Corner Radius End Mills [Bull Nose]: Guide

What is a Corner Radius Endmill (or Bull Nose end mills)

Corner radius end mills also called bull nose end mills) are normal square end mills that have a slight radius ground into their edges. The radius helps distribute cutting forces evenly to prevent damage to the end mill, which extends its life.

While they cost a bit more than normal square end mills, the extra cost may be worth it in terms of potential higher performance and longer tool life.

Normally, the corner radius can be had in a variety of radius sizes.

This diagram shows where the corner radius may be found (marked via “R”):

Are Corner Radius End Mills for Roughing or Finishing?

Yes. In other words, they’re good for both. The corner radius makes the cutting edge less susceptible to chipping, which makes them ideal for roughing. In fact, many cnc machinists insist on bull nose end mills when roughing, especially on tougher materials.

They can also be excellent in micro-milling applications because the rounded corner makes the tool tougher.

But, in addition, if your work can accept the radiused edge, they will also give a finer finish than a square end mill. Even if you have to use a square end mill as your finisher, it will last longer if the rough cut was performed with a corner radius end mill.

Corner Radius End Mill Feeds and Speeds

A Corner Radius End Mill can run with faster feeds and speeds than a square end mill.  You can use our G-Wizard Feeds and Speeds Calculator to figure out just exactly how much faster they can go.

Specifying a corner radius end mill in G-Wizard is simply a matter of setting the Corner Rad. field to the corner radius.

Quality Control Issue: Edge Blending

One of the most common problems you can see is poor blending of corner radius end mills. If the radius in not tangent or more commonly referred to as an “undercut” or “step”. Avoid corner radius end mills that have a step visible on the radius.