Machinery's Handbook, 31st Edition
2634
Transmission Roller Chains Table 12. Standard Hob Design for Roller Chain Sprockets
D s
E
F
17 ° 1 2
F ”
H
C
35°
R O R
Y
X
U
T
K
K ”
J
J ”
G
G
Q
Q
90°
P n
Section Normal to Hob Teeth Data for Laying Out Hob Outlines — Inches
No. Gashes
O.D.
Bore 1.250 1.250 1.250 1.250 1.250 1.250 1.250 1.250 1.500 1.500 1.750 1.750 2.000
Keyway 1 ∕ 4 × 1 ∕ 8 1 ∕ 4 × 1 ∕ 8 1 ∕ 4 × 1 ∕ 8 11 ∕ 4 × 1 ∕ 8 1 ∕ 4 × 1 ∕ 8 1 ∕ 4 × 1 ∕ 8 1 ∕ 4 × 1 ∕ 8 1 ∕ 4 × 1 ∕ 8 3 ∕ 8 × 3 ∕ 16 3 ∕ 8 × 3 ∕ 16 3 ∕ 8 × 3 ∕ 16 3 ∕ 8 × 3 ∕ 16
P
P n
H
E
W
0.2527 0.379 0.506 0.632 0.759 1.011 1.264 1.517 1.770 2.022 2.275 2.528
0.0675 0.101 0.135 0.170 0.202 0.270 0.337 0.405 0.472 0.540 0.607 0.675 0.810
0.0075 0.012 0.015 0.018 0.023 0.030 0.038 0.045 0.053 0.060 0.068 0.075 0.090
13 13 12 12 11 11 10 10
2 1 ∕ 2 2 1 ∕ 2 2 1 ∕ 2 2 1 ∕ 2 2 7 ∕ 8 3 3 ∕ 4 4 1 ∕ 2 5 1 ∕ 4 6 3 ∕ 4 8 1 ∕ 2 9 3 ∕ 8 6
2 5 ∕ 8 3 1 ∕ 8 3 3 ∕ 8 3 5 ∕ 8 3 3 ∕ 4 4 3 ∕ 8 4 3 ∕ 4 5 3 ∕ 8 6 3 ∕ 8 6 7 ∕ 8 8 5 ∕ 8 9 3 ∕ 4 8
1 ∕ 4 3 ∕ 8 1 ∕ 2 5 ∕ 8 3 ∕ 4
1
1 1 ∕ 4 1 1 ∕ 2 1 3 ∕ 4 2 1 ∕ 4 2 1 ∕ 2 2
9 9 8 8
3
3.033 8 Hobs designed for a given roller diameter ( D r ) and chain pitch ( P ) will cut any number of teeth. P = Pitch of Chain P n = Normal Pitch of Hob = 1.011 P inches D s = Minimum Diameter of Seating Curve = 1.005 D r + 0.003 inches 11 1 ∕ 4 1 ∕ 2 × 3 ∕ 6
F = Radius Center for Arc GK ; TO = OU = P n ÷ 2 H = 0.27 P E = 0.03 P = Radius of Fillet Circle
Q is located on line passing through F and J . Point J is intersection of line XY with circle of di- ameter D s . R is found by trial and the arc of this radius is tangent to arc K G at K and to fillet radius. OD = Outside Diameter = 1.7(Bore + D r + 0.7 P ) approx. D h = Pitch Diameter = OD − D s ; M = HelixAngle; sin M = P n ÷ π D h L = Lead = P n ÷ cos M ; W = Width = Not less than 2 × Bore, or 6 D r , or 3.2 P To the length obtained by this formula, add enough to make a whole number (and for a roller chain, an even number) of pitches. If a roller chain has an odd number of pitches, it will be necessary to use an offset connecting link. Another formula for obtaining chain length in which D = distance between centers of shafts; R = pitch radius of large sprocket; r = pitch radius of small sprocket: N = number of teeth in large sprocket; n = number of teeth in small sprocket; P = pitch of chain and sprockets; and l = required chain length in inches, is: cos sin l NP nP D D R r 360 180 2 360 180 2 2 where ° ° ° ° α α α α = + + − + = −
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