What is undercutting of gears?

Answer 1

Undercutting of gears, is machining a matched set of dogs/slots that grip into each other - so that they will grip harder the more torque the engine is providing. This will prevent the gears from slipping out again after initially having them engaged. An easy setup, is to fix the gear with its axis center offset in an indexing head - sligthly tipped over(3 to 5 degrees - depending on how much material that can be removed, or how badly the dogs are worn), so that the actual dog to be machined spins precisely around its own vertical axis when table is turned. The finished dog, will have a uniform shape all the way around its contact areafacing the slots/dogs of the interacting gear next to it.

Usually done in a vertical mill, by grinding - or with a dovetail milling bit. Using a dove tail milling bit, will let the machinist fix the gear in a horizontal position, rather than having to tilt it the neccessary amount of degrees. Dogs, slots - or teeth, need to be hardened again, if they are ground beyond the limit of the previous hardened surface of the material.