[Jim27]

Looking at machining some harder steels - HT 4340 at Rockwell C of 30 and possibly some close to 60. Saw a little on using endmills with small radius on the tips - 0.010 to 0.030 radius. Seems like that would make the end mill less likely to chip. They cost a bit more. What are the pros and cons? Depending on the application the small radius on the inside corner may not be an issue and would lessen the stress riser of the corner.

[Jim Dawson]

You mentioned all of the up sides to using them. There really is no down side. Just depends on your application, and for what you would be using them for they seem like a good fit.

[OldSchoolProgrammer]

I agree with Jim Dawson. If a part function wouldn't be compromised by having the radius, you're better off with the radiused tools. Also, cutting a small radius in the bottom of shaft key seats of ANY material reduces the stress concentration at the junction of wall and bottom of the key seat. I would go with the largest radius allowed on a particular part.