@Reinard St.
Thanks for the welcome, it feels like I have made contact with the forum.
Good tip about the WinPC-USB to save it in a new configuration. I will follow up on that.
Same for the handwheel and that has a priority!
I noticed during my engraving test runs on marble that it is extremely important to:
a) have your surface *absolutely* level.
b) have an correct measurement on Z for that surface.
A short recap on my tests.
I tried to clamp down a marble tile (of 100 x 100 x 10 mm) and I thought it was level.
It was level within the measurement uncertenties of positioning/probing the four corners with the screen positioning tool, which is someting arount +/-0.2 mm?
Running my gcode for the engraving (at a depth of 0.1mm) the left side was not scratched at all and the right side showed some traces.
Thinking about it, the clamping might have bend the working surface of the 420 (I was not using any extra safety layer under the tile, no danger of drilling through) The tile was in the middle of the x-as and right at the front of the y-as. If bending is possible, this would be just the weak spot.
Next run I tried with a depth of 0.2 mm and I got an result. But it was more 'milling a trench' than 'engraving a line'.
If bending the bed by clamping force is in play then I have to come up with a method of checking and correcting it.
Doing probe measurements with the current screen controls is not accurate enough.
But keeping the z-ax fixed at Z and move to the four corners I can easely measure the height of the spindle holder above the working area within 0.01mm
Tightening or loosing up the clamp down bolts can than be used to level the surface.
That is what I want to try on my next run, which will be somewhere beginning next week.
This clamping down works with the marble tiles I have (left overs from a bathroom redecoration).
It will be interesting to see how this will work on glass.
In both cases, marble and glass, leveling the surface with a milling action before the engraving is not possible I think.
If everyting fails and I cannot come up with new ideas I will start asking questions in this forum.
Always good to know that some other people have already done/archieved what I want (which proves that it is possile) and are willing to share their experience. But the best way to learn is for myself putting one and one together and see if it works.
Kind regards,