How Do I Harden a Chisel?
Most chisels are made from a grade of steel called "O-1." The metal has been "hardened" and "tempered." Hardening crystallizes steel so it can eventually be worked to a fine edge. But hardening also makes steel difficult to grind, drill or hone and also makes it more likely to fracture. So after steel is hardened, the crystalline structure is usually softened by tempering. If you decide to temper your chisel blade after you harden it, you must reheat the metal to about 500 degrees Fahrenheit -- hotter than the temperature at which paper burns -- and let it cool slowly.
Things You'll Need
- Block magnet
- Needlenose vise grips
- Vise grips
- 5-gallon metal bucket
- 3 gallons motor oil (new or used)
- Flat, stable work surface
- Propane torch
- Butane lighter
- Leather gloves
- Rag
- File
Instructions
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1
Hold the magnet in the needlenose vise grips. Secure the chisel blade in the other vise grips.
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2
Practice plunging the chisel vertically into the empty bucket. If you do not quench this piece of steel vertically, it will warp.
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3
Pour the motor oil into the bucket.
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4
Set the torch on the work surface and ignite its flame with the butane lighter. Adjust the torch flame until it is blue. Put on the gloves.
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5
Heat the end of the chisel blade in the propane flame until the steel glows cherry red.
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6
Touch the magnet to the red-hot steel. When the steel no longer attracts the magnet, the metal has been heated to about 1,450 degrees Fahrenheit and has assumed a pronounced crystalline structure.
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Plunge the red-hot chisel blade vertically into the motor oil. Cooling the steel quickly preserves the crystalline structure. Raise and lower, but do not stir, the chisel blade in the oil until the oil stops bubbling.
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8
Wipe the oil off the chisel. Test the chisel's hardness with the file. You have succeeded if the file will not bite.
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References
- Photo Credit Digital Vision./Digital Vision/Getty Images
