This is a board that I created on Fritzing and had it fabricated by OSH Park earlier this month. The gerber I used in CopperCam is the same one I sent to OSH Park. Below is a sample of the g-code I generated from this gerber. This board has 8 mil trace and a few 0.3 mm laser drill holes, and is not likely it could ever be milled on a cnc machine. I didn't set anything up on CopperCam, this was generated out of the box.
I had thought about building another cnc machine and trying this out... sounds like a good winter project...
Yes, a board can be cnc milled using Fritzing gerbers... You may need to design the board a little different than you would for a fab shop.
BTW, CAD/CAM and CNC machining is my background...
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( CopperCAM - 14/10/2016 / ISO-Mill Output )
( C:\COPPERCAM\CopperCAM.iso created 18/10/2016 at 20:29 )
( Workpiece dimensions: 33.528 x 57.836 x 1 mm )
G21 G40 G54
G80 G90 G94
T3 M06 ( Basic Drill )
M03 S12000
M07
G00 X21.841 Y8.611
G00 Z0
G01 F60 Z-1
G00 Z2
G00 Y6.071
G00 Z0
G01 F60 Z-1
G00 Z2
G00 Y3.531
G00 Z0