How do I make every corner at least as big as my bit's radius in one go? (The offset out, in, out trick, and when you don't need it)

First, decide whether you need to do anything

Forum veterans point out that a flat end mill already leaves inside corners at its own radius. A 1/4 inch bit gives 1/8 inch inside corners whether the drawing shows a sharp corner, a 1/8 inch fillet or a bigger one, so for ordinary pockets and inside profiles you can leave the vectors alone. You only need to edit the geometry when the piece has outside corners or tight convex bends that a mating part must fit around, or when the shape is cut all the way through and both faces will show, as with a through inlay.

The three-offset recipe (users report it works)

Using Offset Vectors with Create sharp offset corners left unchecked, for a 1/8 inch minimum radius:

1. Select the vectors and offset Outwards by 0.0625 inch (half the radius).
2. Offset the result Inwards by 0.125 inch (the full radius).
3. Offset that result Outwards by 0.0625 inch.

The outward pass rounds convex corners, the inward pass rounds concave ones, and the last pass returns the outline to size. One member tested the geometry and warned the result is not exactly a 0.125 inch radius at every corner, so measure a sample corner and adjust the three distances. A user-written gadget that automates the sequence is shared on the forum's gadget board. The person who asked confirmed this was what they needed.

When you want exact fillets instead

Create Fillets with Normal Fillet and the radius typed in. In the 3D view the software previews the fillet before you click, and you can type a new radius while hovering. For slots that must accept a square part, use the Dog-Bone or T-Bone fillet types.

Pro tips

• For a fitted insert, consider the Inlay Toolpath, which calculates pocket and insert together (see the inlay entries).
• Offsets add vectors, they do not replace them; work on a copy of the layer and delete the two intermediate results.
• If Create sharp offset corners is checked, the trick does nothing.