I decided that I was going to make myself a knife from a file. There are many guides on the Internet that tell you how to do this, but this one will be mine. This part of the guide is going to explain the process that I used to design and make the blade from start to finish in great detail, unlike the other guides that are out there that say something vague like “quench” and “heat treat at 425”.
The first thing you should do is decide what you are going to do with your knife, and exactly how it is going to look. I only did the first bit, and sorely regretted it later. Since you are going to make the knife from a file, I would suggest going out and buying one. I used a 6″ Nicholson bastard file, which was about $5 at OSH. I based on what I have read on the web and knife making forums, Nicholson files are W1 (W-1?) steel, which is water or brine hardening. Beware the dollar store file! Some of them are not high carbon steel, but low carbon steel that has been case hardened. You wouldn’t want to waste days of work just to have a soft knife, would you?
Trace the file out on a piece of paper. Hold the file in your hand and figure out how big of a handle you want. Decide if you want a depression for your index finger or thumb. Think about the work the blade will be doing, and how long you have to finish the blade, and what your skill level is with the medium. I have a lot of experience filing things, but none with forging or heat treating, so I went with a thick, durable blade, with a slightly finer edge for slicing, scalpel-style. It should be good for cutting up fruit and opening boxes, which is what I normally use my (current) knife for. I also wanted to try to use some mosaic pins, and this got me in trouble because I did not take them into account in my design.
Once you settle on a design, you will need to anneal the file before you can start to remove the material. Remember, you never want to rub your files on each other because they will get dull. This is because the metal is incredibly hard. Annealing softens the metal so that you can grind/file it off more easily. The way to anneal steel is to heat it up and let it cool VERY SLOWLY. How hot it gets and how long you it cool play into how soft it gets. I heated mine up to a dull red hot and let it cool in air, and it was soft enough for me to work with. You can also just leave it in your forge and let it forge-cool, but you will have to wait until long after all your charcoal goes out before you can touch it.
Here I have used the grinder to do some stock removal. It is best to keep the steel cool during this process by dipping it in water. As you can see, the blade got very hot during this grinding process, causing some tempering colors to begin to appear on the blade. It got so hot that some parts hardened when I dipped it in water to cool it off! I used a butane torch to heat it up and anneal it again once I started to file. You can tell the bevel is very uneven right now, because there are several facets that have light reflecting off of them. This can be a good way to file straight; just file until the whole blade is reflecting light at the same time, or not. While filing, you should be able to see the color of light and the finish of that particular facet spread across the blade.
Here is another shot of the filing process. It is best to keep your knife locked down so you can file the bevels flat. Here I have C-clamped the knife to a piece of wood, and put the wood in the vice, making it very easy to file the knife without it moving. You can also see a sharpie line I drew on the annealed blank- this is so I do not remove material past the line, in order to create the correct shape of bevel. The sharpie that is on the blade is to check for high spots. I color the whole thing in, and then take a piece of sandpaper stapled to a piece of flat wood, and push it over the blade. High spots (relative to their surroundings) end up polished, and low spots end up still covered in ink. You can see this effect in the scratches on the blade, and the edge where the bevel begins, which is relatively higher than the neighboring portions of the blade. I wanted a thick blade, because I want this knife to be tough. I was going to have only one bevel on one side, and two on the other so that it would be easy to sharpen for me, as a righty. This was a mistake, as it turns out, because the single-bevel side always gets scratched by the sharpening stone. Oh well, you live and you learn.
This is also a great time to drill holes for your bolster and handle pins! I drilled 1/4″ holes with a hand-held drill. Hopefully I did them straight-ish. A drill press is really handy here, but I don’t have one at home.
The next step is to normalize the steel. You do this by heating the blade to non-magnetic and then letting it air cool. If we had been beating on it with a hammer, this would help reduce the stress in the blade. Since I didn’t actually beat on it to form the blade, I am hoping this takes care of any stress caused by heating during grinding or drilling. It does not take too long, and it seems like a good precaution. Some people normalize up to three times, but I thought two cycles would be just fine given that I did not pound on the blade.
The next step is to harden, and then temper the blade. This process is collectively called heat treating. There is a lot of conflicting information about how to do it properly. The most consistent message I found was to quench in brine, water, or oil, and then stick it in the oven at somewhere between 425-475 F for about an hour, depending on how hard you want your blade to be in the end.
This leaves a lot to be desired. I found a lot of believable information about the process here, but their process is very specific and it was hard for me to estimate what temperature my blade was. The process I used was to heat to non-magnetic, quench in brine (recipe: add salt to water until it will not dissolve anymore) using a slicing motion and then polish a small portion of the now forge-scaled and tempered blade. This was done to make the temper colors visible when I stuck it in the oven at 450 F. I waited until the edge of the blade to turn a “light straw” color, and pulled it out and let it air cool. Mine might have been a little dark, but better over-baked than over-melted!
After a little sanding, The blade was looking much better. It is super effective against fruits, vegetables, and paper, and it even looked a little bit like the knife I planned on making. After some more polishing, It will receive an nice handle and a bolster of undetermined material, and a couple mosaic pins.