Machinery's Handbook, 31st Edition
344
Spring Design Table 18. Torsion Spring Coil Diameter Tolerances
Spring Index
Wire Diameter, Inch
4
6
8
10
12
14
16
Coil Diameter Tolerance, ± inch
0.015 0.023 0.035 0.051 0.076 0.114 0.172 0.250
0.002 0.002 0.002 0.002 0.003 0.004 0.006 0.008
0.002 0.002 0.002 0.003 0.005 0.007 0.010 0.014
0.002 0.002 0.003 0.005 0.007 0.010 0.013 0.022
0.002 0.003 0.004 0.007 0.009 0.013 0.020 0.030
0.003 0.004 0.006 0.008 0.012 0.018 0.027 0.040
0.003 0.005 0.007 0.010 0.015 0.022 0.034 0.050
0.004 0.006 0.009 0.012 0.018 0.028 0.042
0.060 Miscellaneous Springs.— This section provides information on various springs, some in common use, some less commonly used. Conical compression: These springs taper from top to bottom and are useful where an increasing (instead of a constant) load rate is needed, where solid height must be small, and where vibration must be damped. Conical springs with a uniform pitch are easiest to coil. Load and deflection formulas for compression springs can be used—using the aver- age mean coil diameter, and provided the deflection does not cause the largest active coil to lie against the bottom coil. When this happens, each coil must be calculated separately, using the standard formulas for compression springs. Constant force springs: Those springs are made from flat spring steel and are finding more applications each year. Complicated design procedures can be eliminated by select ing a standard design from thousands now available from several spring manufacturers. Spiral, clock, and motor springs: Although often used in wind-up type motors for toys and other products, these springs are difficult to design and results cannot be calculated with precise accuracy. However, many useful designs have been developed and are avail able from spring manufacturing companies. Flat springs: These springs are often used to overcome operating space limitations in various products such as electric switches and relays. Table 19 lists formulas for design- ing flat springs. The formulas are based on standard beam formulas where the deflection is small. Table 19. Formulas for Flat Springs
P
P
P
P y L
L
L
L
y
y
y
Feature
b 4
Plan
Plan
b
b
b
b
y Ebt PL 4 3 3 =
Et S L 6 b
. . y Ebt PL Et S L 522 087 b 3 3 2 = =
y Ebt PL 3 =
y Ebt PL 3 3 =
Deflection, y Inches
Et S L 4 6 b
3
3 2 b
Et S L
2
2
2
=
=
=
2 4
P L S bt b =
P L S bt =
P L S bt =
2
L Ebt y 6 4 b 2 3 3
2
. L Ebt y 6 522 b 2 3
P L S bt =
6 6 b
Load, P , Pounds
L Ebt y 3 3 3
L Ebt y 3 3
=
=
=
=
3
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