Q01. Spur Gears Mixed-teeth Profiles
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This is a three-tooth pinion which was used in hoisting machinery. The curve of the smaller gear is an involute and the curve on the larger gear is obtained by rolling one circle on another, ie an epicycliod. According to Reuleaux, this mixed-tooth shape was chosen to avoid too much undercut on the pinion.

Reference :
Gelsone, Kathryn (Technician)
Peck, Susan (Technician)