A milling cutter is round, so it cannot cut a perfectly sharp internal corner. Specifying a sharp corner forces extra operations—or leaves a radius you did not plan for.
The geometry reality
End mills leave a radius equal to their diameter at inside corners. To get a “sharp” corner you must add a smaller tool, a ramped finish pass, or EDM—all adding cost.
The better choice
Add an internal radius. A radius of 0.5–1 mm lets a standard tool finish the corner in one pass. Larger radii let larger, faster tools cut the whole pocket.
Design rule
Set the corner radius close to the pocket depth or feature size. The bigger the radius relative to the tool, the faster and cheaper the cut.
FAQ
Can I get a truly sharp corner? With EDM or a tiny tool—at a cost. Default to a radius.
What radius should I pick? 0.5–1 mm minimum; larger where possible. See DFM basics.
