko 4 XL if that helps. I am cutting walnut with a quarter inch end mill at quarter inch depth of cut at 24ipm.

It also happened once with mdf.

Since it didn’t do it with the test cut…it’s the Z. I hope it’s a single or two flute cutter. You stated 24 ipm…Z feed rate?

Now that you mention it it when I notice this happening I turn the machine off immediately. Both times the end mill has come out when I home it afterwards. This is perhaps a big oops on my part. Not tightening the end mill enough or perhaps I am going too fast? Or too aggressive on the depth?

2 flute end mill 18K Rpm

Sorry - 24ipm on x/y. Z is 13 but it is happening during the pocket portion - not during plunge.

Is this too aggressive in anyone’s experience? I am beginning to think I have under tightened my collet. And my endmill is coming lose.

The numbers (Z) look ok…but I still think it’s the Z (missing steps). Try changing the Z to 5 for testing.

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Thanks for the super fast feedback everyone. It’s communities like this that make these things so awesome. I will report back my findings so that there is resolution for any future readers.