We use a special cutter we have made for us. There is 4 angles, each has a different thickness and after cutting there is a nice big ledge where the cutter digs into the bowl.
We blend that out...that's it. Just smooth the casting into the bottom cut. I leave all the angles there too, no extra blending.
The top cut is left nice and wide, and I'm carefull not to cut the valve job too deep and leave a ledge in the chamber.
One other thing...the back cut on the intake valve is healthy!
Hope that helps some...
Brian