Introduction: Making a Kitchen Knife From a Machete
In this Instructable I make a kitchen knife. Now the metal I chose to use was from an inexpensive machete. It was easy to get locally, typically high carbon steel that can be used for making knives you need to mail order for it and in Canada is it costly unless you place a large order.
The metal in a machete contains enough carbon that it can be hardened to produce a blade that will retain it sharpness. The way to test to see if piece of steel can be hardened is to heat it until it becomes non-magnetic or red-hot and then quench in oil or water. Then once cool, rub a file over the steel, if the file glides over the surface the metal was hardened.
This is all a learning process for me so I'm just sharing my experience!
Step 1: Video
Here is the video from start to finish of making the knife, it's how I was able to make a knife with the skills, tools and techniques I know. I'm sure there are better ways but this is all a learning a process so don't take this a perfect guide, I'm just sharing my experience of the process. The written steps follow.
Step 2: Materials Used and Tools
- Machete or some other source of high carbon steel
- Hardwood(s) for handle
- Vegetable oil for heat treating
- Belt Grinder
- Mini Grinder with cutting disc
- Blow Torch
- Propane Forge or Charcoal BBQ
- Tongs or long pliers
- Sharpening Stones
- Wet/dry sandpaper
Step 3: Annealing
Depending on what ever metal you use, it is best to anneal it so it can be worked. Annealing is the process of removing the hardness from the metal. It really is simple to do, just head up the metal with a torch until red hot and then let cool slowly, do not quench the metal.
Step 4: Cutting Out the Knife Blank
First step is to pick a knife shape, I chose a Japanese Santoku style knife shape. I made an outline on a piece of paper and then transferred it to the metal. Using a metal cutting disc on a mini grinder the knife blank was cut out.
This knife is only similar in shape to a Japanese kitchen knife, the metals used in Japanese knife are far different and the techniques to make one are very different. Typically Japanese kitchen knives have a high carbon core for the edge, sandwiched between a softer jacket metal.
Step 5: Rough Grinding
Next using a small belt grinder, the bulk of the material was removed. Grinding with the edge upward, the steel was removed using a rough grit belt (60 or 80), the knife has a flat grind. A flat grind is exactly as it sounds the top of the knife to the bottom edge is ground with a flat taper on both sides. Once a profile was ground, the edge was left around 0.25mm thick as heat treating will cause the blade to warp and leaving it thicker will help keep it from warping too much.
Step 6: Heat Treating
Heat treating to harden the steel was accomplished by heating the blade to a critical temperature to the point where a magnet will not stick to it and then rapidly quenching the blade in oil. I did not use a magnet but I did some testing with some of the scrap and established a color that I will heat the metal up to and then quench to harden.
You need to harden the metal so it will retain an edge, otherwise it will sharpen but dull quickly or not hold an edge at all.
A propane forge was used to do this but you can do this also with a hot fire. Build a fire with charcoal and blow air into the fire with a hairdryer through a metal pipe. The air will cause a hot spot in the fire so you will need to keep moving the blade in and out of the hot spot or use it could burn or even melt the metal. Once up to critical temperature quench in oil.
The oil used was cooking oil, you can use other oils but vegetables oils seem less toxic.
Step 7: Tempering
After heat treating the metal should be really hard and brittle and while this is good for razors it isn't good for kitchen knives or durability.
You can test that the metal hardened successfully by running the edge of a file over the steel, it should just skate over the metal. If it doesn't then that means either the steel won't harden or something went wrong during the hardening stage.
I like cleaning the blade off before tempering and this was accomplished by soaking in vinegar overnight to remove the fire scale. Grinding is also acceptable too.
So the knife needs to be tempered to soften the metal down. This can be done in the forge by judging the color of the steel but it is much easier to throw it in the kitchen oven at 425f for an hour. Also note that kitchen oven thermometers are not very accurate so it's best to get an external one.
I used a laser thermometer was used to check the temperature every so often.
Step 8: Final Grinding and Sanding
The knife was lightly finished on the belt grinder again with a 80 grit belt to remove additional metal and then up to a 120 grit belt. At this point the blade should almost have an edge forming as this knife is a flat grind meaning it is thick on the top and thin to the edge on the bottom with no bevels.
Once I was happy with the profile, the knife was wet sanded with 220, 400 and upward if you want to have a really polished knife. Wet sanding was done by having the sand paper on a board and rubbing the knife back and forth on it, going only in one direction, adding water occasionally to flush away the removed metal.
I made a mistake grinding during rough grinding so some of the earlier scratches were hard to remove as I removed a little too much metal on the top of the blade. But overall it was ok.
Step 9: Making a Handle
To make a handle I chose to use a maple wood as I like the light color and is not too hard to work with. I may try on future knives using an exotic hardwood. I cut out a rectangle block of wood that I thought would fit my hand. Then the edges were rounded with a quarter round router bit. Simple but effective and nice to hold in the hand.
Fitting the knife into the handle was accomplished by drilling out the handle and then to get a solid fit, heating the knife tang to red hot and inserting it into the hole. The burning off the wood made the handle fit nice and tight but glue will be used later to ensure a solid hold.
A covering plate was made using a piece of thin stainless steel I had laying around. A slot was cut into it using a rotary tool with a small cutting disc, then it was cut out a little larger than handle. This plate servers two purposes, it hides the hole where the tang meets the wood and it looks nice.
Step 10: Gluing the Handle
Everything was held together using some clear 5 minute epoxy, epoxy was placed into the hole of the knife and glue was applied to the covering plate. Then all the parts were inserted together and left to cure.
Once cured the stainless covering and glue were ground off to make it flush with the wooden handle, go slow as making a mistake here after all the hard work would be hard to fix. Some final hand sanding was done to finish the handle.
Step 11: Sharpening
An rough edge was put on the knife using the belt grinder with a 220 belt. At this point the knife will cut but we want this knife really sharp so the final sharpening will be done with a Japanese water stone. This water stone has two sides a 1000 grit and the other side has a 4000 grit. Using lots of water the edge of the knife was rubbed back and forth, count the strokes you do on one side and then repeat on the other. Work the whole edge of the knife in sections.
Then to finish the sharping starting you want to "strop" the knife from tip to heel of the edge, do this many times or as many times as you want until you obtain the sharpness you want.
Step 12: Finished Knife and Care
The knife is now finished, overall it came out well with a few mistakes but it certainly is usable in the kitchen. Since this is a carbon steel knife with a natural wooden handle, it has to be cared for after use, ensuring to dry it before putting it away or it will rust. Over time the blade will form a nice patina that will keep it from rusting and will make it much easier to care for. The patina is magnetite also called mill scale a tough oxide of iron and forms over time but unlike rust it won't taint the food.
So to summarize care for a carbon knife is wipe clean after each use and put it away, you can wipe some vegetable oil for some additional protection until the patina forms but is optional.