This instructable will take you through he steps necessary to constructing a waste oil forge and lighting it. The forge takes in oil, atomizes it, and injects it into a combustion chamber along with a steady stream of air (provided by an electric leaf blower in my case). The oil will vaporize in the combustion chamber and ignite generating enough heat to melt aluminum, brass, iron, and potentially hot enough to fuse low-temp ceramics. The beauty of this machine is it’s almost as cheap to build as it is to run. I was able to construct mine out of some scrap metal and about 30 dollars worth of hardware supplies, no welding required! Additionally this forge should be able to accept a wide range of fuels, I primarily ran mine off of used fryer oil I collected from the bins behind restaurants, but I’ve found that this thing will readily burn; used motor oil, hydraulic oil, melted candle wax, even warm bacon grease. While some fuels work a little better than others, as long as it’s a liquid hydrocarbon this forge will eat it and give you tons of heat.

WARNING: This beast is dangerous! Your dealing with hot oil and temperatures exceeding 2700 degrees Fahrenheit, so, do it outdoors away from structures and anything flammable. Never leave this thing running unattended even for a minute, don’t even turn your back on it. Keep in mind, WATER MAKES OIL FIRES WORSE! Way worse, so have a fire extinguisher ready. Wear dense clothing you can take off quickly. And lastly, keep your distance when your not working with it, of course you’ll have to mess with it some while its running, but limit your time around it and you’ll limit your chances of getting a burn.

Step 1: Necessary Parts

First off I don’t expect you to be able to find the exact same parts as I did to create this forge, as long as you have the same essential parts and you have modeled the right shape for the combustion chamber it’ll work, there are a dozen different ways to build this. Ill tell you what I used to give you an idea:

-A Steel container: for the body of the forge, I used a scrap L-joint from a metal fireplace duct. The inside must have a diameter of about 1 foot doesnt even need to be cylindrical as long as it houses the combustion chamber with plenty of room for insulation

-A Blower: I used an cheesy electric leaf blower bought from ebay for like 3$ no good for yard work but perfect for this project

-Threaded metal pipe 1-1.5 in dia (it must fit the blower’s exit-tube diameter) must be at least 2 feet long.

-Another threaded pipe same diameter between 3 and 5 in long

-A two-ended threaded female connector to fit the pipes

-Materials for paper mache (newspaper, glue, cardboard, etc.)

-An Atomizer: something to create a constant spray and will accept oil, I used a generic garden sprayer, an airbrush tip gravity fed from a raised tank would work fine.

-Heat gun

-Refractory: at least 2-4 square ft. depending on the size and shape of your forge. this is the heat proof material that is poured and sets like concrete, there are several options for getting refractory, the easiest and more expensive option is to simply buy a refractory mix, either from a fireplace supply store or an online supply. It needs to be rated to withstand temperatures of at least 3100 degrees Fahrenheit. You can also make your own refractory, there are several DIY pages that can walk you through this step.

-Funnel and cheese cloth: you use this to filter the waste oil before it goes into the sprayer (fryer oil tends to have "chunks") the debris will quickly clot spray nozzle otherwise

Step 2: Modeling Combustion Chamber

The first step in construction is creating the shape of the combustion chamber out of paper mache. This form will then be suspended inside the metal body and liquid refractory will be poured around it. after your first ignition this paper mache form will burn up leaving a cavity in the refractory the same shape. The important thing here is that the paper mache form fits the form of the body you picked to use. The paper mache form must fit inside the body so that there is at least an inch of space between the inside walls of the body and the outside of the form. The paper mache entrance tube should fit snugly inside the metal pipe. the exit nozzle tube should be around an inch in diameter

While building the form keep these things in mind-

- It cannot be straight, whatever body you choose the entrance hole must have at least a 45 degree angle in relation to the exit nozzle. In other words if you were to look through one side of the forge you should not be able to see out the other. The bend in the combustion chamber allows any unspent fuel to slow down and burn before it gets to the nozzle. Otherwise a straight chamber would result in all the burning material to be ejected out the nozzle at once and no combustion cycle would take place.

- The papermache form will have to withstand quite a bit of weight from all sides as you pour the liquid refractory around it. It also must be leak proof so the more layers of paper mache you add the better, you need to be able to throw it around with out it falling apart or breaking.

- Once you’ve got a strong paper mache form, you’ll need to water proof it so it doesn’t disintegrate before the refractory hardens, I used spray silicone on every inch of it but latex paint should work the same. It’ll all be burnt out of the forge as soon as you light it for the first time.

Step 3: Suspending the Form

Setting the paper mache form is by far the trickiest part of build as soon as you begin to pour the refractory, the hollow paper mache form is going to want to float straight up to the top youll need to make sure that the form is set into the body firmly I used a dowl in the nozzle to hold the form in place along with tons of duck tape to keep it from shifting. You’ll Want to take the smaller of your metal pipe lengths and fit it over the entrance tube of the paper mache form with the treads facing out. Position it so that you pour around it securing it into the forge while keeping the threaded section protruding from the form, this is how you’ll connect the blower and fuel supply to the forge.

Pouring the refractory could be difficult depending on the shape of the body you’ve picked. Refractory by definition is very light and foamy if you’ve picked a commercial mix it’ll generate bubbles as it begins to harden. These bubbles will rise and you need to make sure they have a way to escape the form, otherwise they’ll gather and create large pockets which weaken the forge and have no insulating value to them. I cast mine on a little bit of an angle such that any bubbles would make their to the surface. My L-joint body was certainly not designed to hold a liquid, I found that as I poured, the leaks started in places on the L-Joint I was not expecting. It good to have a lot of towels and duck tape handy to keep it sealed as you pour. You’ll want to allow the form to dry for up to two weeks. While the combustion chamber will harden in a few hours after pouring, itll still have quite a bit of water in it, store it in a warm dry place until your sure there’s no residual moisture left. Any moister remaining will turn to steam and break the forge as soon as you light it.

Step 4: Finishing Construction

The last part of construction is connecting the fuel and air source to the combustion chamber. You should already have the longer section of pipe fitted to entrance of the forge and to the blower. You’ll need to drill a hole in the side of the longer pipe to fit the nozzle of your garden sprayer

Step 5: Starting the Forge

Lighting it can be frustrating until you have just the right mix of air and fuel at first. Understand that the types of fuels you’ll be using will not want to burn at ambient temperatures; they need to be sprayed into the chamber while it’s already hot for them to vaporize and ignite. To get your combustion chamber to the correct temperature you’ll need a heat gun and a handful of woodchips small enough to fit through the entrance of the combustion chamber. With your blower disconnected, set your heat gun to the highest possible setting and aim it down towards the entrance of the combustion chamber. After a minute or two this should get the wood chips burning. From here it’s a process of trial and error to get the cycle started. Turn on your blower and fuel sprayer and aim at the entrance but don’t connect it completely yet. Too much air from the blower and the fire gets blown out, too little and the fire suffocates in the chamber, but if you’ve just the right amount of air and fuel the combustion cycle will start to increase in temperature very quickly, before you know it the forge should have about a two foot flame coming out of the nozzle in a very straight cone shape with no soot, and it’ll will sound like a jet engine, at this point you can fully connect the blower and turn your fuel up, the forge will continue to burn this way indefinitely.

What you decide to do with this heat source is up to you what I used it for primarily was to melt down tons of aluminum cans into a cast iron pan then forming them into ingots.

Important! when you want to shut it off make sure you disconnect the fuel first DO NOT TURN OFF THE BLOWER. suddenly turning the blower off at any point while the forge is at temperature will result in the white hot flames from the combustion chamber to reverse their direction and rise up into the plastic components of the blower, destroying it. after disconnecting the fuel leave the blower on for at least five minutes to allow the last of the fuel to burn up and begin to cool down the forge.