You’ve heard of round-over router bits, but how about round-under bits? Round-under bits allow you to form the bottom edge of a bull nose without turning the material over. Combined with the matching round-over bit, you can form a full bull nose. There are two reasons you’d want to use this bit: Either the material is too heavy and/or awkward to turn over easily, or you want to form the edge with a countertop in place.
A few companies make these bits, but we’ll look at Amana Tool’s offerings. They sell three round-under bits with 1/2″, 3/4″, and 1″ radii for solid surface materials. The largest bit, the 1″ radius, is so large that you need to make sure to keep it spinning under 14,000 RPM. So you won’t mar the finish, they use their Ultra-Glide Delrin sleeved ball bearing guides rather than steel ball-bearings guides.
Pricing for the bits starts at $100 for the 1/2″ radius bit and up to $150 for the 1″ radius bit.