What Chuck said...
Use a ball nose endmill..
i found it easiest and best to use the surface rough pocket feature in mastercam... give it a helical entry and go from there...
i's rough it out with a regular indexable endmill and then go in and semi finish it and then finish it with the ball nose...
at 6", you are going to get deflection and chattering.
try using an indexable ball nose cutter |