Base Pitch
Corresponding sides of the teeth are parallel curves and the base pitch is the constant and fundamental distance between them along a common normal in a plane of rotation.
In other words, the circumference of the base circle divided by the number of teeth.
The adjacent tooth profiles are parallel curves and the base pitch a constant distance between them, in the direction of rotation it defines the line of action.
Normal Base Pitch: the base pitch in the normal plane.
Transverse Base Pitch: the base pitch in the transverse plane.
From Gear Data
Mn = normal module pitch (8)
an = normal pressure angle (20)
ß = helix angle (15)
x = profile shift coefficient (0)
Calculated
CPt = transverse circular pitch (26.019mm)
at = transverse pressure angle (20.6469º)
Formula:
Normal Base Pitch:
= Pi*(Mn*cos(an))
= 8*cos(20)
= 8*0.939692
= 23.61705mm
Transverse Base Pitch:
= CPt*cos(at)
= 26.019*cos(20.6469)
= 26.019*0.935771
= 24.347mm
CPt (Transverse Circular Pitch)
= (Mn*Pi)/cos(ß)
= (8*Pi)/cos(15)
= (8*3.141592)/0.965925
= 26.019mm
Transverse Pressure
Angle: at
= atan(tan(an)/cos(ß))
= atan(tan(20)/cos(15))
= atan(0.363970/0.965925)
= 20.6469º