Tuesday, June 8, 2010
How to Build a Knife
First thing's first...design the blade!
The design of your knife is the single most important element of its construction. In my designs I try to find the best compromise between functionality and looks. I abhor inefficient fantasy designs and have a profound dislike of Persian-style blades--you know, the kind shaped like a banana--but if you like a specific design, go for it.
First, plot out the blade and handle shape on graph paper. Try to get it as close to actual-size as you can. The less changing you have to do to the design once it's on the steel, the better.
Now you need to decide how to attach the handle to the blade. There are three common methods of doing this: a full tang, a partial tang, or a through-tang. A full tang has the same profile as the handle of the knife, and the meat of the handle is formed by two slabs of wood (scales) to either side of the tang; most good knives are made this way. The knife I'm making here is a full tang knife. A partial tang is the most inconspicuous of the three and, in my view, the hardest to make. In this design the tang is a rod that protrudes back from the blade and is completely hidden inside the handle, secured with a rivet or two. Japanese swords and sushi knives are made this way, though the latter is secured with a cuff rather than rivets. A through-tang knife is similar to the partial tang except that the tang extends all the way through the handle to be secured by a nut or by peening on the other end. Ka-bars and most turned-handled knives are made this way. Choose whatever best suits your project. There is plenty of info on the web if you're not going to make a full-tang knife, though I recommend it for a first project.
Ingredients: choosing and finding materials for your knife
Next: choosing and obtaining materials. You'll want a carbon steel (NOT stainless), such as 01, which I used for this knife. There are other steels out there, but 01 is good to start with. You don't want stainess steel because it has to be sub-zero tempered, which is bad. It also doesn't make as fine a blade. You'll want a slab or bar about 1/8 to 1/4 of an inch. I believe my steel was 3/16. You'll also need handle material, such as wood, micarta, bone, leather, cord, stone, gem, another type of metal, mammoth ivory, or meteorite. Believe me, they've all been done. For my project I decided to use Purpleheart wood. It's my favorite type because it's unique, beautiful, tough, and above all, cheap. You'll also need pins or rivets and epoxy to attach the handle. I used a brass rod for my pins.
The first picture is me with my chosen slab of steel. Notice the missing sock--this is vital to the success of the project ;-). I got it from a Northern Tool Supply, an industrial metal and tool supply warehouse a few miles from me. Finding steel was one of the most difficult parts of this project for me, because I live in a pretty rural (Maine is pretty much all rural) area and there's not a whole lot around. You can salvage steel from saw blades and the leaf springs from cars of you can't find a commercial dealer, but chances are you can.
The second picture is of the Purpleheart wood, which I got at Atlantic Hardwoods, a flooring and marine hardwood supplier in Portland. Again, there's probably something near you, just try the yellow pages or the internet.
After you have the steel, trace your design onto it in permanent marker. You'll notice that my tracing is a little bit bigger than my design--I had to elongate the handle to fit my hand, and the blade just didn't look good unless it was a good inch longer than the grip. Now you're ready for the next step.
Rough cutting the blade--the easy part
Now it's time for the really fun part. Here's what you're going to need:
A hacksaw or jeweler's saw and several blades
An angle grinder with a hard wheel and flap wheel
Files (if necessary)
Necessary protection (glasses, gloves, jacket if you don't like sparks)
And a steady hand
Step one: cut out your blade using a hacksaw or jeweler's saw. If you're using a thick piece of steel, go with the stiffer hacksaw. I recommend standard, medium-to-fine blades. If you're using a relatively thin piece of metal and you have a jeweler's saw, you can cut out a pretty close profile which will save you some grinding in the next step. I just cut out a rectangle around my basic shape--using a hard, steel-cutting wheel, you should be able to grind through the excess pretty quickly. See picture one, below.
Step two: slap that blank in a vise and start grinding. Use the hard wheel on your angle grinder to cut away excess metal from the profile of the blade. This should be pretty self-explanatory; you're just cutting out a shape. The different colors that appear along the edge are just products of low-level heat changes in the steel, and won't compromise its strength or finished look. Remember those colors, though, you'll be using them to your advantage later when you heat-treat the knife. See picture two below for an action shot, and three for the completely cut-out blade.
Step three: grinding the edge. Use the flap wheel (the one with flaps of coarse sandpaper) to gently and EVENLY grind a slope to the middle of the steel. Don't go past the center, because that will give your edge a dip--and you don't want that. Picture four is of the job at this step, half done. Grind the other edge the same way, until the edge becomes an edge. If you think you're starting to go too far, STOP! Be patient. This is possibly the most delicate step in rough-shaping the blade. Work the edge evenly, so that it's straight and consistent. See below, picture five, for the finished shape.
Step four: drill rivet holes. Make sure you use a drill bit the same diameter as the rod or rivet you plan to use. They can go anywhere and be any number, so get creative. Sorry, I don't have a picture of this...if you can't figure it out, try making something simpler, like a birdhouse.
Rough cutting the blade--the easy part
Finishing the blade (first time, no joke)
Before heat-treating the blade you'll need to finish it. Of course it's fitting that after the most fun part of the process, you need to endure the least fun part. Nevertheless, it's important. Why? To ensure you put out a quality product, of course. I also decided to add some simple filework to my blade during this step. To finish the blade, you'll need:
Sandpaper, grits ranging from 60 to 220. I use a sanding wheel and power drill to save time.
A sanding block, even if you're also using a sanding wheel.
Time. Lots and lots of time.
This step is fairly self-explanatory. The first picture below is early in the process, sanding with a rigid sanding wheel. These things aren't necessary, but I do recommend them for rough finishing. I saw 'em at the hardware store and thought I'd give them a spin. Ha-ha, I made a pun.
Work through through the successively finer grits until you reach about 220 grit. There's definitely a technique here--first of all, don't skimp. You'll regret scratches you don't take the time to remove during this step. Always work each successive grit perpendicular to the direction you worked the one before; so if you sand the blade lengthwise with one grit, sand across the blade for the next grit. Also, be sure to cover all the visible surfaces of the blade. Give special attention to the ricasso (the area where the blade meets the handle) and the spine/handle edges of the knife. It's better to sand part of the blade that will be covered than to leave a visible part of it unfinished. I'm sorry I don't have more pictures of this bit, but it's boring and I guess I forgot to take them.
Now, for that filework. You can see the process in the last three pictures below. First, choose your design and mark out even spaces on the part of the blade to be worked. Second, draw the pattern on the knife, using the marks as guides. I chose a pretty simple zig-zag pattern, but you can see a couple other possibilities on picture three. There are literally infinite possibilities for filework, but I'd try a very simple one on a first project. Bad filework can ruin an otherwise good knife. In the last picture you can see how I filed out the pattern. Use needle files. It's pretty simple; just be careful not to scratch the side of the blade. I did in one or two places, but later sanded the scratches out.
Once you've finished sanding and you've done any other ornamentation, you're ready for the next step: heat treating.
Heat Treating--for the little pyro in all of us
Here's probably the most technical part of the entire project--heat-treating the blade. You can use either a coal forge (as I did), a gas forge, or a torch. The last should only be used on small knives--maintaining high heat on a big blade would be hard with just a torch. See picture one below to see me starting the fire.
Heat-treating consists of two steps, hardening and tempering. In hardening, you heat the blade to a critical temperature and then quench it. This changes the structure of the steel so it's extremely hard but also pretty brittle. A knife in this stage, if dropped, can crack or shatter like glass. The next step, tempering, is done by heating the knife to a lower temperature, around four hundred degrees. This makes the knife less brittle, while still keeping a relative amount of strength.
Now, You'll need a hardening bath. For 01 steel, you should use oil. Different types of steel require different methods of quenching--oil quench, water quench, air quench, etc... again, I recommend 01 steel because it's easy to heat treat and doesn't require anything more complicated than a bucket of motor oil. See picture two. You should be able to immerse the blade completely. The second thing you'll need for hardening is a magnet. This will help you determine the hardening temperature, because at that point the steel becomes non-magnetic. See picture three--I keep the magnet on the hood of my forge, specifically for this purpose.
Now to start. Make a fire on your coal or gas forge or light up your torch--heat the blade by the spine, so as not to burn off the edge. Steel will burn off or melt into an unusable foam-like metal mousse if it's heated too high.
So, you're going to heat the metal to a medium-high orange heat, until the steel becomes non-magnetic. Just tap it against the magnet while it's glowing, and if it doesn't stick, it's ready. At this point you'll want to let the steel cool slowly in the open air, a couple times. This is called annealing, and relieves stresses in the steel cause by the rolling and milling process. After you've annealed (three times is a good round number), heat it to the same temperature you have been, but instead of annealing it, plunge it into the oil bath. Wear gloves because there's going to be some fire here. See picture eight. When you take the knife out it'll be smoking and the entire room should smell like the French fry tent at the county fair. To test the edge, run a sharp file over it. If it's hard, the file should skitter over the edge without making a mark, as in picture ten. You've hardened the blade at this point, so be careful. It'll break if you drop it.
Now, there's not much you can do with the blade until you temper it. Put out your fire, go inside, and preheat the oven. Your steel might have come with tempering information on it. If it did, chose your hardness from the sheet and use that temperature. You'll want a medium hardness for a knife. The eleventh picture of this step is an illustration of the tempering colors--these are a visual aids for measuring the temper of the blade. The higher the temperature, the softer and springier the blade will be. Try to shoot for a brown or purplish color, which will usually show up at about 400-450 degrees. If you don't know exactly what temperature to use, go for 425 degrees fahrenheit. Put the blade on the middle rack and let it cook for one hour. When the hour's up, the knife is ready. Congratulations. You've officially made a blade--though to turn the blade into a fine piece of cutlery, you'll need to do a little more work.
Finishing the second time: son of a...
So you've finished heat-treating the blade, and you may have noticed some inconsistencies on the blade--namely, tarnishing, and if you're lucky, scale! Scale is that flaky stuff that formed on the blade when you quenched it during hardening. Lucky for us, though, it isn't flaky enough to just flake off. You'll need to repeat the same finishing process you did earlier, though this time you'll be going to a somewhat higher grit. You already know how to finish the blade, so get to work. Take your time, and be sure to get the scale this time--that stuff is pretty tricky. Go past 220 grit and continue until you reach about 350 or 400. At this point, you're ready to polish the blade. The polishing isn't strictly necessary, but I did it because I could and it also looks really nice. You'll need a bench grinder, a heavy polishing wheel and at least the black polishing compound (emery stick).
Attach the wheel to the grinder. If you're lucky you'll have an actual polishing grinder--the kind with a tapered screw to hold the wheel. If you're like me you'll have to take your normal grinder and make a spacer out of duct tape to keep the wheel tight. Either way, the polishing is about as self-explanatory as the finishing. One thing to remember is NEVER to contact the wheel with the edge of the knife in a way that will make the edge catch. This is bad and I'm not responsible for injuries incurred should you be this careless. When you have to polish the spine side of the blade, hold the cutting edge angled well away from the wheel. Be sure to get the spine and handle edges of the blade as well. When you're happy with the finish, you can proceed to the final step--making the handle.
Getting a grip
Here's the last leg of the race, the run from third to home. Hopefully by now you've chosen your handle material--I'll be using wood and securing it with brass rivets and epoxy.
First, cut your handle slabs. Of course, if you're making a partial tang or through-tang knife this part will be a little different. With a through-tang, you'll most likely be drilling a hole through the handle lengthwise. With a partial-tang you'll also be cutting slabs, but you'll be cutting a channel in each one and gluing them back together. Find info elsewhere on the web if you're doing this--it's out there. My project is full tang, so it'll have two slabs on either side of the tang. Use a table saw or a chop saw if you have one. A hand saw will also do, but you'll have to plane the side of the wood that contacts the tang if it's rough-cut.
First, file down and sand the end of the wood in the ricasso area. Once it's glued you won't be able to shape it any further. Do this by placing both pieces of wood back-to back in a vise and filing them at the same time, as in picture four. This will ensure that both pieces are even. The rest of the handle doesn't have to be cut to shape--in fact, it shouldn't be as this leaves more room for error.
When you're ready, mix your epoxy and spread it on the back of one of the slabs. Lay one of the slabs onto the handle, as close to where you want the handle to be as you can get (picture five). Try not to get too much epoxy on the blade--it can be removed, but if there's a lot of it you'll be in trouble. Put the blade and slab in a padded vise until the epoxy has set enough to be rubbery and not wet--now, carefully, drill through the holes in the blade and though the wood using the same diameter bit you used to drill the handle. Repeat the process with the other slab--attaching it to the remaining side of the handle, putting it in the vise (picture six), and then drilling back through the holes you just drilled to complete the rivet holes. Wiggle the drill in each hole to leave just enough space to peen the rivet.
Scrape any epoxy off the blade with a Brillo pad and, for stuff close to the handle, a razor blade. Be careful with the razor, though, because it can scratch the blade and do other considerably more invasive things to you. Now, put the handle back in the vise and let it dry overnight. At this point you should tape the entire surface of the blade, to prevent scratches
When the epoxy is dry use a jig saw and/or a SurForm file to cut the wood down to the handle. Use a finer file to refine the handle until it's in its final shape. At this point, put your rivet rods in the holes, cut them so that they're about an eighth of an inch above the wood, and peen the ends down with a small ball-peen hammer. See picture eight for how this should look. Once all the rivets are peened, file them down and sand the grip up to about 150 grit. By now it should look like a knife. Just a couple more steps and it'll be done.
Using the tripoli brown compound and a NEW polishing wheel (I.E. you'll have one wheel devoted entirely to the brown compound), buff the wood grip. This should be easy--just a couple passes over the wheel and the wood will be brought up to a nice semi-luster. Take the tape off the blade, and you're ready for the FINAL step, sharpening.
Getting your edge on
Now, what use is a knife without a sharp edge? Answer: nothing, really. So get out your stone and your steel and get to work. There's a wealth of info on sharpening out there, but here's a primer that will get you there with a minimum of reading.
You should have a good sharpening stone--big, and ideally double-sided. You'll also need some sharpening oil (mineral oil works fine), and a sharpening steel if you like. You'll find the last one in most any kitchen.
Spread a thin layer of oil on the rough side of the stone. Now, hold the blade at a 45-degree angle from straight along the length of the stone and a 20-degree angle from the surface, using your thumb to prop the blade up. That might be a little hard to understand, so look at picture two for an illustration. Picture three just shows the proper edge angle, about 20 degrees as noted previously. Move the blade across the stone in a cutting direction. Sharpen the tip by raising the handle up and rotating it so every part of the tip has contacted the stone. See picture four for a visual aid. Trust me; once you do it it'll be easy to figure out. Flip the blade over every few strokes to get the other side of the edge. Test the edge with your thumb. Once you can feel a clear, sharp edge on every part of the blade, repeat the process on the finer side of the stone.
Now, use the kitchen steel to put the final, fine edge on the knife. There's not much special skill here, just keep that 20-degree angle you used on the stone. You probably know how to use a sharpening steel already if you've ever cooked, but if you haven't it's simple. move the knife in a cutting direction as you did with the stone, making sure every part of the edge contacts the steel. Alternate between each side of the blade on each stroke. Give it about ten to twelve strokes, and it's done. Keep in mind that the steel does not sharpen the blade by removing metal--instead, it reshapes a microscopic flake of steel on the edge of the knife known as the thinning metal burr. You'll have to steel-sharpen the knife often and occasionally stone sharpen it to maintain the edge.
To test the edge, hold a piece of copy paper in one hand and, cutting near where you're holding it, try to slice the paper into strips. If it tears or won't cut, sharpen the blade again using the fine side of the stone. If the blade is sharp, though, you'll be able to slice the paper into ribbons.
Finished! And some of the mistakes I made along the way.
Well, there you go. A finished knife. I'm happy with the way it came out--yet I'm not immune from mistakes. Picture two shows my most egregious error--when I drilled the holes through the first handle slab I hadn't let the epoxy set fully, and the slab slipped before I drilled without me noticing it. It was only after I drilled three of the holes that I realized that the wood wasn't covering part of the handle. Fortunately I one of those holes was in the right place, and I was able to gently move the wood back into the right position before it dried. I continued along with the project and disguised the holes with two plugs of Purpleheart wood. Since I took the picture the wood has darkened and the plugs have become a little more blended with the handle. I kind of like them--they add a little character to the blade.
The third picture is hard to see, but it shows a hairline fracture on the spine of the knife. At first I thought it was just a tough scratch from when I did the filework, but I realized later that it was on both sides of the blade. It's small and I don't think it really compromises the blade's strength, as it only extends about three eighths of an inch in.
I guess this section is just here to let you know that we all make mistakes, and you shouldn't punish yourself for making them. Building a fine knife is something to be very proud of, and a few mistakes make it no less amazing.
Edit: due to popular demand and my own copious amounts of free time, my sheathmaking instructable is now up. Check it out: http://www.instructables.com/id/How-to-Build-a-Sheath/