The spring calculator can determine spring rates and unit stresses of round wire helical coil compression springs with known parameters. It can also be used to design a spring knowing the working values. This example is based on the following compression spring with closed and ground ends of music wire.
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Determine the required spring rate based on the deflection at a load divided by the difference in the working length and the free length. For this example, the desired spring rate equals 28.8 lb/in (36 lb/1.25 in = 28.8 lb/in).
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2.
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Select Machine Design > Spring Calculator.
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As shown in the above dialog box, select 1 - Outside Dia., Wire Dia., Solid Height from the Method list. After entering the known values, calculate a spring rate close to the desired value by trying several standard wire diameter values. Adjust the material in the Material list to fit the wire diameter used. Here, a wire diameter of .090” gives a spring rate of 26.1 lb/in.
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5.
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As shown in this dialog box, vary the wire diameter and number of active coils to get a spring rate close to the required spring rate. A wire diameter of .095” and 11 active coils gives a spring rate of 28.9 lb/in, but the solid height is 1.235”, which is too high. A wire diameter of .090” and 9 active coils, however, gives a spring rate of 28.4 lb/in, and a solid height of .990”, which is within acceptable limits.
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6.
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Finally, check the stresses applied to the spring to verify that they are within acceptable limits. With a unit stress of 2522 (lb/sq in)/lb, multiply by 36 to obtain 90,792 lb/sq in. With a solid height of .990”, the stress will be:
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