Shaping internal gears

Shaping internal gear cutters
Ivan Laws book gives detail of making cutters for spur gears but how do you go about making cutters for internal gears other than "by eye"? I am trying
to have a go at making a 32 dpi internal gear by shaping on the lathe.
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from "DaveC"

W. O. Davis' book "Gears for Small Mechanisms" has skant reference to internal gears but pages 82/83 do show the form for a broach, along with formul for the basic flank radius and thickness for gears with more than 50 teeth. How you are going to create an accurate 'shaping cutter' for the form I leave to your own devices :)
I've sent a .PDF to your referenced e-mail address.
JG
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