Here is a short tutorial on how to make a camping knife from a old lawnmower blade.
Step 1: Safety
First step is safety, The metal will be hot, the files are abrasive, the spray of sparks is eyeball piercing. Please be safe and use common sense. Personal protection should be worn at all times, even if it's only going to take a second to do or finish. Here is a list of protection I used during this build
1. Safety glasses
2. Leather gloves
3. Face shield when grinding
4. Ear plugs when hammering.
Step 2: Reasons Not to Make This Knife
Lawnmower blades are made to be tough and not shatter when hitting rocks or petrified poop. The metal is of unknown origin and that makes it hard to heat treat and quench. Most modern blades are made of a 1040-1070 steel. To select the best blade I used a grinder to spark test the metal, looking for long sparks that fork out. The burst sparks indicate that the blade has a higher carbon content. Here is a picture from http://modelenginenews.org.
Step 3: Hammering and Annealing
Once a blade is selected I cut it in half to make it easier to handle, some people will use a full blade and incorporate the center mounting holes into their design. To get the blade straight I heated it in a bed of coals until it turned a dull red and hammered it on a piece of rail road track that I use as a anvil. The whole blade will be hot, always assume the blade is hot unless proven cool. Once the blade is straight " enough" I got the coals red hot and heated the blade until it was nonmagnetic, then let the blade cool with the coals overnight. This makes the blade soft and easier to drill and make into a knife shaped object.
Step 4: Shaping the Knife
The blade shape should depend on how you intend to use the knife. Knowing this is a softer steel I choose to make a camping knife, on that is tough but not brittle. Once a shape is picked transfer it to the metal, I used a paint maker. I then drilled along the mark every quarter inch or so to make cutting out the knife easier for me. If you have a band saw then you can just rough out the profile. I used a rotary tool "Dremel" to cut in-between the holes. Save the scraps you will need them later.
Step 5: More Shaping
The blade is starting to look knifey at this point. I used a bench grinder to remove the roughness from the knife, keep the blade moving and don't let it get to hot or it could work harden. If you notice the blade is not as straight as you would like, now it the time to fix that. I used a propane torch to heat the area that needed straightened. Now comes a controversial part. Some say it is best to start the heat treatment now. I wanted to remove as much stock while the metal is still soft. Since the tip will be narrower when finished it will heat up faster in the fire, which can lead to burning causing the metal to decarbon along the cutting edge. Know the risk and weigh the benefits. I did not sharpen the blade yet for this reason and for safety.
To make the cutting edge I used a vise, file attached to pipe with hose clamps, and file jig. The jig keeps the file straight so that the edge is not rounded out.
Step 6: Heat Treating
Not knowing what type of steel this is makes heat treating a guessing game. I heated a piece of scrap till a magnet would not stick to it and quenched it in water. Not knowing the type of steel makes quenching a guessing game. Assuming it is 1050ish means we can use water, brine, or a fast quenching oil. I used water for simplicity but you blade may crack. Old motor oil mixed with ATF can be used but it makes a lot of smoke and it can burst into flames so have a cover ready to put the flames out DO NOT USE WATER ON A OIL FIRE. If the metal has enough carbon in it this will make the metal very hard to file. I then polished the metal so I could watch the color change as I heated it. Using a propane torch I heated the metal to a light brown or straw color and let it air cool, once it starts turning colors be careful because purple and blue are not far behind brown, if it turns other colors it may be to late and you will have to reheat the steel to non magnetic the re-quench. Once cooled I took a file to it to see if it softened it enough. In this case it did so I heated the whole blade to a brown color and then heated the handle to a purple color to make it easier to drill holes for the handle.
Step 7: Handle and Final Sharpening
For the handle I taped two pieces of flat wood to the handle and drill through the blade into the wood so the holes would line up. Then I used some epoxy to glue the handle to the wood and used 1/4 inch aluminum rod as pins. I made the pins 1/8th of a inch longer then the width of the handle and gently pounded them with a hammer to mushroom them out. Then I used a grinder to rough out the handle to fit my hand and a half round file to make finger bumps. As the handle takes shape remember to go slow, it is much easier to remove wood then add it.
To do the final sharpening I used a Lansky sharping kit. depending on what knife you made will depend on the sharpening angle, since this is a beater camping knife I went with a machete inspired 30 degree angle for toughness. This blade is a little soft so it will need to be resharpened often. while this is not the best blade it is a good place to learn for when you start making knives from steel you paid for. Now I'm off to read a instructable on how to take better pictures.