Forge a Knife




A quick knife with few tools and some prep work.

There are a lot of pictures, and I hope they help explain what I am doing. Sorry, no action shots. I don't have anyone to hold the camera : )

Let me know what could be clearer, and what I should take out. Doing it is so much easier than trying to explain how to do it for me.

Step 1: Where to Begin...

Since this is going to be a knife, we need some decent (if not good) steel. Hmmm, well, here's some bits of high carbon steel. All of these pieces started out as springs, some have been worked a bit.

If you start with a 'new' coil spring from a car, it will need to be cut down. I find it easiest to throw the coil spring into a bonfire, let it get hot, then cool off (anneal, or soften, or remove the temper) then cut it with an angle grinder
or high tension hacksaw (worth the extra few dollars).
If you skip the annealing, you use up a lot more blades and elbow grease whether you use the angle grinder or hacksaw. If you use a flat spring from a car, you don't have to anneal, but I find that kind of spring a bit awkward to hang on to.

NOTE: protect your eyes! The angle grinder throws off more sparks than a firework and they get into the most painful places.

NOTE: cut metal is HOT! An angle grinder is faster, but all those sparks are burning steel. Whatever you are cutting will get hot, even if using a slow hacksaw.

NOTE: cut metal is SHARP! Even a flat edge has burrs that will grab your skin and tear it open.

I did part of this last fall, so I don't have any pics of the annealing or cutting : P But here's the end result.

I'll be using the big round piece.

Step 2: Tools

Safety gear:
Something over your eyes
(gloves are a personal choice. Yes, they keep minor scrapes and burns to a minimum but they limit what you can do. I prefer to just be careful.)

(Prep tools:
Angle grinder or hacksaw to cut metal to size
Fire to anneal steel if needed)

Anvil (big piece of metal)
Tongs (or big pliers)
Fire tools
Quench tub (emergency burn first aid. Use something you are willing to put an open wound into : ) )
Hot cutter (edge of anvil will work, so would hacksaw or angle grinder)
Fuel for forge

Step 3: Play With Fire...

WARNING: Red-hot metal will cause third degree burns before you can react. Black iron can (and often is) hot enough to burn. BE CAREFUL!

Start a fire in your forge.

After the fire is going and there is a red/orange hot area put the steel in. If you are starting with a strait piece of steel (lucky you!) you can skip this part...

I need to straiten out the spring piece. Heat an area to orange, move it to the anvil, and pound on what sticks up. For me, putting most of the round on the bottom works best. Once the metal cools to red or less, put it back in the fire. Metal moves where it's hot, and easiest where it's hottest.

WARNING: if the metal gets to hot (yellow to white) it will start to spark. This is the carbon burning out and the iron burning away. If you catch it quickly, you might not have done to much damage, otherwise cut the burnt piece off and start over. It is no longer high carbon and can never be hardened, so it's useless for a knife blade.

Step 4: Pounding Out a Knife, Pointing the Tip

You can't finish one part of the knife at a time, you have to work the whole thing slowly. If you hammer out the blade thin, then try to do the tang (handle) part, the thin blade will be ruined by to much heat while the handle won't be ready to work yet.

I'm starting with the blade end. I'll thin the steel some and start a point on the tip.

Step 5: And a Little Bit on the Handle Area

Now that I can see where the blade will be, I'm going to outline where the handle will be.

The metal will bend in funny ways. The art of blacksmithing is to figure out what is going to happen and work with it.

Save your heat. Don't put a crooked piece of metal in the fire, use the last (red) heat to get ready for the next trip to the anvil. Plan what you want to do BEFORE you put the metal back in the fire, don't waste heat figuring it out later. Hot metal moves under the hammer a lot easier than cold, and that anvil will suck the heat out of your metal super fast.

Push the tip of the knife past the hot spot in the forge. I'm trying to heat just the handle area. work it flat, then reheat. Take it out and put the top edge of the handle on the edge of the anvil and hit it with the hammer half on and half off the anvil.

You will notice that the rusty surface has mostly disappeared : )

Step 6: Thin It Out

Starting to look like a knife.

Thinning it out is easier said than done. The metal wants to move in strange ways. Take a look at some of the plans of attack.

Step 7: Cut It Off...

Time to cut the extra metal off. You could let the metal cool, then use a hacksaw or angle grinder, but I'm going to hot cut it. Remember when I used the edge of the anvil to 'dent' the knife? Well, if you keep going, you can cut all the way threw that way.

I'm going to use a piece of flat, sharped spring held in the vice. Line up where the cut will be and hit it with a hammer-don't go all the way threw! That will screw up the hammer face. Go part way threw, rotate and go part way threw again. Then, grab the knife with the tongs and bend or twist until it breaks off.

Step 8: Handle or Tang

Oops, cut the handle a little short. Oh well, design modification time. Instead of a full tang this one will be a rat-tail tang. I'm not impressed enough with the overall shape to try an make a looped blacksmith's handle.

Drawing out the handle is done by heating it up, hitting it a few times on one side, then rotate it 90 degrees and hit it a few times, rotate back and repeat.

Step 9: Hardening the Blade

If you are going slowly or want to use a file instead of a grinder, let the knife cool slowly and do your shaping now.

Me, I'm trying for the quick way : ) I'll get all the forge time done first, and use the grinder instead of a file to shape the knife.

To harden the knife, you have to get the WHOLE blade ORANGE. Not red, orange. To do things right, you should test the orange heat with a magnet because when the metal is ready to be hardened (it has to do with which crystaline shape the iron is in and how the carbon is held in that latice) it becomes non-magnetic. If the magnet doesn't stick, you are ready to quench.

Again, no helper with the camera, so no pics of the actual quench : P

After the quench, test the edge of the blade by trying to file it. If the file works, the metal wasn't hot enough, try again (I had to). If the file skates across without biting into the metal, you did it!

A word about quenching. In this non-critical piece, I'm using water for a fast quench. Some steels need a slower quench like oil or they get TOO hard and can break VERY easily, as in the stress of fast cooling will shatter them in the water or if you drop them or even twist them to much.

You should, after hardening, temper the steel. This take a little of the hardness out but puts some flexibility back in. Two hours in the oven at 400-500 degrees F. should do it. Otherwise you could try to flame temper it-make the edge shiny and heat it from the back just enough so that you get a little bit of color (yellow, purple is probably to far). This knife didn't harden enough for me to worry about it (the file bit a little after hardening, but not much).

Looking at the blade, it's a little warped. I could reheat it, pound it flat and try another hardening but it's getting late, I'm hungry and the warp isn't to bad so I'll leave it.

Step 10: Grind or File to Shape

QUICK passes on the grinder, only a second or two to do the whole edge. To long in one spot and you will heat the metal up to much and ruin the temper-take to much of the hardness out and it will never keep an edge.

I started by grinding the bump off the back (coarse grit wheel) and evening out the cutting edge (fine grit wheel). If your grinder has a grinding wheel and a wire brush, then just do what you can. After the rough shaping, I sharpened the blade. Keep dipping the blade in a bucket of water, it will help keep the metal cool. when you can see that the water has evaporated, dip it again.

Step 11: Finishing Up, Or, What's Left to Do

I need to grind off the rest of the fire scale (the black stuff) and put a handle on it.

I should have thought more about the balance of the blade across the handle, hammer out the dip in the back and maybe a bit of a false edge. The rat-tail tang is easier to put a handle on, you drill a hole in the handle a little smaller than the tang, heat the tang up and burn the hole the right size. Any extra tang that sticks out can be handled in a number of ways-bent over like a nail, cut the extra off or put a nut on it to keep the handle tight. A loop handle could have been done, heating the middle of the tang, then bending the end up like a U until the tip touches the base of the blade.

Total time, little more than an hour, not counting the bonfire : ) Probably another hour to grind off the rest of the scale (or soak it in vinegar for a day or so) and make a handle.



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    197 Discussions


    3 years ago

    Good instructable! Some constructive criticism: first your going to have some trouble with that tang, not only because it is a lot lighter than the blade, creating balance problems, but also because its so thin, its likely to bend or even break in use; second if your steel does start to spark all is not lost, if the entire piece of steel is sparking, yeah scrap it, but is only a small part has sparked, get the metal red to orange hot and plunge it into charcoal powder and it fuses the carbon with the steel. Keep up the blacksmithing though.


    9 years ago on Step 2

    "all the tongs I make look funny"
    I'm with you, I can't seem to get any good ones yet, I use a large pair of channel locks and some tongs somone else gave me.

    2 replies

    Reply 8 years ago on Step 4

    Several problems-finding a vice powerful enough to do it cold or fast enough to do it before the heat is transferred to the vice. Either way, you end up letting a big tool do all the fun stuff, and you are just left with 'stock removal' (grinding off everything that doesn't look like your knife). Drop forging is what you are thinking of, stick a chunk of hot metal into a die that smashes it into shape. Of course the press starts at something like 100 grand plus another 20 thou for each different die...numbers are just guesses, but still several orders of magnitude more than I have for a hobby ; )


    7 years ago on Step 2

    iv made some knives from the bottom of my dressar drawer( mid quality steel) and folded them over a few times. but after i forged they seem to rust more then before they were intrduced to heat. anyone know why? o and nice forge. alot better than mine.


    8 years ago on Step 3

    arent you supposed to fold the steel like a hundred or so times for soemthing?

    4 replies

    Reply 8 years ago on Step 3

    That is an ancient Japanese technique for making Samurai swords. The metal was folded 12 times, giving it 144 layers that could be seen after polishing and sharpening.


    Reply 8 years ago on Step 3

    Except that the steel used wasn't homogeneous to start with, and so had 'personality' that worked it's way in (more-so than the Indian wootz, or damascus steel) . Plus, there were several methods of layering the steel-the soft center surrounded by layers of harder steel or a hard edge applied (welded) to a softer back...and no folding after that...

    2 layers folded becomes 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192 layers after folding 12 times. It's 12! (factorial) not 12x12 (squared).


    Reply 8 years ago on Step 3

    Why? I'm starting with good steel, not the crap that comes out of a primitive smelter.

    The early iron-smiths had to average out the carbon content of what they had, and so had to mix the metal by folding it. Bessimer fixed that.


    Reply 9 years ago on Step 2

    Pavers are made from cement.  Brick are made from fired clay.  You can tell the difference by looking at the surface (sometimes you have to look closely), cement has a sandy and gravel texture, clay may have grog (pre-fired clay) in it but the texture is much smoother.


    8 years ago on Step 11

    grandissimo !!! ... you are great ;-)

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    8 years ago on Step 2

    what are you using for fuel? Just plain wood, or is that (Char)coal underneath?

    1 reply
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    Reply 8 years ago on Step 2

    All three : ) I have a limited supply of (mineral) coal that I'll use when I don't want to keep feeding the fire, but mostly charcoal from old campfires (scout campfire pits where the fires aren't allowed to burn out are good sources) and wood.

    I was reading your article on the war sword and how it was made with old leaf spring metal, to create swords/knives/daggers, and found it very interesting. I work for and being
    that we work with these, things all day. Its nice to see them put use rather just sit there at a scrap yard or in the wear house, and with customers always buying new leaf springs --- obviously they have
    old leaf springs; so we decided to write about a trend we've spotted on your site and show our customers what some are doing with their old leaf spring metal. So we wrote an article about it which you
    can find here. Hope you enjoy!