PITCH CIRCLE (PC): The contact point of mating
gears, the basis of all tooth dimensions, or an imaginary
circle one addendum distance down the tooth
PITCH DIAMETER (PD): The diameter of the
pitch circle. In parallel shaft gears, you can determine
the pitch diameter directly from the center-to-center
distance and the number of teeth.
ROOT CIRCLE (RC): The circle formed by the
bottoms of the gear teeth
ROOT DIAMETER (RD): The distance through
the center of the gear from one side of the root circle to
Figure 14-1.--Cutting specially shaped grooves.
the opposite side
to index the blank, so the teeth are equally spaced and
ADDENDUM (ADD): The height of the part of the
have the correct profile.
tooth that extends outside the pitch circle
CIRCULAR PITCH (CP): The distance from a
SPUR GEAR TERMINOLOGY
point on one tooth to a corresponding point on the next
tooth measured on the pitch circle
The following terms (see fig. 14-2) describe gears
CIRCULAR THICKNESS (CT): One-half of the
and gear teeth. The symbols in parentheses are standard
circular pitch, or the length of the arc between the two
gear nomenclature symbols used and taught at MR
sides of a gear tooth on the pitch circle.
CLEARANCE (CL): The space between the top of
OUTSIDE CIRCLE (OC): The circle formed by the
the tooth of one gear and the bottom of the tooth of its
tops of the gear teeth
OUTSIDE DIAMETER (OD): The diameter to
DEDENDUM (DED): The depth of the tooth inside
which you will turn the blank or the overall diameter of
the pitch circle, or the radial distance between the root
circle and the pitch circle
Figure 14-2.--Gear terminology.