Can somebody please tell me how to write the code to allow me to use a different cutter on my CNC router table programme so I can use  a 3mm cutter on a programme written for a 5mm cutter. The manual says G42/G43 but I don't know how to use it.
I've listed the 3mm cutter on my Tool Table as Diameter -2mm because the G Code was written on Sheetcam for a 5mm cutter & Mach3 shows the tool for the 5mm cutter as T1 Diameter 0. Is this correct ?
I've written G42 T2 (I've tried it everywhere between line 9 & 15). I've also tried G42 X-2.0 Y-2.0 & a few other codes but Mach3 still runs the cuts for the 5mm cutter.
In the code below what would I write to change the toolpath for the smaller cutter please ?
Is there a setting somewhere I also need to change ? Please keep as simple as possibe because I am (as simple as possible).

N0000 (Combined L & R Fig12 Targets with offset shift)
N0010 (Post processor: Mach2.post)
N0020 (Date: 20/04/2007)
N0030 G21 (Units: Metric)
N0040 G40 G90
N0050 F1
N0060 (Part: ~$Fig12RHmod001)
N0070 (Process: Outside offset 0, Mill/Router, 5 mm diameter, 5 mm Deep)
N0090 M06 T1  (Mill/Router, 5 mm diameter)
N0120 M03 S500
N0125 G00 Z40
N0130 X-325.5000 Y231.0000
N0150 G00 Z0.0000
N0160 Z-15.0000
N0170 G01 X122.0979 F1500 etc etc . . .

Why not run sheetcam again and post the code out for a 3mm cutter?

Or try it like this :-

N0000 (Combined L & R Fig12 Targets with offset shift)
N0010 (Post processor: Mach2.post)
N0020 (Date: 20/04/2007)
N0030 G21 (Units: Metric)
N0040 G40 G90
N0050 G43 F1
N0060 (Part: ~$Fig12RHmod001)
N0070 (Process: Outside offset 0, Mill/Router, 5 mm diameter, 5 mm Deep)
N0090 M06 T1  (Mill/Router, 5 mm diameter)
N0120 M03 S500
N0125 G00 Z40
N0130 X-325.5000 Y225.
N0150 G00 Z0.0000
N0160 Z-15.0000
N0170 G01 G42 D2 Y231.
X122.0979 F1500 etc etc . . .

Graham.

Thanks Graham. There was a lot of work making fine manual G code entry adjustments so the cut would fit the molded product & I wanted to avoid doing it all again.