I'm trying to model "Prism carved letters". My company does a lot of these - see pic below.

We currently make them by cutting the shape of the letter out with a band saw/ jig saw, then cut the angled faces with an overhead router. (bearing runs on the edge of the letter), then finish carving the "valleys" that the router can't get into by hand. However we are looking at doing these on a CNC router, so we need to model them. I'd also like to be able to render designs for the client prior to production.

I've tried several techniques, but can't make anything work consistently. The "A" below was created with extrude, then extrude with draft. It worked.

The "C" below was created using the same method, but I can't make it work. (The red faces should not be there). When I increase the height of the extrude beyond what is shown in the screen shot, the extrude fails (the geometry around the red tear drop shaped face puckers)

I know that some CAM programs have this functionality built in, however I want to be able to do it in SW.

Any advice would be appreciated....