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GEAR TEETH. 375
GEAR TEETH.
Circular Pitch.
The length of the pitch circle or pitch line from center of
one tooth to the center of the next is the circular pitch of a gear,
or a rack.
Cast gear teeth, constructed on the circular pitch system,
may be made of the following proportions
:
Thickness of tooth on pitch line = T
6
f pitch.
Space between teeth on pitch line == T
7
¥ pitch.
Height of tooth outside of the pitch line = T
3
o pitch.
Depth of space inside of pitch line = T% pitch.
-..^ ... £ circular pitch X number of teeth.
Pitch diameter of gear =
3.1416
For cut gears, use the following formulas
:
Thickness of tooth on pitch line = 0.5 pitch.
Space between teeth on pitch line = 0.5 pitch.
Height of tooth outside pitch line = 0.3183 pitch.
Depth of space inside of pitch line == 0.3683 pitch.
To Calculate Diameter of Gear According to Circular Pitch.
Rule.
Multiply the circular pitch by the number of teeth in
the gear and divide the product by 3.1416 ; the quotient is
the diameter of the pitch circle ; add j% of the circular pitch to
obtain the whole diameter of the gear.
Example.
Find whole diameter of a gear of 48 teeth and three-inch
circular pitch.
Solution
:
O \/ AQ
Pitch diameter = . . . .
_
= 45.84 inches.
3.141b
Double the addendum = 3X0.6= 1.80
The whole diameter is 47.64 inches.
Table No. 47 is calculated for one-inch circular pitch ; to
find the pitch diameter of a gear of any number of teeth given
in the table, multiply the diameter given in the table by the
circular pitch in the gear, and the product is the pitch diameter
of the gear. In order to find the whole diameter, add twice the
height of the tooth outside the pitch line, as calculated by the
above formula.
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