What is a proper speed for countersinking?

Slow it down until it stops chattering.

Jim

"Alex" wrote in news:1137615041.876778.293340 @g49g2000cwa.googlegroups.com:

I usually csk at between 60 and 100 rpm. Remember that your sfm calculations won't be very accurate because you have both a continuously increasing diameter, and a continuously increasing tool surface contact. The higher the surface contact of the tool, the higher the horsepower required, the higher the loads on the tool and workpiece and the more rigidity you need, which is why it doesn't start chattering usually until you get half way or more into the csk.