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None of the above is anything to do with the cutter number to be used. The cutter number changes from that used for a spur gear (helical gear with a helix angle of zero) because the teeth on the normal diametric pitch are on an ellipse, not a circle. The local radius of the ellipse is larger than the radius of the blank. So the equivalent number of teeth is larger than the number of teeth on the actual gear. The cutter number is selected according to the equivalent number of teeth, not the actual number. The equivlant number of teeth is the actual number of teeth divided by the cosine of the helix angle cubed:N' = N/cos3(A)