BEVEL AND MITER GEARS–THE SIZE SYSTEM
Miter and bevel gears are listed in your catalog according to their diametral pitch, a term you should be familiar with by now. As you will recall, the diametral pitch (also referred to as pitch) indicates the size of a gear tooth.
On miter and bevel gears, that tooth size is measured on the large end of the tooth. (See Figure 5.2)
Important: Both gears in a miter or bevel gear set must be of the same pitch.
The following formula is used to determine diametral pitch.
Pitch (D.P.) = Number of Teeth ÷ Pitch Diameter
This concept is reviewed below. (See Figure 5.2A)
CIRCULAR PITCH
On spur, helical and worm gears, we learned how to calculate circular pitch. Now let’s see how the circular pitch of bevel and miter gears are calculated.
Circular pitch (p) is the distance – along the pitch line or circle
– from any point on a gear tooth to the corresponding point on the next tooth. It is also equal to the circumference of the pitch circle divided by the number of teeth. (See Figure 5.2B)
The formula for determining circular pitch (p) follows:
• p = πd (where d (or D) = the pitch diameter) ÷ n
(where n (or N) = the number of teeth)
Example: To determine the circular pitch (p) of a 48-tooth gear (n) with an 8-inch pitch diameter (d):
p = 3.1416 x 8 ÷ 48 = 25.1328 ÷ 48 = .5236 inches
Note: Gears of larger circular pitch have larger teeth than gears of smaller circular pitch.
