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4.1.2 Symbols

The symbols used in this section are summarized below.This is consistent with most gear literature and the publications of AGMA and ANSI.

SYMBOL NOMENCLATURE & DEFINITION
B

backlash, linear measure along
pitch circle

 a addendum
BLA backlash, linear measure
along line-of-action		 b dedendum
aB backlash in arc minutes  c clearance
C center distance d pitch diameter, pinion
D change in center distance dw pin diameter, for over-pins
measurement
Co operating center distance e eccentricity
Cstd standard center distance  hk working depth  
D pitch diameter ht whole depth
Db base circle diameter mp contact ratio
Do outside diameter n number of teeth, pinion
DR root diameter nw number of threads in worm
F face width pa axialpitch
K factor; general pb base pitch
L length, general; also lead of worm pc circular pitch
M measurement over-pins pcn normal circular pitch
N number of teeth, usually gear r pitch radius, pinion
Nc critical number of teeth for no undercutting rb base circle radus, pinion
Nv virtual number of teeth for helical gear rt fillet radius
Pd diametral pitch ro outside radius, pinion
Pdn normal diametral pitch t tooth thickness, and for
general use for tolerance
pt horsepower, transmitted yc Lewis factor, circular pitch
R pitch radius, gear or general use g pitch angle, bevel gear
Rb base circle radius, gear q rotation angle, general
Ro outside radius, gear l lead angle, worm gearing
RT testing radius m mean value
T tooth thickness, gear v gear stage velocity ratio
Wb beam tooth strength f pressure angle
Y Lewis factor, diametral pitch fo operating pressure angle
Z mesh velocity ratio y helix angle (Wb = base helix angle;
operating helix angle)
w angular velocity
invf involute function

4.2 Pitch Diameter and Center Distance

As already mentioned in par. 2.4, the pitch diameters for a meshing gear pair are tangent at a point on the line-of-centers called the pitch point. See figure 1.4. The pitch point always divides the line of centers proportional to the number of teeth in each gear.

          Center distance = C  =  D1 + D2 = N1 + N2                                                                          (5)
                                                   2            2Pd

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