All About Variable Diameter Springs

The majority of springs in operation today are linear springs, meaning that the force required to push or pull them out of a resting state increases linearly with the amount of deformation. Going back to Hooke’s Law, linear springs’ forces can be mapped with the equation F=kX, with k being the spring constant and X being the length of deformation. Variable diameter springs are a category of springs that often don’t follow these rules. This in itself can be advantageous to manufacturers in certain cases, but a number of other properties make variable diameter springs necessary for a range of products. Their potential advantages include:

  • Adjustability of force required to compress the spring
  • Increase in travel because one coil can fit into the other
  • Decrease in “solid height,” or height of the spring at full compression
  • Greater lateral stability for longer springs

Variable diameter springs include conical springs, hourglass springs and barrel springs.

  • Conical springs are wider at one end than the other, and are also known as tapered springs.
  • Hourglass springs, or concave springs, are wider at both ends and narrower in the middle.
  • Barrel springs, or convex springs, are wider in the middle and narrower on both ends.
Examples of Products Using Variable Diameter Springs
  • Battery compartments
    Open your remote control and you’ll most likely find a number of battery compartments with coiled springs at one end. Conical springs are often used in small spaces like this, because they can compress down to the height of their wire diameter.
  • Firearm Triggering Mechanisms
    Because of their ability to modulate force and avoid buckling, conical and barrel springs can offer more precise control over triggering mechanisms.
  • High-End Mattresses
    Mattresses advertising “pocket coils” often utilize individually wrapped barrel springs to provide support to sleepers. Other mattresses utilize hourglass springs, which are intended to flex laterally to provide support from any angle.
  • Automotive Suspension
    Barrel springs, hourglass springs and conical springs are often used in automotive suspension systems, both because of their ability to compress without buckling and increase travel through coil telescoping.
Manufacturing Variable Diameter Springs

Variable Diameter Springs from Automated Industrial MotionSkilled spring manufacturers using advanced coiling equipment can produce variable diameter springs of nearly limitless complexity, even combining characteristics of conical, hourglass and barrel springs into a single coil. In calculating characteristics like spring rate, spring manufacturers must treat each individual coil as a separate spring.

In addition to compression-spring variables like wire diameter and end treatment, manufacturers of variable diameter springs must also consider:

  • Spring rate: should the spring approximate linear force, constant force or otherwise variable force?
  • Spring pitch: should spring pitch be constant, or vary along with the diameter?
  • Telescoping: does one coil need to fit into the next, and how much clearance is required?
  • Linear deflection: how much barreling is required to prevent buckling?

CNC spring coilers are highly advantageous in manufacturing variable diameter springs. By keying in the starting diameter, middle diameter and end diameter, the operator can dependably produce thousands of springs with a high degree of precision. AIM’s line of CNC spring coilers can be configured to manufacture compression springs with nearly any sequence of diameters.

Learn More

Take a look at these resources for more information on the springs and spring coilers discussed in this blog.

Posts in our “All About Springs” series