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Watch Solutions for Hard Milling
Makino demonstrates the latest techniques and technologies for high-speed machining of hardened materials for die or mold applications. Check out tips, tricks, and new technologies you can use to mill the toughest steels, shortening your lead times, lowering your costs, and eliminating bench work.

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When cutting 60 Rockwell, be aware that there are cutters specifically designed for this material. Using anything less will cause unwanted results.

If you want to get to a bench-free surface finish and want that part to have an accuracy based on being able to shoot a mold, you need to be mindful of the tolerance specifications of the cutter. For instance, if I'm cutting half of my parts to zero and half of my part to negative stock and I want to make sure that on my parting surfaces are closing. I must pay attention to the tolerances of the tool to make sure this will happen without bench-time.

Geometry also plays a part in tools designed for 60+ Rockwell. Because the tools are designed for hardened materials, their cutting angles vary according to the manufacturer's testing. There are ballnose endmills like the OSG SHP series that has a 15 degree angle on the cutting edge around the cutting flute. There is also what is known as a true four flute ballnose endmill that has 30 degrees on the cutting angle. Kind of goes against the 15 degrees and the two flute ballnosed endmill but because this is a four flute and it is a true four flute which means that the cutting edge comes all the way to the center this tool is actually 30 degrees. A high helix angle or a 45 degrees doing a six fluted cutter which would have a 45 degree angle on it going long depth but shallow step over or shallow radial step over. Choose a tool that fits the specifications you are looking to achieve in your hard milling application, keeping in mind that there are several options out there.

In order to allow for decent tool life in such hard materials, most manufacturers add a coating to their tools. A Hitachi TH coated endmill or a ballnose endmill is an example. The coating makes the tool a gold color. Other examples include OSG with the Max series as well as their SHP series, Mitsubishi has Impact Miracle, NS has Mugen, Polkom has PVAT, and Union Tool has what they call the Hard Max coating. All are excellent for 60+ Rockwell applications.

Next we are going to talk about CBN. Maybe you have done your own research on CBN cutters and found them be very expensive. Despite the expense, CBN cutters are very good at providing extended tool life and excellent finishing when milling hardened materials. A CBN cutter is typically used after a semi-finishing or even a finishing routine and take off less than a thou of material. In most cases, if I'm using a ballnose endmill, I might only be taking off half a thou. There are several options out there as well. There are insert type. An insert type would be say a button type cutter might only be ninety bucks. There is also the solid type, like the OSG CBN cutter. If your primary concerns are finish and tool life when cutting hardened materials, a CBN cutter might be the way to go.