Hey Brian,yeah .GPI is what the CAM in Eagle,(this has become one of the most popular and powerful,I have no affiliation, PCB CADs puts out in another ,starting to become defacto gerber generation segment(there are actually many Gerber configurations)called GERBER_RS274X. But still,most of these files generated get pretty big and I suggest anyone interested in using Mach3 for this purpose to get a license because most boards will easily surpase 1000 lines.And if you try and minimize the geometry,it most likely will screw up the nuances of the board. At the moment,LCAM will not make good use of being able to utilize the 'image' import in LCAM that Eagle can put out as a .BMP,last I checked.-Keith