Page 110 shows which way to move but basically you want the middle of the cutter to still line up with the ctr of the cut at its inner end so if your roll rotation makes the groove lower then lower the tool, if when you roll the gear the groove is above ctr then raise the tool.

Edited By JasonB on 23/04/2019 07:07:28

I don't think it will make a lot of difference, not sure what size your gear is but if say 2" dia then it is only a thou off the tooth at its outer edge. If you recalculate the offset to this new angle then that should be reduced.

I suppose you could work out the roll for the other gear and go the opposite way so you either have big gaps with big meshing teeth or small gaps in this wheel with larger teeth on the pinion.

Edited By JasonB on 23/04/2019 08:40:31

On page 111 of the gear cutting book about three quarters down the first
column it explains the principle to get the blank roll.
For example to get a thirty tooth gear using your 72 :1 table
and using a 60 hole division plate= 72 x 60 = 4320 holes
for one complete revolution of the rotary table ,divide by
30 = 144 holes or 2 turns and 24 holes.
The blank roll would be 36 holes in the 60 plate.
The important point made in the book is that the dividing plate
must be able to be divided by 4.
You could of course if the plate is only divisible by 2 make
the cuts in the gear in 2 passes missing out the initial centre
gashing cut ,same page second column.

I see from your later posting that you have a 15 hole plate ,
the easiest solution is to use this and make a 60 hole plate
and from there the 20 tooth gear =72 x 60 = 4320 holes
for 1 revolution of the RT, divide by 20 = 216 holes or
3 turns and 36 holes ,the blank roll = 54 holes.
For the 40 tooth gear = 72 x 60 = 4320 holes for 1
revolution of the RT, divide by 40 =108 holes or
1 turn and 48 holes ,blank roll = 27 holes.

The sizes of the gears at the large end do not influence
these calculations ,trying to work out the rotation of the blank
roll in degrees will only lead to mistakes.

John