Intro: Tempering a Knife Using My Coffee Can Forge.
This is an update to my coffee can forge. I have been using it to heat treat knives I have made. I am not an expert at this and do not pretend to be.
When using heat and metal it is always a good Idea to have a fire extinguisher handy. Use heat resistant gloves and be safe.
Forge (build your own here: https://www.instructables.com/id/Coffee-Can-Forge/ )
Oil / fire resistant container
Step 1: Apply Heat
- Again I am not an expert at this so...... Don't get too bent out of shape if I'm not using proper methods. I recommend checking out https://www.instructables.com/id/Heat-Treating-Kni... for more detailed instructions and better techniques.
Step 1 is to heat up the oil we will be using for our quench. After doing some research this allows for an even cooling and helps to prevent bad stuff happening to the metal. Think boiling hot water on a car window in the middle of winter.
Step 2 is firing up the forge and heating up your knife as well as the scrap piece you will be using to warm up your quench oil. (Just warm oil is fine. 95 degrees or so.)
Step 3 The metal you are heat treating needs to be hot enough to lose its magnetic attraction. You test this by putting a magnet near it.
Remember that HOT STUFF IS HOT!!!
Step 2: Quenching
More sciency stuff
Okay, Now it is time for quenching. There are different schools of thought about which method is the best to prevent the most cracking and warping. There is edge first, Spine first, and point to handle. I think that the Leidenfrost effect is enough of a barrier to allow the entire piece to enter the quench media before cooling really begins in earnest. Also I'm a bit lazy and don't want to do the extra prep to use the other methods so I just quench point first. True story!
**Important safety tip: When quenching, the oil may catch fire. Use a flame resistant cover to smother the flames.
Step 1 after you have heated the oil up dip your demagnetized knife into the oil using some channel locks or pliers. Allow it to cool there for a bit before putting it on a paper towel to dry off and remove the excess oil.
Step 3: Tempering
You metal is now in an extremely delicate state now. I warn you do not drop it or it could cause fractures that will weaken the metal severely. It could also break into many large pieces.
While it is brittle it is also very hard. It should now pass a file test. slide a file across the metal surface. It shouldn't want to grab or catch the metal surface like normal. This test is pretty standard for whether or not the metal has properly quenched.
If it hasn't properly quenched, clean the knife very well and reheat it to try quenching a second time.
In order to properly maintain strength and flexibility, you must temper the metal. This is a really easy step. Heat the knife up to 400 F for 1 hour and then let cool to room temperature on its own.
Repeat this step two more times. And you are done. The blade should be properly heat treated and ready for work.