Extension Springs

Extension spring designs generally follow that of compression springs, however consideration must be given to the effects of the end turns.  A wide variety of shapes of end turns are used in the manufacture of extension springs, depending upon the use of the spring.  The most commonly used ends are the single full loop over center shown in the diagram on the right side of the drawing or the half hook over the center as shown in the diagram on the left side of the spring body. Anytime you are trying to add a hook with a sharp turn, there will be considerable stress at the bend. Sometimes it is more advisable to add a hook to the end of an extension spring in the form of an insert. Coned-end designs with swivel bolt or hook inserts can achieve the same results with far less stress then that of machine cut ends. It is advisable to avoid sharp bends in the end hooks, to reduce stress concentration.

Initial tension must be considered when coiling an extension spring. The load may be varied within rather wide limits during the manufacturing process.