We use .118 cutters in our PRC rail cutting machine.
Carbide Cutter Installation Instructions
The set screw than holds each carbide cutter was adjusted before shipping, and should not normally need adjustment. If there is any up and down movement, or if you are installing new cutters, carefully adjust the set screws located in the center of each cutter housing to keep the cutters pressed down onto the fixture to get an accurate cut. Cutters should not have any vertical play, but should still move back into housings when pushed in by hand (though with some effort) when the adjustment knobs are retracted. VERY IMPORTANT: If the set screws are too tight you will chip your carbide cutters on the retract stroke of the car. They cutters must be loose enough that you can push them with your fingers. Also, never reverse the screw when in the middle of a cut. That will also chip the cutters.