Wow - this is the best explaination I ever saw. Now it is clear to me.
The machine zero point is defined with the limit switches and it is the highest z value. I thought it is always lower z value or the work area z point.
Now it is clear why the Z-15 was sent.
I appreciate that - thank you very much Haldor.
And Neil you are right. I used the standard GRBL that came with Fusion and this is working now for me.
With a small issue. So the fact that my China cheese mill does not have limit switches, I move the tool to the material work area zero and set all axis to zero inclusive G28.1 by hand. If I start the generated fusion g-code, it is moving the xy position to the start point for the first milling - without moving the tool. So I have to add manually G0 Z2 to lift the tool for 2 mm and start the xy movement afterwards. I do not know if I can customize this ülifting automaticly, because this is in the preprocessors section of the to be milled bag.
For the second bag in the sequence, the tool is lifted. This is switched on in the fusion setup for fast positioning (lift tool 2mm). Not sure why this is not working for the first section in the setup.
But thank you all for helping here. Now I can work with the mill…