Cutting sharp square internal corners , newbie

[Neale]

Simple answer is that you can't cut a square internal corner with a round tool! What is generally done is either you accept round corners and machine the mating part to fit, or you machine a relief in the corner by over-cutting slightly so that there is clearance for the sharp corners of the mating item.

You say that you are using Cut2D. I use Cut3D and it has a feature that lets you add these fillets to a design. It's very much a 2D feature so I would be surprised if your software didn't include it as well. There is a choice of style of fillet, even, and it's as simple as selecting the tool and clicking on the corner on the drawing. Using a small tool, the result is fairly discreet.

EDIT: Just been checking and it's VCarve that has the filleting feature, not Cut2D/Cut3D. You can add these fillets manually, of course.