Chapter XX: Appendix: K

GEARS AND GEARINGS

A _spur-gear_ is a gear with teeth cut on its _periphery_, that is an ordinary cog-wheel. _Miter gears_ are two _bevel gears_ of the same diameter which run together. A large miter gear will not mesh with a small miter gear nor with another bevel gear in the proper manner. Miter and bevel gears cannot be interchanged with other sets like spur gears.

All miter gears that you buy ready cut are made so that their shafts run at right angles to each other as shown in Fig. 129, but you can have them cut to order to run at any angle you want.

To find the _pitch_, _pitch diameter_, _circular pitch_, etc., of both spur and bevel gears use these rules:

π = 3.14159
_p_ = pitch
_n_ = number of teeth
_pd_ = pitch diameter
_od_ = outside diameter
_cp_ = circular pitch

_To Find the Pitch_:

n
p = ----
pd

_To Find the Number of Teeth_:

n = p × pd

_To Find the Pitch Diameter_:

n
pd = ---
p

_To Find the Outside Diameter of Spur Wheels_:

(2 + n)
od = -------
p

_To Find the Circular Pitch_:

π
cp = ----
pd

_To Find the Distance Between the Centers of Two Spur Gears_:

(n¹ + n²)
---------
2
---------
p

Where n¹ + n² = the sum of the teeth of both gears.