Pitch Diameter

Pitch Diameter

Pitch Diameter
The diameter of the circle on a gear determined by dividing the number of teeth in the gear by the diametral pitch. In parallel shaft gears the pitch diameters can be determined directly from the centre distance and the numbers of teeth by proportionality. Operating Pitch Diameter (Working Pitch Diameter): the diameter of the circle on a gear which is proportional to the gear ratio and the actual centre distance at which the gear pair will operate. A gear does not have an operating pitch diameter until it is meshed with a mating gear. Generating pitch diameter: the pitch diameter at which the gear is generated. In a bevel or hypoid gear, the pitch diameter is understood to be at the outer ends of the teeth unless otherwise specified.
Whereas: From Gear Data M_n = normal module pitch (8) DP_n = normal diametral pitch (3.175) ß = helix angle (15) z = no. teeth in gear (61) C' = operating centre distance of mesh () z1 = number of teeth in pinion (17) z2 = number of teeth in gear (61) m_g = gear ratio (3.588235294)
Formula: Pitch Diameter: D' (known -M_n) = (z* M_n)/cos(ß) = (618)/cos(15) = 488/0.965925 = 505.215mm Pitch Diameter: D' (known -DP_n) = z/(DP_ncos(ß)) = (61/(3.175cos(15)) = 61/(3.1750.965925) = 61/3.066811 = 19.890inches Gear Ratio: m_g = z2/z1 = 61/17 = 3.588235294 Operating Pitch Diameter - Pinion: d' = (2*C')/(m_g+1) =