Wire springs rank among those technological marvels whose value is immediately recognizable. We find compression, extension, or torsion springs just about everywhere, from screen doors to keyboards. Advances in materials and manufacturing technology have improved springs in the centuries since they were introduced, early in the Industrial Revolution, but the basic idea is the same: spring wire is coiled hot or cold to create an elastic device.
Not all springs are coiled wire, though. There is an alternative in machined springs. They cost more than wire wound springs, but where the application calls for it, machined springs can put unique properties to work.
Although any machinable material including plastics can be used, metal in the form of bar stock is most common the starting point for machined springs. The bar stock is first machined into a thick wall tube form, and then a helical slot is cut revealing multiple coils. When deflected, these coils provide the desired elasticity.
The cost to manufacture machined springs greatly exceeds that of winding wire springs. Wire wound springs can be created with just a few seconds of process time, where a machined spring requires minutes at a minimum. The machines used to create both forms are highly specialized and benefit from computer numerical controls.