Something like this (below)

40mm square containing a circle.

Spindle speed 12000rpm, tool dia 2.5mm (not critical). DOC 0.4mm, feed rate 800mm/m, plunge rate 300mm/m


Code:
( T0 : 2.5 )
G21 G90 G91.1 G64 G40
G0 Z3.0
( T0 : 2.5 )
T0 M6
( Engrave1 )
G17
M3 S12000
G0 X0.0 Y0.0
G0 Z1.0
G1 F300.0 Z-0.4
G1 F800.0 X40.0
G1 Y40.0
G1 X0.0
G1 Y0.0
G0 Z3.0
G0 X5.8579 Y5.8579
G0 Z1.0
G1 F300.0 Z-0.4
G3 F800.0 X10.0 Y2.6795 I14.1421 J14.1421
G3 X40.0 Y20.0 I10.0 J17.3205
G3 X10.0 Y37.3205 I-20.0 J0.0
G3 X5.8579 Y5.8579 I10.0 J-17.3205
G1 F300.0 Z-0.8
G3 F800.0 X10.0 Y2.6795 I14.1421 J14.1421
G3 X40.0 Y20.0 I10.0 J17.3205
G3 X10.0 Y37.3205 I-20.0 J0.0
G3 X5.8579 Y5.8579 I10.0 J-17.3205
G0 Z3.0
G0 X0.0
G0 Z0.6
G1 F300.0 Z-0.8
G1 F800.0 Y0.0
G1 X40.0
G1 Y40.0
G1 X0.0
G1 Y5.8579
G0 Z3.0
M5
M30