Machinery's Handbook, 31st Edition
330
Spring Design
.05 inch × Outside diameter
±.05 inch × Outside diameter
5 degrees
.05 inch × Outside diameter
or inch. Whichever is greater 1 64 d 2
45 degrees
Maximum Opening for Closed Loop
Maximum Overlap for Closed Loop
Fig. 18. Maximum Deviations Allowed on Ends and Variation in Alignment of Ends (Loops) for Extension Springs Table 8. Compression Spring Normal Free-Length Tolerances, Squared and Ground Ends
Spring Index
Number of Active Coils per Inch
4
6
8
10
12
14
16
Tolerance, ± Inch per Inch of Free Length a
0.5
0.010 0.011 0.013 0.016 0.019 0.021 0.022 0.023
0.011 0.013 0.015 0.018 0.022 0.024 0.026 0.027
0.012 0.015 0.017 0.021 0.024 0.027 0.029 0.031
0.013 0.016 0.019 0.023 0.026 0.030 0.032 0.034
0.015 0.017 0.020 0.024 0.028 0.032 0.034 0.036
0.016 0.018 0.022 0.026 0.030 0.034 0.036 0.038
0.016 0.019 0.023 0.027 0.032 0.036 0.038
1 2 4 8
12 16 20
0.040 a For springs less than 0.5 inch long, use the tolerances for 0.5 inch long springs. For springs with unground closed ends, multiply the tolerances by 1.7. Courtesy of the Spring Manufacturers Institute Table 9. Extension Spring Normal Free-Length and End Tolerances Free-Length Tolerances End Tolerances Free-Length Tolerances End Tolerances Spring Free Length (inch) Tolerance (inch) Total Number of Coils Angle Between Loop Planes Spring Free Length (inch) Tolerance (inch) Total Number of Coils Angle Between Loop Planes
Up to 0.5
Over 4.0 to 8.0 Over 8.0 to 16.0 Over 16.0 to 24.0
± 0.020
± 0.093 13 to 16
± 60 °
Over 0.5 to 1.0 Over 1.0 to 2.0 Over 2.0 to 4.0
± 0.030 3 to 6 ± 0.040 7 to 9 ± 0.060 10 to 12
± 25 ° ± 35 °
± 0.156 Over 16 Random
± 0.218
± 45 ° Courtesy of the Spring Manufacturers Institute
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