I am not completely sure as to what your problem is, but the followingassumes that you are milling PCBs. But perhaps you are talking aboutgeneral milling instead. In that case parts of this will beapplicable.
There are commercial devices available for setting the Z axis zero. Theyare usually electric or electronic and they depend on the tool beinggrounded through the machine so you need a ground connection. They areinsulated on the bottom side and have a conductive top so they can beused on all materials. Some give a visual indication and others areelectronic and can be connected to the computer so the software can dothe touch off itself. The commercial ones will have a known spec fortheir thickness and you can measure them with a caliper or micrometer toconfirm this. Of course, you can also do a test piece and check theresults, making further adjustments in the effective height as needed.Things like ball bearings (in the machine spindle) are not designed to begood conductors so, depending on your mill, you may have to add a groundclip to the tool itself. Frankly, I would do this as a matter of course.
If great accuracy is not required (as in milling a PCB), you can make asimple such device with a small piece of copper clad board. Attach a wireto the copper at one corner and run it to the computer using whateverinput your software allows. A pull-up resistor would be needed on thatline. When the tool hits the copper, the copper becomes grounded and thesoftware would detect that. You would measure the thickness of this homebrew Z pad with calipers or micrometer and enter it in the software tocompensate it for that.
If you are milling PCBs and trying to compensate for any angle that thePCB may be sitting at due to warpage or whatever, your software wouldhave to be able to compensate for that. You would simply use that featurein your software and take several Z readings, probably at the fourcorners. If the software does not have this compensation built in, thenit would be very difficult to edit the G code to add this compensation.For this you need to read the documentation.
If you are milling BCBs, I would suggest that it is easier to make betterclamps to hold the PCB flat against the mill's table which should beflat. Two, full length edge clamps should hold the PCB reasonably flat.This would avoid the problem of warpage and only a single touch off pointand no compensation would be needed.
Posted by:
Hello and good day all. My name is Silas, and I am trying to
figure out how to get the correct Z axis compensation for
non-conductive surfaces.
I have successfully set-up a touch off system on my Zen-works 7x7
mill using Linux CNC and autoleveller, which is an awesome piece
of software btw.
I can easily use it with copper clad or any other conductive
surface, however the documentation is too brief on the touch off
plate method. I can easily have the autoleveller code touch off
using a piece of copper clad and moving it around the
non-conductive object to get level readings. My question is how
do you go about compensating the height of the material used as
the touch off plate throughout the entire GCODE file?
Any help on this matter would be greatly appreciated.
Thanks,
SIlas.