Making a replacement tumbler gear for one that stripped the teeth.
South Bend gearbox for a 9", 10K, or in this case, the same
gearbox factory fitted for the table feed on the SB Milling machine.
When making only one gear, simplest method of centering cutter is
to make a light pass across the face, rotate the gear 180 by means
of the dividing head, and see if another pass of the cutter is on 
the same line.  Can usually dial in withing 3 iterations.  For that 
and other reasons, the blank is made extra thick, and faced off to 
thicknss after the gear is cut.  Same with the stub flange, which is 
left long at first to increase holding surface on the stub arbor while
cutting the gear teeth.