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Originally Posted by sanddrag
Anyhow, now that I know they are not the same, is there any way I can derive the correct internal profile from the external profile I have? I can't draw a proper single tooth. See, I need the drawing to be involute so I can take this drawing somewhere to be manufactured (edm, perhaps laser, etc.). I have a program (Geargen) that will make an involute external gear in a dxf, but not internal. Can I somehow convert it in Inventor or AutoCAD? Or are there any other programs that will make the drawing?
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If you can generate the proper involute curve for an external tooth gear of the required pitch, then you are nearly done. The tooth form for an internal gear is the inverse of the external involute (in fact, my old copy of
The Handbook of Gears gives the formulae for determining gear tooth thickness at any point on the addendum or dedendum for both external and internal gears, and they are identical save for the note that when calculating for internal gears "it is the tooth space that is calculated and the internal gear tooth thickness is obtained by a subtraction from the circular pitch at that radius.").
-dave