A corner radius on an end mill replaces the sharp 90-degree corner with a small curve. Tiny radii strengthen the edge for roughing tough materials; larger radii cut intentional fillets into the part.
| Corner radius (in) | mm | Common use |
|---|---|---|
| 0.005 | 0.13 | Strengthen the edge for tough alloys |
| 0.010 | 0.25 | Light edge protection, semi-finish |
| 0.015 | 0.38 | Roughing in steel and stainless |
| 0.020 | 0.51 | General roughing durability |
| 0.030 | 0.76 | Heavy roughing, small fillets |
| 1/64 (0.0156) | 25.40 | Standard small fillet |
| 1/32 (0.0313) | 25.40 | Common fillet radius |
| 1/16 (0.0625) | 25.40 | Larger fillet or blend |
Common stock radii; many sizes are available as specials. A corner-radius (bull nose) tool lasts far longer than a square end mill in hard, interrupted cuts.
FAQ
Should I always use the largest corner radius the tool allows? Not necessarily. A larger radius increases tool strength and edge life but also increases cutting forces and can require slower feeds in shallow cuts, so radius choice should balance part geometry requirements against tool rigidity and finish needs. Match the radius to what the cutting edge and workpiece corner can both tolerate.
See the End Mill Selection Chart.