Ok so I am new to this and just got my CNC (x2 mill DIY converted to CNC, MACH3 and Fusion360) working my first project. So I am trying to cut .043 hole in 01 tool steel. For practice I have been playing with 1/16" cold rolled steel plate. I had luck using a .043 Colbat Endmill cutting this slot so I thought I would try the tool steel. 1/16" tool steel plate. I was using like 2000 rpm at 3IPM feed. Broke 2 of these Niagara cutters. So guys whats the answer? I sure appreciate the help!