Page 235 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 7 Bearings, Couplers, Gears, Screws, and Springs 213

FIGURE 7-27 Spur gear anatomy

NOTE Remember that the diametral pitch and circular pitch of all meshing
gears must be the same.

• Circular pitch (p) = / P The length of the arc between the center of one
tooth and the center of a tooth next to it. This is just pi (π = 3.1416) divided
by the diametral pitch (P). Although rarely used to identify off-the-shelf gears,
you may need this parameter when modeling gears in 2D and 3D software
(see Project 7-1).
• Outside diameter (D ) The biggest circle that touches the edges of the
O
gear teeth. You can measure this using a caliper like SparkFun’s TOL-00067.