From File To Knife: Make a Bushcraft Knife Using Simple Tools

-Old file
-Piece of hardwood
-Two-part epoxy adhesive
-Coal
-Forge (something to burn the coal in)
-Air pump
-Tongs
-Quenching oil
-Kitchen oven
-Scriber, permanent marker
-Caliper
-Vice
-Clamps
-Hacksaw
-Lubricating oil
-Files
-Sandpaper
-Drill
-Hammer

Step 2: Finding the Right File

The first thing to realize is that “steel” is a generic term for alloys of iron and other elements. So steel comes in various compositions that are important to understand before you begin knife-making.

Not only the composition of a type of steel determines its properties like hardness, ductility and tensile strength, though. The way the alloying elements are arranged on a microscopic level also influence material properties. So, steels with the same composition may have different material properties, depending upon the microstructure of the steel. And the microstructure can be changed by heat treatment or cold deformation. In order for a knife to hold an edge, it needs to be hard. Among other elements, carbon is added to make steel capable of being hardened. So, what you need for a knife is steel with high carbon content.

Old files, as well as leaf springs and old sawmill blades, are made of high carbon steel. Most new files are case-hardened, which means that only the outer layer is high-carbon steel while the core is mild steel. Try to get find an old file to make your bushcraft knife.

There are a few ways to verify whether you’re dealing with the right file:

Spark test: If you have a grinder, see if the steel on the surface of the file — and the steel 1 or 2 millimeters below the surface — give off the same short, bushy sparks. These sparks indicate high carbon content. If the steel below the surface gives off longer sparks that flow out in straight lines, the file is case-hardened.

Hardness test: Besides the spark test, you can try to scratch the steel on the surface and the steel below the surface with a screw or drill bit. In both cases, it should be equally difficult to make a scratch mark. If the steel below the surface is softer, the file is case-hardened.

If you don’t have a grinder, you’ll first have to anneal the file (see Step 4), remove a bit of the surface, harden it (see Step 8) and then test for hardness. If the steel below the surfaces didn’t harden, the file is case-hardened.

Break test: Wrap the file into a cloth to prevent steel fragments from flying around your workshop. Secure the file into a vice so just a small portion sticks out. Then, hit that portion with a hammer to break it off. The material should break readily without bending and the core of the file should be smooth and light grey. If the material doesn’t break readily and the core of the file is coarse, the file is case-hardened.

Step 3: Designing

In this project, I’ll be making a bushcraft knife with a full-length, hidden tang. The tang is the portion of a knife that extends from the blade and connects the blade to the handle. Two common tang styles are the full tang and the full hidden tang. A full tang follows the contour of the handle and is therefore visible. A full hidden tang extends all the way through the handle, but is not visible.

The height of the thickest part of the handle depends on the size of your hand, but it is usually about 30 millimeters. If you want to make a full tang knife, I would advise you to use a flat file that is about 30 millimeters (or at least 28 millimeters) wide.

This knife-making project incorporates with a full hidden tang, because with this tang style the size of the handle doesn’t depend on the size of the file. You may either stick to my blade design and adapt it to the width and thickness of your file, or make your own design — just make sure the construction is the same.

Step 4: Annealing

Materials can only be worked with tools that are harder than the material itself. Files are hardened, so they need to be softened before they can be worked with a hacksaw or other files. The softening is done by a heat treatment called “annealing.” Annealing involves heating the high-carbon steel and cooling it down slowly. You’ll save a lot of work (and tools) if you do this correctly.

Annealing the file: Make a charcoal/coal fire and bury the file in it. Make sure there’s plenty of coal to surround the file completely. Blow air into the fire with a pump to speed up the heating process.

The file should be heated to the “austenitizing temperature.” At this temperature, the carbon steel is red-hot and non-magnetic.

After a couple of minutes of heating, expose the file to see if a magnet doesn’t stick to it. Also, see if the file is evenly red- hot. Do this in the dark, because you’ll see much more contrast between the different colors of the steel. If the file is still magnetic and it isn’t evenly red-hot, bury it in the fire and continue the heating process. If the file is non-magnetic and is evenly red-hot, you know that the fire is hot enough. 

Bury the file in the fire and heat it back up again (the file cooled down while it was exposed). Keep it at austenitizing temperature for about 3 to 5 minutes. Then allow it to cool down with the fire.

Step 5: Profiling

In this step you’ll cut out the bushcraft knife profile with a hacksaw and refine the shape with a file.

Marking out the knife pattern: Print and cut out my knife pattern or cut out your own design. Then, trace the pattern onto the annealed file (workpiece) with a scriber or permanent marker. I used a white pencil, which quickly faded due to the use of lubricating oil.

It’s hard to accurately mark out the knife pattern on the grooved surface of a file. I ended up using a caliper and a separate knife pattern, which I compared the workpiece to as I progressed.

Cutting out the rough shape: Secure the workpiece in a vice in such a way that you can make a vertical cut, and that the cut is as close to the vice as possible to reduce vibration.

For sawing material with a thickness of 8 millimeters or less, a blade with 32 teeth per inch is recommended. A minimum of 3 teeth should be engaged in the material at all times to prevent tooth breakage. Install the blade on the hacksaw frame with the teeth pointing away from you.
Keep the blade at sufficient tension to ensure straight cuts.

Don’t start a cut on a sharp edge or else less than 3 teeth will be engaged in the material. When sawing, apply a little bit of oil to the blade to reduce friction. Use long, steady strokes and only apply pressure on the forward, cutting stroke. Remove as much material per cut as possible. If the cut is wandering away from where you planned to cut, turn the frame gently in order to twist the blade into the right cutting direction. If you need to start a cut on an angle (with respect to the material), first make a shallow, perpendicular cut that will keep the saw in place when sawing on an angle.

Refining the shape: In this step, you’ll first use a cross-filing technique to remove the most material, and straighten the somewhat wavy edges made by the hacksaw. Then you’ll use a draw-filing technique to clean up the rough surface and flatten the slightly rounded edges produced by cross-filing.

Secure the workpiece in a vice in such a way that you can file in a horizontal plane most of the time.

Cross-filing (straight-filing): Use a large coarse (bastard, double cut) flat file. Finer files can also be used, but remove material less quickly. When filing, you can usually feel whether you’re using the right file and the right technique.

Grasp the handle in one hand and the tip of the file in the other, so that you can apply downward pressure. Place the file diagonally on the edge, so that the file covers a large area. This ensures that large errors (wavy edges) are corrected. Move the file from tip to handle, in a direction not quite parallel to the file, to prevent grooving. Use long, steady strokes and only apply pressure on the forward, cutting stroke.

Most people have a tendency to file slightly on an angle, as opposed to perfectly horizontal. Correct this error by changing the filing direction 90 degrees and flipping the workpiece 180 degrees in the vice.

Draw-filing: Cross-filing usually results in a straight edge but a slightly round cross-section due to the rocking motion of the file. Draw-filing is used to make the edge flat in the cross-section and perpendicular to the adjacent surfaces, and to give it a fine surface finish.

Use a fine (smooth, single cut) flat file. Grasp the file at each end. This way you can hold the file steady.
Place the file perpendicular on the edge. Push and draw the file from one end of the workpiece to the other. With this technique, be careful not to remove more material in the middle of the workpiece than on the edges. Also regularly remove filings, as these tend score the surface when they get caught up in the file.

Step 6: Making the Grind

The bevel, or grind, of a blade refers to the shape of the cross-section of the blade. Along with the steel type, heat treatment and the thickness of the blade, the grind shape and angle determine cutting performance and blade strength. In general, the steeper the grind and the less material behind the edge, the sharper the blade. On the contrary, the less steep the grind and the more material behind the edge, the stronger the blade. Furthermore, a less steep angle can also be combined with less material behind the edge. This gives a durable edge while it reduces friction when cutting. Examples are a convex grind, double grind and hollow- or flat grind with a less steep secondary grind.

Depending on the application of a bushcraft knife, sharpness is less or more important than strength. In this project, I make a 20-degree-angle sabre grind (giving a total- or “included” angle of 40 degrees). I think this grind provides a good balance between blade strength and cutting performance for a bushcraft knife.

To reduce friction you may want to convert the sabre grind into a convex grind.

Marking out the grind boundaries: Some knife makers use a jig that keeps the file on the same angle while filing in the grind, though you can easily file in the grind without the use of a jig.

To get a grind with the desired angle, you’ll need to mark out the grind boundaries. Measure the thickness of the blade with a caliper. If you used a file that tapers in thickness, measure the minimum and maximum thickness of the blade.

Calculate the grind width b:
b = T / (2tanα)
with blade thickness T and grind angle α.

Mark out the calculated grind width on the two sides of the blade using a scriber and caliper. Color the edge of the blade with a permanent marker so that a scribed line will stand out. Place the blade on a flat surface. Scribe the edge using a drill bit with diameter T (thickness of the blade). This way you get a line running along the center of the edge. If you used a file that tapers in thickness, put something underneath the tip of the blade to compensate for the taper.

Filing in the grind: Secure the workpiece into a vice. If you want to have a small ricasso (unsharpened section of the blade near the handle), clamp a piece of steel to the blade as a means of guiding the file.

File in the grind on both sides of the blade. Apply the same filing techniques you’ve used to refine the knife profile (Step 5). Regularly check if the edge is straight.

Step 7: Quenching and Tempering

Now the blade is ready to be hardened. The hardening is done by a heat treatment called “quenching.” Quenching involves heating the high-carbon steel and cooling it down quickly. After quenching, the steel is very brittle. The brittleness (and hardness) is reduced by a heat treatment called “tempering.” Tempering is a specialized type of annealing.

There are many ways of quenching and tempering knives and all yield different results. I use the most straightforward way in this project.

Quenching: Heat the blade evenly to austenitizing temperature. Keep it at austenitizing temperature for about 3 to 5 minutes. Don’t heat the entire tang. The end of the tang needs to stay soft, so it can be peened later.

Grip the end of the tang with a tongs. Wear work gloves to protect your hands from the heat. Quickly lower the blade tip first into a heat-resistant oil container. The blade should be at austenitizing temperature when it hits the oil. Use a sufficient volume of vegetable or mineral oil. I used about 2 liters of sunflower oil, but you might as well use 4 liters or more (for a more uniform quench).

Move the blade around in order to speed up the cooling process. Leave the blade in the oil until it has cooled down to about room temperature.

See if the blade hardened by scratching the blade and tang with a screw or drill bit. The screw should skim over the surface of the blade, barely leaving a scratch. It should be much easier to make a scratch mark on the end of the tang.

If the blade didn’t harden, either it wasn’t at austenitizing temperature when it was quenched or it didn’t cool fast enough (assuming the blade was made from a high-carbon steel file). If the blade didn’t cool fast enough, try to quench it in water or brine (water with 7 to 10 percent salt by weight): Water and brine result in faster cooling (water about 3 times and brine about 6 times faster than oil). Only try a water or brine quench if an oil quench didn’t work, because these quenchants are more likely to may cause cracking.

Tempering: The color of the steel gives an indication of the temperature to which the steel was heated.
Remove the scale on the bevel, spine and tang with sandpaper so that the color of the steel will be visible when tempering.

Heat the blade to 350 to 660 degrees Fahrenheit for about 1-1/2 hours in a kitchen oven. A higher tempering temperature yields a slightly softer material with a higher toughness, while a lower temperature yields a harder and slightly more brittle material. I would recommend tempering in two or more cycles of 1-1/2 hours, because of the inaccuracy of a kitchen oven.

For example, if you want to temper your blade at 480 degrees Fahrenheit (brown-red): First temper the blade at 350 degrees. If the steel didn’t reach a brown-red, temper again at a higher temperature.

Step 8: Making the Bolsters

For the bolsters I used the steel that I had left over from the old file.

Marking out the shape and the hole positions: Mark out two ovals measuring about 26-by-19 millimeters. The front bolster will need a rectangular hole so that it fits around the tang. The rear bolster will need a slightly smaller hole so that it fits around the narrowing at the end of the tang.

Mark out the rectangular hole in the center of one oval. Center-punch two holes inside the rectangle. Also, center-punch the center of the other oval.

Making the bolsters: If you are making the bolsters out of a coarse file, remove the grooves with a file to minimize the seam between the bolsters and the handle material.

Use a drill press or secure the workpiece into a vice. Use a drill bit with diameter T (thickness of the tang) or slightly smaller. Make sure to hold the drill perpendicular to the surface of the workpiece. Apply lubricating oil to reduce friction when drilling. Cut out the ovals with a hacksaw and refine the shape with a file. Make the holes rectangular with a small square- or flat file. You can also leave the hole in the rear bolster circular and make the end of the tang cylindrical.Both bolsters should fit snugly around the tang.

Make the hole in the rear bolster (very) slightly tapered. In the next step the bolsters and the handle material will be secured onto the tang by peening the end of the tang. The end of the tang will expand in cross-section and fill up the tapered hole, so that the rear bolster can’t slide off.

Step 9: Making the Handle

In this step you’ll make the wooden handle and assemble the bushcraft knife.

Assembling the front bolster: Slide the front bolster over the tang. If the bolster doesn’t quite fit over the tang, you might have to enlarge the hole, but for me rounding off the edges on the end of the tang also helped. If the bolster doesn’t readily slide down the tang, place a steel tube over the tang and hammer it to force the bolster into position.

Making the handle: Find a nice piece of hardwood. I used a piece of about 35-by-35-by-100 millimeters.

Mark out the rectangular hole. Use a drill bit with diameter T (thickness of the tang) or slightly smaller. Make sure to hold the drill parallel to the length of the workpiece. Drill two holes alongside one another. If the drill bit isn’t long enough, drill from both sides.

Remove the wood between the two holes by gently moving the drill perpendicular to the axis of rotation. I know this is not what a drill is made for, but it’s the quickest way of doing it.

Make the hole rectangular using a small chisel and/or file. The handle should now fit around the tang. Saw the wood roughly to the dimensions and shape of the handle.

Assembling the knife: Secure the blade into a vice. Use aluminum vice jaws or two pieces of wood to protect the blade against scratching during peening.

Apply some two-part epoxy adhesive to the tang, bolsters and hole of the wooden handle. Slide the handle and the rear bolster over the tang. Start hammering on the end of the tang. Be patient. The end of the tang should slowly “fill up” the tapered hole. Let the epoxy cure.

Finishing off: Refine the shape of the handle using a coarse half-round file and sandpaper. Remove the portion of the tang that is still sticking out with a file. Sharpen the knife with progressively finer grit sandpaper. Apply several coats of Danish oil to protect the wood from the elements.

Thanks for reading! I hope you enjoyed this project to make a bushcraft knife. If you have any questions or remarks, please don’t hesitate to comment on my original Instructables post, where you can find many more photos of how to make the knife.

I have entered this project into Instructables’ Great Outdoors Contest and the I Could Make That Contest.
If you like my bushcraft knife, please vote for it!