[freebeard]

Assume 1" material; then if the inner radius is 3" the outer radius is 4", difference in circumference is ~6 1/4". Around a 90° corner the difference is ~1 1/2", so 1.5 divided by the width of each cut gives you the number of cuts, spread across 1/4 of the inner circumference — 4 1/2".

...approximately.