1. Gears

2. A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit to torque. (Wikipedia) Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. (Wikipedia)

3. Spur Gear Parallel axis Helical Gear Parallel axis Helicoid teeth Skew Gears Axis at right angle and do not intersect Double Helical Parallel axis Right & Left helical teeth Balances axial thrust forces Bevel Axis at right angle and intersect Cone Shaped

4. Spiral Bevels A bevel gear with angled spiral teeth Hypoid Common in differentials Hypoidcycle teeth Crown (contrate) Type of bevel gear Worm Axis at right angle and do not intersect One gear is in the form of a worm Rack and Pinion Rack is straight gear Transmits linear motion Non-Circular

18. http://www.excelcalcs.com/repository/m achines/gears/involute-coords.xls/