Machinery's Handbook, 31st Edition
Spring Design
343
Table 15. Correction Factors for Other Materials
Material a
Factor
Material a
Factor
Hard Drawn MB Chrome-vanadium Chrome-silicon Stainless 302 and 304
0.75 Stainless 316 1.10 Up to 1 ∕
0.75 0.65 0.65 1.00 1.07 1.12
8 inch diameter
1.20 Over 1 ∕
8 to
1 ∕ 4 inch diameter
4 inch diameter
Over 1 ∕
0.85 Stainless 17-7 PH
Up to 1 ∕ Over 1 ∕ Over 1 ∕
8 inch diameter
0.75 Up to
8 to
1 ∕ 4 inch diameter
1 ∕ 8 inch diameter
0.65 Over
4 inch diameter
8 to
3 ∕ 16 inch diameter
1 ∕
0.80 Over 3 ∕
Stainless 431 Stainless 420
16 inch diameter
0.85 … a For use with values in Table 14. Note: The figures in Table 14 are for music wire (ASTM A228) and oil-tempered MB grade (ASTM A229) and can be used for several other materials that have a similar modulus of elasticity E . However, the design stress may be too high or too low, and therefore the design stress, torque, and deflection per coil should each be multiplied by the appropriate correction factor when using any of the materials given in this table (Table 15). … Torsion Spring Tolerances.— Torsion springs are coiled in a different manner from other types of coiled springs and therefore different tolerances apply. The commercial tolerance on loads is ± 10 percent and is specified with reference to the angular deflection. For example: 100 pound-inches ± 10 percent at 45 degrees deflection. One load specified usually suffices. If two loads and two deflections are specified, the manufacturing and testing times are increased. Tolerances smaller than ± 10 percent require each spring to be individually tested and adjusted, which adds considerably to manufacturing time and cost. Table 16, Table 17, and Table 18 give, respectively, free angle tolerances, tolerances on the number of coils, and coil diameter tolerances. Table 16. Torsion Spring Tolerances for Angular Relationship of Ends
Spring Index
Number of Coils ( N )
4
6
8
10
12
14
16
18
20
Free Angle Tolerance, ± degrees
1 2 3 4 5 6 8
2 4 7 8
3 5 7 9
3.5
4 7
4.5
5
5.5
5.5 9.5
6
6 8
8
8.5
9
10 14 17 21 24 29 34 42 51 63 70
5.5
9.5
10.5
11 15 18 25 29 36 44 52 60 84
12 16 20 21 27 38 47 56 65 90
13
10 12 18 21 28 34 40 44 63
12 14 16 24 31 37 44 50 70
14 16 19 23 27 34 41 48 55 77
16.5 20.5 22.5
10 12 15 19 25 30 35 38 55
9.5
14.5
20.5
12 14 20 25 29 32 45
20.5
28
10 15 20 25 30 50
31.5
32.5
40 49 60 68 95
100
Table 17. Torsion Spring Tolerance on Number of Coils
Number of Coils
Tolerance
Number of Coils
Tolerance
up to 5
over 10 to 20 over 20 to 40
± 5 °
± 15 ° ± 30 °
over 5 to 10
± 10 °
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