Here is example code that we use...  This is from an AB CNC but the principals should apply just the same.

N5000 M38  <--- change to low gear
N5010 M04 S20 <---set slow speed
N5020 M06 T421 <----- offset 21 is the adjustment for position
N5030 G91 <--- set relative movement
N5040 G04F1 <---- pause for 1 second
N5050 G33 Z-.100 K.20 <--- threadcut for .20 + offest
N5060 M05  <--- stop motion
N5070 G01 Z.100 T400 <--- reset to starting position
M30 <----- rewind

Hi pabeader,

this looks very interesting, I will give this a go when I have finished installing the new spindle motor and inverter.

Thanks for that.

Graham