What is the deepest plunge you would make with a 1/4 inch flat end mill on a 1/2 sheet of Luann? One website days1/2 inch diameters x 2 . Is this alright?
one-half the endmill diameter is a decent guideline.
Per http://docs.carbide3d.com/support/#tooling-support depth per pass (D.o.C., depth of cut) is 0.25" in plywood.