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Rules &
Formulas

Diametral Pitch
Spur Gears

TO GET HAVING RULE FORMULA
Module Diametral pitch Divide 25.4 by the diametral pitch m=25.4/Pd
Diametral pitch Module Divide 25.4 by the module Pd=25.4/m
Circular pitch Divide π by the circular pitch Pd=π/P
Pitch diameter and number of teeth Divided the number of teeth by pitch diameter Pd=N/D
Outside of gear and number of teeth Divide number of teeth plus 2 by the outside diameter Pd=N+2/Do
Base pitch and pressure angle Divide the base pitch by the cosine of the pressure angle then divide by π Pd=(Pb/cos.Φ)/π
Operating diametral pitch Center distance between 2 gears and no. of teeth in both Add the no. of teeth in both gears and divide by 2, then divide by center distance dp= (n1+n2/2)/C
Pressure angle Base diam.. and pitch diam. Divide the base diameter by the pitch diam. cos.Φ=Db/D
Base pitch and diametral pitch Divide π by the diametral pitch, then divide by the base pitch cos.Φ=Pb/(π/Pd)
Base pitch and circular pitch Divide the base pitch by the circular pitch= cosine pressure angle cos.Φ=Pb/P
Pitch Diameter Number of teeth and diametral pitch Divide the no. of teeth by the diametral pitch D=N/Pd
Number of teeth and outer diameter Divide the product of the outer diam.. and number of teeth by number of teeth +2 D=NDo/n+2
Outside diameter and diametral pitch Subtract from the outside diameter, the quotient of 2 divided by the diametral pitch D=Do-2/pd
Addendum and no. of teeth Multiply addendum by the no. of teeth D=an
Base diameter and pressure angle Divide the base diameter by the cosine of the pressure angle dp=Db/cos.f
Outside Diameter Number of teeth and diametral pitch Divide no. of teeth plus two by the diametral pitch Do=N+2/Pd
Pitch diameter and diametral pitch Add the pitch diameter to the quotient of 2 divided by the diametral pitch Do=D+2/Pd
Pitch diameter and number of teeth Divide the no. of teeth plus 2 by the quotient of no. of teeth divided by the pitch diameter Do=N+2/N/D
Number of teeth and addendum Multiply the no. of teeth plus 2 by addendum Do=(N+2)a
Number of teeth Pitch diameter and diametral pitch Multiply pitch diameter by the diametral pitch N=D•Pd
Outside diameter and diametral pitch Multiply outside diameter by the diametral pitch and subtract 2 N=DoPd-2
Std. thickness of tooth Diametral pitch Divide 1.5708 by the diametral pitch t=1.5708/Pd
Std. addendum Diametral pitch Divide 1 by the diametral pitch a=1/Pd
Std. Dedendum Diametral pitch Divide 1.157 (or 1.25) by the diametral pitch b=1.157/Pd
Std. whole depth Diametral pitch Divide 2.157 (or 2.25) by the diametral pitch ht=2.157/Pd
Clearance Diametral pitch Divide .157 or (.250) by the diametral pitch  c= .157/Pd
Thickness of tooth Divde thickness of tooth at pitch line by 10 c=t/10
Center distance Normal diametral pitch and no. of teeth in both gears Add no. of teeth in both gears and divide by 2, then divide result by the normal diametral pitch dp=((n1+n)2/2)/Pnd
Operating center distance Operating diametral pitch and no. of teeth in both gears Add the no. of teeth in both gears together and divide results by 2, then divide results by operating diametral pitch dp=(n1+n2/2)/Pod
Base diameter Pitch diameter and pressure angle Multiply the pitch diameter by cosine of the pressure angle  Db=DcosΦ
Base pitch Diametral pitch and pressure angle Divide the diametral pitch by π, then multiply by cosine of pressure angle Pb=cos.Φπ/Pd