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Try G51 X0 Y0 I-1000 J-1000

This will scale around point X0 Y0, with a scale factor of 100% (full size) and the - (minus sign) means it will mirror it in this plane.

So to mirror in X but not in Y use I-1000 J1000. Or just leave the J out. G51 X0 I-1000


Use G50 to cancel G51.

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