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Compression Springs Compression Springs

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Extension Springs Extension Springs

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Torsion Springs Torsion Springs

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Conical Springs Conical Springs

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The Role of Inner Diameter When Selecting Stock Springs

The inner diameter of a coil spring is an important factor when selecting the right stock spring. Whether it is compression, torsion, and sometimes extension spring, knowing the right inner diameter you need will help avoid buying a spring that cannot fulfill the task you need.

 

Compression Spring Inner Diameter

In selecting a compression spring, you need to consider space restrictions based on its installation and surroundings. Some compression springs are placed over a mandrel to provide better stability or keep it in place. If a compression spring's slenderness ratio is too high, it is necessary that it be placed over a shaft or mandrel as it runs the risk of bending or buckling. Determine the size of the mandrel the compression spring will be placed over so you can select an inner diameter that is appropriate to fit over it. Determining the right size inner diameter will also help you avoid friction/scraping between the spring’s coils and the shaft during spring compression. The buckling and friction problems may present themselves as well if the outer diameter of your spring is too snug inside the compartment it is installed into. Therefore, try to be just as vigilant of your spring’s outer diameter and its surroundings.

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Extension Spring Inner Diameter

The weakest point of an extension spring tends to be its hooks, and although some extension springs can withstand great amounts of force, their hooks don’t always keep up. To eliminate this problem, you can replace the hooks with bolts that are threaded into the spring’s inner diameter. The inner diameter of your extension spring is especially important in these cases, because you’ll need to make sure that it's tight enough to hold on to the bolt, yet big enough for the bolt to fit into it.

Whether it is to substitute its hooks for bolts, or you’re using the extension spring to replace worn-out threads in a hole, the threads of the bolt and the wire diameter must also be taken into a note. Since the extension spring’s inner diameter must have a good grip on the bolt (in both cases), the inner diameter must be exactly the same as the outer diameter of the bolt. To calculate the inner diameter and compare it to the screw’s diameter you must subtract two wire diameters from the outer diameter.

 

Inner Diameter = Outer Diameter – 2 Wire Diameters

Dinner=Douter–2d

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Torsion Spring Inner Diameter

The inner diameter of a torsion spring is also important, because it is almost always necessary for a mandrel or shaft to go through it. However, you have an additional factor to consider since a torsion spring’s inner diameter will shrink during deflection. This means that, not only do you need to make sure the inner diameter in its free/unloaded state will fit, but also that it will fit once it has been torqued. This is so that the spring won’t clamp (or bite down) on the shaft and stop it from torquing any further. If the torque is still being applied after your spring’s inner diameter has already bit down on the shaft, you run the risk of damaging your torsion spring. This is due to the fact that the torque will now be applied to the torsion spring’s legs and potentially cause them to break.

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At The Spring Store, it is always our goal to help you find the stock spring that works best for your needs. We are always happy to assist in your search for the ideal spring. This is why we created Spring Finder, so you can easily search and select the spring that best fits your application’s requirements. If you have any additional questions or would like to purchase over the phone you can contact us at: (951) 276-2777.