This is the process I used to build my kickass fire sword, which has an average burn time of 3 or 4 minutes (depending on how fast I spin it).
Fire spinning is dangerous, seriously. Here are some basic guidelines if you're thinking of picking it up. If you burn yourself or cause any other damage, or get in trouble with the authorities for burning somewhere you're not supposed to, I accept no responsibility for it.
1) Always ALWAYS have an experienced safety person standing by with a bucket of water/fire extinguisher and a wet towel/fire blanket.
2) Wear natural fiber clothing when you burn, as artificial fibers can melt and fuse to your skin.
3) Spend many, many hours playing with the prop before you light it on fire, get used to the way it feels and how it moves.
4) Consult with seasoned fire spinners before you attempt anything. There are lots of communities online if you don't have one in your town, and I can also answer general questions in the comments.
5) This sword puts out a lot of heat, any tricks that involve thrusting or holding the point below the level of the handle will burn the crap out of your hands if you do them before the sword has burned down a bit. If it hurts, drop the sword.
6) Don't burn inside, or near anything flammable (trees, furniture, dry grass, etc)
7) Don't burn while intoxicated.
8) For fuel, I use white gas (the naptha kind, NOT GASOLINE). With the tip of your sword resting in a container, carefully pour fuel over the wick until the whole thing is wet. Spin off before you burn to get rid of excess fuel, I do this by raising the wet sword above my head and chopping down, stopping it sharply at the bottom. This flings the fuel at the ground instead of onto you.
9) Check your local regulations to see if fire spinning is even a thing that you can do. If it is, be familiar with the regulations on where you can burn, required safety equipment, and how far you must be from your audience.
10) You are going to burn yourself, even if you're careful. I recommend wearing leather gloves when spinning sword to give your hands a little extra protection.
Intro Photo by Lara Evensen
Step 1: You Will Need:
Kevlar Tape Wick - 30 or 40 feet of it (My sword has four layers, and each layer uses about 10 feet of wick). The wider and thicker the better. The thicker the wick, the fewer layers you will need to do. Trick Concepts sells it, as do a few other places. Google "kevlar wick" and you will get many, many results.
Aluminum Tape - Most hardware stores carry this. The aluminum creates a heat shield between your sword and the fire. This will make it last longer.
Bolts, nuts, washers - Two of each. The bolts should be as long as your sword is thick, with an inch or so extra to account for the wick.
Wooden Practice Sword - The one on the far left in this picture is pretty much the one I used. It needs to be decently sturdy, you will be drilling holes in it and you don't want it to split when you do.
Large Eye Bolt - For making the pommel
Steel Wire - To make the pommel nice and counterweighty
Grippy Tape - Like the stuff that is used for hockey sticks
Drill - For making bolt holes in the sword
Awl or Large Needle - For guiding the bolts through the kevlar
Pliars & Screwdriver - For setting the bolts
Heavy Duty Metal File - For removing excess bolt
Scissors/shears for Kevlar - Anything you use to cut kevlar will become dull very quickly, so don't use scissors you care about. Kevlar shears are a thing that exists, though emergency scissors like these are probably cheaper and should work fine.
Step 2: Drill and Wrap
Drill two holes in the blade of your sword, one about six inches up from the top of the handle and one an inch or two down from the tip. You seriously need the buffer between the handle and the wick if you want to be able to hold your sword for more than a second. Even a few inches from the flames, this sword gets very hot. If you want to add a pommel (which I recommend), also drill a hole into the end of the handle big enough for the eye bolt. After the holes are drilled, wrap the entire blade in aluminum tape, including the point.
(Note: this picture was taken when I was replacing the wick on a sword I'd been using for a few months, which is why it's a little sooty.)
Step 3: The Wick
Start wrapping your wick around the blade in a spiral, starting at the bottom and wrapping as tightly as you can. I wrap a hairband around the end to hold it in place. Wrapping around the point is tricky if you want to preserve the pointed shape. I tie a sort of knot around the end and then fold the wick at a right angle to start wrapping back down towards the handle. Stick a needle or awl through the wick to locate the bolt hole and hold the wick in place as you go. You want three or four layers of wick for a sword that lasts three minutes or more. The thicker your wick, the more fuel it can hold and the longer it will burn. Swords are deceptively short-lived because of their surface-area-to-volume ratio.
Step 4: Bolt in Place
Now for the really, really annoying part. Using the needle or awl as a guide, wiggle the bolt though the layers of kevlar and the holes you drilled. I know of no easy way to do this, as kevlar is tough and cutting holes in the kevlar will make it fray faster. Pliers are helpful at this stage, turning the bolt with the screwdriver helps too. Once you get the bolt through, stick a washer on the end and tighten the nut. Remove excess bolt with the file, you do NOT want the hot end of a bolt sticking out where it can gouge you.
Step 5: Handle and Pommel
Screw your eyebolt into the end of the handle and start wrapping it in the wire. With all this wire I managed to get the balance point to right around the base of the wick (this is when the sword is dry though, the fuel adds quite a bit of weight to the blade).
If you want a grippier handle, wrap it in your grippy tape.
Step 6: Burn, Baby, Burn!
LéoD33 made it!