Surface contour toolpath (odd)

Hi Folks,

I'm in Mastercam X trying to do a contour surface finish toolpath.

The geometry I need to cut looks like a funnel in a block of
metal with 4 vertical slots cut into the funnel. I've created surfaces on the inside of the funnel and over the slots too.

When I specify a 1/4" ball endmill Mastercam has the tool rising and skipping (retracting) over a small section of the then coming back down to the inside surface and cutting almost like the toolpath is stuttering or jumping over a feature when no feature is there.

Yet when I specify a 1/4" flat endmill the tool path is nice and smooth.....no retracting.


I do get the message"Check and drive stock to leave are identical. Adjust check stock
by plus or minus cut tolerance for crisper tool motion near sharp corners formed by check
and drive geometry.

Any ideas?

Thanks
John

Email me your file or post it here and I will review and answer.