[SeaBird]

Attachment 419952

Are you using a boundary? Try without.

If you only want to rough the outside, then pick 2 boundaries:-
The 1st the part profile
The 2nd a rectangle bigger than the billet - it's size really doesn't matter as long as the cutter can easily fit between it and the billet. You will have manually create this.

Play with boundary options (in/out etc) in roughing to see different results.