BLUE STEEL by Joe Garnett
HOW A KNIFE IS BORN
In my last article I rambled on about different kinds of blade steels and I finished by talking about the benefits of buying your next knife from a custom craftsman as opposed to a factory-made knife. This time I am back to share with you exactly how someone like myself would do this. In a past issue of the journal, Tim Chilcott of Greenman knives walked us through the process of making a full tang stock removal knife so I shall be taking you through the process of how I forge a hidden tang blade. Let’s get started!
- Draw a design.
- Time to get creative! It is much easier to forge to a desired shape as opposed to trying to think of a shape whilst forging, so drawing a design is important. At this point you need to think of what you will use the knife for, and design it accordingly. It must also fit the person to be using it and remember that you will be making it so don’t design too crazy a shape. Draw it in full, including bevels and handle shape, so you can check the proportions. I often draw designs in two different planes using square layout lines as guides. In this case I am going to make a hidden tang Puukko style blade.
- Defining shoulders.
- Let’s start forging! It is easiest to work off a bar of steel to start with than juggling a small piece in tongs. The first step is to define the shoulders for the tang. This can be done either with a guillotine tool, using a set hammer and someone with a sledge hammer (a striker) over the edge of the anvil or just with your hammer and the anvil edge. It is good to get the shoulders as sharp and level as possible. They will be evened up later but the better they are now, the less grinding we must do.
- Forging the tang.
- The tang should be tapered from shoulders to tip when viewed from both the top and the side. I work along the tang from shoulders to tip, alternating between reducing the width (which also makes it thicker) then turning it on its side to forge the thickness back to true. You can use the peen side of your hammer (depending on the hammer pattern), The horn of the anvil or the side of the anvil to make indentations, forging the length out faster. You don’t need very much material to start with; an inch or so will comfortably forge out to roughly a 3.5” tang. Finish by straightening the tang and aligning it with the bar.
- Cutting off.
- Now we cut the knife from the bar and hold the tang we have just forged with a pair of tongs. The bar can be cut on the anvil using a hardy tool or hot set, using and angle grinder or using a hacksaw. Make the cut at an angle, about 45° or so. The final length of the blade will be a little longer than where it’s cut so it’s time to refer to your drawing again. Remember that it is easier to remove material than add it!
- Forging the blade
- Now we do the opposite of what may seem logical and forge the tip of the blade over. This creates a nice curve up toward the tip of the blade and avoids any cracking that might occur from a rough cut. Here the rest of the blade profile must be forged. Also, there should be a slight taper from shoulders to tip of the blade, this is called a distal taper and makes the tip of the blade much finer. As I will be putting a Scandinavian grind on this knife, I will not be forging bevels. Don’t forget to add your touch mark/initials/logo at this point!
- Straighten and align.
- Now is the time to get everything straight and true. This can often be easier at slightly lower temperatures where the metal is less plastic but still hot enough not to work harden (a dull orange colour). Ensure the spine and the blade are the same thickness and that the tang and the blade both taper from the shoulders to their tips. I straighten first the tang, then the blade, then align the two.
- Grind profile.
- At this point we have a piece of metal that looks vaguely like a knife blade, but now the profile must be cut out to get the shape perfect. This can be hard to do by eye, so it is a good idea to cut out and draw round or simply stick on the design that was drawn at the start. (Insert Picture 17) It is important to remember to square up the shoulders at this point because it is most easily done accurately with a file and so cannot be done once the blade is hard. Using scribed lines or a hardened steel filing jig are the most accurate methods of doing this.
- Grind Bevels.
- At the design stage the bevel type should have been decided and the time has come to grind them in. Scribe or draw layout lines onto the steel and grind your bevels to 90% ensuring your leave a little metal to be removed post heat treat. Leaving extra material on the edge means that there is a reduced chance of warping when hardening.
- Drill Hole
- The design of the knife may include a pin for helping with holding the blade in the handle. It is important at this point not to get carried away and to drill a hole for a pin to go through during the handle construction. The hole should be 0.5-1mm larger than the pin that will be used.
- Stress relieve the blade.
- Now we get onto the heat treatment of a blade. There are several steps to this and it would be easy to skip one, but each is vital for a good blade. The best heat treating is done in a carefully controlled electric furnace but here I describe the old-fashioned way. First, we have stress relieving which is vital in avoiding warping or cracking when hardening the blade. Due to forging the steel, tension has been put into it and this must be relaxed. Heat the blade to between 500°C-600°C, then let it cool as slowly as possible. Leaving in the embers of the fire to cool with the fire is a good way to do this. The temperature can be determined by looking at the colour in a dark place.
- Grain refinement.
- This is also known as normalising. As steel heats up, the grain size decreases up until critical temperature, beyond which it starts to grow again. A small grain size is necessary as a large grain would produce an almost saw-like edge that would be very brittle. (Insert Picture 22)The critical temperature will depend on the type of steel and can be judged by colour and by using a magnet; critical temperature is slightly hotter than when the steel becomes non-magnetic. Heat the blade to critical temperature (just hotter than when it stops being magnetic) and let it air cool to room temperature.
- This is where you lump of metal becomes a knife. Slowly heat the blade, moving it back and forth in the forge to get an even colour across the blade. The tang does not need to be hardened and often it is better if it is not. Heat to critical temperature. Once the correct temperature has been reached, quench the blade in oil, moving the blade up and down or backwards and forwards as if cutting the oil, never sideways as this encourages warps. It doesn’t need to be in the oil too long, just 10 seconds or so, then pull it out and let it cool to room temperature. Once cooled, use a file and run it across the surface, it should skate across as if on glass, and shouldn’t cut the metal at all. The blade is hard!
- At this point the blade is like glass; very hard but very brittle. It must now be tempered to toughen it. How much it is tempered depends on the job it is being used for as I explained in my last article. This can be done with a large block of hot steel or in a kitchen oven. The specification sheet for the steel type will give instructions for tempering. As a general guide, putting the blade in the oven at 200° for two separate sessions of an hour each is a good method. Just leave it in the oven and when the time is up just pull it out and leave it to air cool. If using a hot block, first the edge must be ground a little so it shines silver. The blade is then placed on the block edge up, with the point protruding a little. The aim is for an even straw colour along the shiny edge. As soon as this is achieved, the blade is quenched in water to stop further heating of the edge.
- Final Grind
- It is time to finish grinding the bevels of the blade, either on a sharpening stone or with a grinder, the final edge is put on the knife. If using power tools, regularly dip the blade in water to cool it. It is important not to over heat the blade at this point and ruin the temper.
So, there we have it - from a bar of steel to a beautiful knife blade. I hope this has been of interest to you and I shall be back soon to make the handle. Goodbye until the next time !