I just output an NC file from Mastercam, and brought it into Mach3 to inspect. Mach3 has been set to mm (for units) and Mastercam file was designed in mm as well.

I have also included a screenshot out of Mach3.

SIDE-TAKE02.NC

%

O0000(TOP SIDE-TAKE02)

(DATE=DD-MM-YY - 29-04-12 TIME=HH:MM - 22:51)

(MCX FILE - V:\ADRIAN\AF ASSIST TOOL\V3.1\MILLING THE CASE POCKETS\TOP SIDE\TOP SIDE-TAKE02.MCX-6)

(NC FILE - V:\ADRIAN\AF ASSIST TOOL\V3.1\MILLING THE CASE POCKETS\TOP SIDE\TOP SIDE-TAKE02.NC)

(MATERIAL - ALUMINUM MM - 2024)

( T210 | 1. FLAT ENDMILL | H210 )

N100 G21

N102 G0 G17 G40 G49 G80 G90

N104 T210 M6

N106 G0 G90 G54 X-37.5 Y-28.9 S3000 M3

N108 G43 H210 Z5.

N110 Z2.

N112 G1 Z-.5 F400.

N114 X-38.5

N116 G2 X-39.5 Y-27.9 R1.

N118 G1 Y-22.4

N120 G2 X-39. Y-21.9 R.5

N122 G1 X-21.

N124 G2 X-20.5 Y-22.4 R.5

N126 G1 Y-33.4

N128 G2 X-21. Y-33.9 R.5

N130 G1 X-39.

N132 G2 X-39.5 Y-33.4 R.5

N134 G1 Y-27.9

N136 G2 X-38.5 Y-26.9 R1.

N138 G1 X-37.5

N140 G0 Z4.5

N142 Y-28.9

N144 Z1.5

N146 G1 Z-1.

N148 X-38.5

N150 G2 X-39.5 Y-27.9 R1.

N152 G1 Y-22.4

N154 G2 X-39. Y-21.9 R.5

N156 G1 X-21.

N158 G2 X-20.5 Y-22.4 R.5

N160 G1 Y-33.4

N162 G2 X-21. Y-33.9 R.5

N164 G1 X-39.

N166 G2 X-39.5 Y-33.4 R.5

N168 G1 Y-27.9

N170 G2 X-38.5 Y-26.9 R1.

N172 G1 X-37.5

N174 G0 Z4.

I have also tried other post processors out of Mastercam which output IJ arcs, and identical results come out of Mach3

What am I doing wrong?