Perdón por la demora, no había visto la respuesta.
G64 es modal, escribila al principio:
N0G90
N10 G64 ( <-- por ejemplo )
N20M6T1
N30M3 S18000
N40G0 X8.764 Y18.331 Z6,000
N50G1 Z-10,000 F762.0
N60G3 X20.264 Y6.831 I20.264 J18.331 F2540.0
N70G1 X100.264
N80G3 X111.764 Y18.331 I100.264 J18.331
N90G1 Y98.331
N100G3 X100.264 Y109.831 I100.264 J98.331
N110G1 X20.264
N120G3 X8.764 Y98.331 I20.264 J98.331
N130G1 Y18.331
N140G0 Z6,000
N150M30