How to Harden & Temper Spring Steel

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Hobbyists of all types often have a need for a small spring. Coil springs are available in variety packs and it is not difficult to find a spring that will work for whatever the application may be. Flat springs are not quite as easy. Because a flat spring can be almost any shape, the hobbyist is unlikely to find a generic spring to fit a specific application. Spring steel is available in flat bars and billets. With a few inexpensive tools, the hobbyist can cut the shape needed, then harden and temper to create a custom spring.

Things You'll Need

  • Spring steel
  • Hacksaw
  • Rotary tool with cutoff wheel, felt polishing bob and polishing rouge
  • Mapp torch
  • Pliers
  • Small anvil
  • Ballpeen hammer
  • Steel can
  • Motor oil
  • Magnet
  • Small steel baking pan

Form the Spring

  • Cut a rough approximation of the spring out of the steel. Use the hacksaw and cutoff wheel to get the shape close, but leave it slightly oversize.

  • Heat the spring blank to bright red. Use the pliers to hold it on the anvil and tap it to its final shape with the hammer.

  • Allow the spring to cool. Use the cutoff wheel to trim it to length. Polish it with the felt bob and rouge.

Harden the Spring

  • Fill the can about three-quarters full with oil. Hold the spring with the pliers and heat it until it will no longer stick to the magnet.

  • Quench the hot spring in the oil. Keep the spring moving in the oil until it is cool. If the oil catches fire, set the pan on the can to put the fire out.

Tempering the Spring

  • Set the pan on a heatproof surface. Lay the spring in the pan.

  • Pour oil into the pan until it covers the spring.

  • Use the torch to ignite the oil in the pan. Allow the oil to burn until it is depleted. When the spring cools, it is ready to use.

Tips & Warnings

  • Keep your hands and face away from the can when you quench the spring. Perform this task outdoors in a non-flammable environment. Keep a fire extinguisher handy when heat treating metals. Always wear safety glasses and gloves when working with metal.

References

  • Photo Credit John Foxx/Stockbyte/Getty Images
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