[scottandme]

Ramp in to the cut, don't straight plunge. Should be trivial to do in Mastercam.

4075 RPM @ 12.2 IPM (200SFPM & 0.0015 inch/tooth) - full slot with 0.09" DoC gives me an estimated 0.002" of tool deflection (1" stickout guess). Not good when your chipload is smaller than the cutter deflection.

4075 RPM @ 8 IPM has 0.018" of deflection, but chip load is only 0.001 inch/tooth there.

Unless there's some crucial need for a 3/16" cutter, go with a bigger end mill. If you need to you can always do a cleanup pass with a smaller endmill after roughing out the shape.