How to Forge a Knife & Temper It

Forging and Annealing

• 1

  To forge a knife, you first need a billet of steel. There are a number of excellent steel choices, from recycled chains to old springs, to ordering complete billets online. A great piece of steel with which to start your first knife is a metal file. They are easy to find locally and are inexpensive.

• 2

  Using gloves, a welding visor and tongs, feed the steel into the forge. A simple coal forge can be heated by increasing air flow to the fire, whereas a complex gas forge will have temperature gauges and heat controls. Slowly heat the steel until it begins to glow, before increasing the heat until the steel is red hot.

• 3

  Continue to hammer out and reheat the steel to your desired shape. Evenly flatten out the steel down its entire length. If you overheat the tip and then try to heat the tang, the tip will be too cool when the tang is the correct temperature.

• 4

  Once the forging is done, anneal the steel by letting it cool slowly. A simple method to achieve this is to bury the blade in a pile of dirt, letting it cool completely before removing it. Once the blade is cool to the touch, putting it in the freezer overnight helps to stabilize the steel. Repeat this process twice more over two more days. As opposed to using the forge for this, you can make a small campfire and place the blade in it. Once the fire burns itself out, bury the blade with dirt and ash and allow it to cool.

Shaping and Hardening

• 5

  Using a hand file, file the annealed steel to your desired shape. The metal will be soft now and should be easy to work with. Flatten both sides of the blade and clean up the spine. Define the tip of your blade and add the taper down to the edge.

• 6

  Reheat the blade to a glowing orange, slowly increasing the temperature above the red color range. Use a magnet to touch the metal. When the magnet no longer sticks, it is ready to be quenched. This step must be done quickly for the proper heat treatment.

• 7

  With the shaped steel still in your tongs, dunk the entire blade, edge first, into the quench tank. Different steel types need different quenching mediums including water, oil or brine water. The steel file should be quenched in oil. There are specialty quenching oils available, but for a first try, a thin motor oil will work. Hardening the entire blade is a process called "through-hardening." Hold the blade in the oil until the bubbles and the steam stop.

• 8

  Once the blade is quenched, leave it in the quench tank until both oil and blade reach room temperature. You can test the hardening with a hand file, to see whether the file bites into the steel. If it does, the blade is too soft and must be rehardened. If the file glances off, the blade is hardened, and ready for tempering.

• 9

  Once the blade is hardened, grip it with your tongs once more and heat it from the spine. Allow the spine of the blade to heat to yellow evenly, from the back of the tip down the entire spine. This tempering will grant the blade flexibility, making it less brittle.

Polishing and Mounting

• 10

  For a simple wooden handle, drill a hole through a 1-inch dowel rod, slightly smaller than the tang. Heat the tang one last time and use it to burn the hole in the dowel. This will ensure a perfect fit quickly. Finish the wood with sanding and stains to your personal taste.

• 11

  Starting with a coarse, 200-grit sandpaper, begin polishing off the oxidation and pushing the steel into shape. The polishing stage will present the final shape of the blade, so be sure to use careful strokes. Slide the sandpaper down from the spine to the bevel, and then start a new stroke from the bevel to the edge. Apply even pressure and slowly begin to coax the final shape of the blade.

• 12

  Move up to 400-grit sandpaper and continue the process. At these low grits, it is easy to do too much sanding; starting over requires returning to a lower grit and resurfacing. At 800 grit, begin to rotate your strokes 90 degrees and cover the blade long-ways until the 400-grit marks are gone. Then alternate again with 1,000 grit until the 800-grit marks are gone. Sanding the metal in this fashion toward the edge should thin the metal to a razor edge. Additional sharpening should not be needed.