Corner Rounding End Mill Sharpening....?

[EmilioG]

I have a few CR end mills that are not dull but not super sharp either. The geometry looks very simple, close to a countersink.
Does anyone know how to sharpen these cutters w/o ruining them? I own three and they're all HSS bright. Can I simply stone the edges lightly?
What type of stone is best or should I use a diamond hone?

 

[Bob Korves]

A stone will work, but a bench grinder is a lot faster. Just try to keep the actual cutting edge round (or the shape you want it), and make sure you have enough relief in all directions behind the cutting edges. I have many dozens of them which were done by another machinist, little doubt but that they were made from standard end mills with chipped corners. I have used some of them and they work just as well as the ones made that way from the factory. After a oops and some swearing, grinding to a ball end mill comes next.

 

[benmychree]

Some of them that I have had and seen are form relieved and can be sharpened by grinding on the FACE of the cutter, NOT the radius; this is best done with a cutter grinder so that all the teeth are ground to the same dimension so that they all cut.