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NOMENCLATURE
A = Outside to outside of flat of teeth measured across sprocket.
a = Inside to inside of flat of teeth measured across sprocket
B = Outside to outside of flat of perforations, green film.
B' = Outside to outside of flat of perforations, shrunk film.
b = Inside to inside of flat of perforations, green film.
b' = Inside to inside of flat of perforations, shrunk film.
D = Pitch diameter of sprocket. (See Note No. 1)
D' = Base diameter of sprocket.
G = Gauge (transverse) of perforations, green film.
G' = Gauge (transverse) of perforations, shrunk film.
K = Thickness of the film. (See note No. 2)
L = Length of flat of perforations, green film.
L' = Length of flat of perforations, shrunk film.
N = Number of teeth in sprocket.
N' = Maximum number of teeth of sprocket that may engage film.
P = Perforated pitch (longitudinal) of green film.
P' = Pitch of perforations, shrunk film.
P"= Pitch of sprocket teeth (circular). See Note No. 3.
S = Shrinkage per unit length (longitudinal).
T = Transverse shrinkage per unit width.
t = Thickness of sprocket tooth at root.
w = Width of perforation, green film.
Pi =3.1416
Note No. 1
The pitch diameter of a sprocket is the diameter of an imaginary circle coinciding with the center line or neutral axis of the film, when in contact with the base diameter of the sprocket, and is, therefore, equal to the base diameter plus the thickness of the film.
Note No. 2
Twice the thickness of that section of the film between the pitch line and the base diameter of sprocket. When based on the assumption that the center line of the film is the neutral axis, K equals thickness of film.
Note No. 3
The circular pitch of the sprocket teeth is the distance from center to center (or from flank to flank) of the teeth measured along the arc of a circle coinciding with the center line or neutral axis of the film when in contact with the base diameter of the sprocket. Circular pitch therefore is equal to a tooth and a space, measured on the pitch circle.
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