There are four common tool types to consider for cutting pre-hard materials: ball-end, toroidal, multi-fluted bull-nose and square-end.
If you have tight areas like helical bores or ribs, or when the cutter diameter is close to the radius of the part, the optimal choice is a toroidal tool. These cutters are able to cut flat floors with larger stepovers than ball-nose cutters, but are much better suited for tight areas.
When using toroidal tools for profiling applications, the hardness of the material affects the radial stepover. For materials 30-50 HRc, use a stepover of 5 percent of the tool diameter per pass, and if the material is harder than 50 HRc, use a stepover of 2 percent. In both cases, you can use a Z depth of one time the diameter of the cutter per pass. When facing on flat floors or doing helical bores, the radial stepover is 25 percent of the cutter diameter and 2 percent in Z depth per pass. If going down in a helix, use a two- to three-degree helix angle.
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