Depends on how you measure z reference. If you have bed as Z=0 and use a probe to test surface as 0 you use G30:
- G30 P<0..3> - Single z-probe at current position P = 1 first measurement, P = 2 Last measurement P = 0 or 3 first and last measurement
- G30 H<height> R<offset> Make probe define new Z and z offset (R) at trigger point assuming z-probe measured an object of H height.
The second use case is what you want. Having no mill in use I always forget the sign, but the idea is to tell object is xmm height and you want an offset of x so top is 0. That will use internally G92 to set an offset so negative Z is still allowed.
An other solution is disable target position checking with G1 S1.
Comments
- G30 P<0..3> - Single z-probe at current position P = 1 first measurement, P = 2 Last measurement P = 0 or 3 first and last measurement
- G30 H<height> R<offset> Make probe define new Z and z offset (R) at trigger point assuming z-probe measured an object of H height.
The second use case is what you want. Having no mill in use I always forget the sign, but the idea is to tell object is xmm height and you want an offset of x so top is 0. That will use internally G92 to set an offset so negative Z is still allowed.
An other solution is disable target position checking with G1 S1.