PRECISION MEASURING AND GAGING - OD1642 --LESSON 1/TASK 2
(2) In order to understand measurements made with the gear tooth
vernier, the machinist should know gear tooth terminology.
The following
terms (figure 52 on page 81) are used to describe gear and gear teeth
(symbols in parentheses are standard gear nomenclature symbols).
(a) Outside Circle (OC): The circle formed by the tops of the gear
teeth.
FIGURE 50.
USING BEVEL PROTRACTOR.
(b) Outside Diameter (OD): The diameter the gear blank is machined
to; the overall diameter of the gear.
(c) Pitch Circle (PC): (1) Contact point of the mating gears,
basis of all tooth dimensions. (2) Imaginary circle one addendum distance
down the tooth.
(d) Pitch Diameter (PD): (1) The diameter of the pitch circle.
(2) In parallel shaft gears, the pitch diameter can be determined directly
from the center to center distance and the number of teeth.
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