The nose radius is the slight rounding at the tip of a cutting tool (insert).
It is also written "nose R."
It is expressed as a size such as R0.2 or R0.4.
The tip is not perfectly sharp; it is deliberately given a small radius.
A Closer Look
There are two reasons for rounding the tip.
One is edge strength: a rounded tip is less likely to chip during machining.
The other is surface finish: the larger the nose radius, the smoother the machined surface.
The nose radius also has a side effect.
On tapers (angled cuts) and arcs (curved surfaces), the rounding leaves material uncut or removes too much, producing shape errors.
A function called "nose radius compensation" cancels this error automatically.
Enjoying the benefits of the nose radius while compensating for its error is what leads to high-precision machining.