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This is a small forge I slapped together using elements from several designs I have seen on this website. I used a chimney flue and some firebrick I had lying around. I have never done anything like this before but I decided to give it a whirl. I had all the supplies lying around, but you should be able to go to your local hardware store and get them. This is a charcoal fired forge that should stand up to the high temperatures necessary to melt aluminum, and soften or even melt iron and steel.

Materials 
1 section of round ceramic chimney flue (about 10-12 " in diameter)
6 firebricks 
Bucket of chimney cement (or something like it)
18"x8" section of steel sheet metal, fairly thin( you can bend into a tube)
A blow-drier (will not be damaged) 

Tools
Circular saw with diamond glass/ceramic-cutting blade
putty knife 
6"x1"x1" block of wood with a 45* angle cut on one end 
aviator sheers (or any kind of sheers that will cut the sheet metal)

Warning 
When used properly this forge will be producing very high temperatures. Please use caution. I am not liable.
 
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Step 1: Getting Everything Together

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Using a circular saw with a diamond blade, cut an 8" section of the flue. This will be the body of the forge. 
Arrange the bricks on the ground, or a sheet of plywood, so that you have a platform wide enough for the flue pipe to sit on, with a space between two of the bricks for the bellows pipe (a gap about 2") See Photo. there will be brick protruding for the outside, (I used half bricks) they can be cut off or rearranged, or left. your choice.
Take the sheet metal and bend it around a pipe or something round until you have an 18" long pipe about 2" in diameter. it needs to fit into the gap in the bricks so that the end is about in the center of the flue pipe on top of the bricks. Use self tapping screws to anchor so the pipe keeps its shape. Cut out half of pipe inside the forge so air can get inside. Dry fit everything to make sure it works. 

Step 2: Furnace Cement

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Using the putty knife, make a rough bead of furnace cement around the factory edge of the flue pipe. Set aside.
Make sure there is at least a quarter inch gap between all the bricks, push some cement down into the cracks like mortar. line the edges of the gap for the air pipe with the cement, then insert, use some more cement to make the edges flush with the bricks. 
Take the flue pipe and set on the bricks, cemented edge down, and push down for a close bond. 

Using the putty knife and wood block to put a half inch layer on the walls and floor with a thicker bevel where the flue pipe meets the brick. Get the surface relatively even and smooth working the cement till no bits of the ceramic pipe or brick are peeking through. 
put cement around where the air pipe meets the brick on the outside. cement any holes or cracks in the ceramic. The seam where the flue pipe meets the brick on the outside can be cemented too if you want.
Note: it is nearly impossible to get any of this to be nice and smooth and pretty, as long as it is covered and relatively even that is good enough.

Step 3: Firing

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For the firing process, refer to the directions on the bucket of furnace cement, Mine said to gradually increase heat, allowing it to cure to a solid mass, then full firing may follow. I used started a fire of wood shavings and newspaper. Then I used a propane roofing torch speed up the full firing, inside and out, allowing it to harden. I then set the blow drier on the ground with the end in the pipe and prepared to test out my forge. 

Step 4: Use and Enjoy!

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I put some charcoal in with some wood shavings and used the roofing torch to light it. After a light amount to ash appeared on the charcoal I turned on the blow drier and put in some steel. My first creation was a pair of tongs for my new forge. They are kind of crappy but will work for now. 

Step 5: Modify and Improve as Needed

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I will be making modifications and improvements as I use it, I will post everything I do. The first thing I did was put it on an old metal desk as a platform. second thing was take a broken blow drier, take out the heating coils (the use unnecessary power and make it overheat) and rewired it to a twelve volt transformer (so I don't blow the motor). It works well and heats just enough to melt aluminum (with crappy fuel). 

Step 6:

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After having the privilege to attend a class on iron pouring, which branched out into blacksmithing as well, I decided to start working on it again. Som time ago i had picked up a truck tire rim thinking it would make a great forge, I was right, it works great.. i had manufactured a blower with a  sewing machine motor and pedal for airflow control. I used mainly old crap i had lying around, so i wont go into the details of how i mad it right now, but if there is intrest i can post some of the baisic ideas of what i did and the mistakes i made.

Anyways, here are some pics of the forge proper, more to come including in use. 
Great Instructable. One suggestion I'd have would be to replace the homemade sheet-metal tube with a piece of exhaust piping from an auto parts store. They're usually sold in 18" lengths in a variety of sizes and you can get adapters to fit the mouth to your blower diameter.
rimar20003 years ago
Very good work, jadronx! I suggest you to add an air flow regulator. That will be an enhance, and is very easy to do.
jadronx (author)  rimar20003 years ago
Thank you I was actually thinking about doing that as I was using it today.
Henge jadronx2 years ago
You could also add a slide choke on the metal pipe that you could open and close to relieve the air pressure and control the air flow. That's what I have with my maple syrup boiler, similar concept using the ceramic flue, only a rocket stove. Great project, I might build one of my own.
Henge Henge2 years ago
Did you cut the ceramic flue dry with the diamond blade? I need to make a similar cut (the google search lead me here) and I was planning on using my 7 1/2 circular saw and maybe drizzling water on the cut for the dust and heat. What specific blade was it?
In a couple of days I am going to do an instruct able on making a forge for 5$ and my goal is to make a full blacksmiths setup for 20$ so if anyone is interested, I will share what I know. I am very well read on the topic of blade smithing and I am making a second forge for myself to make swords with (mine is small) so I will be most helpful with that.
jadronx (author)  Jestersteelsmith2 years ago
yes please share, i am in the process of building a new bigger one for bladesmithing
If you want to make one for super cheep, I would suggest a dirt forge. The materials needed are really just a shovel, two inch diameter pipe (as long as needed), a drill and a hair dryer (or an old reversible vacuum from a thrift store). Assuming you already have a drill and a shovel, it should cost about five dollars.
You start by digging a rectangular hole in the ground long enough to accommodate the pipe a foot and a half deep and about two or three times as wide as the pipe, then add another foot of spacing to one end of the pipe but keep this one only as wide as the pipe, it will be for the vacuum/hair dryer (or bellows if you have them). Drill sall holes every 3" along the bar in a strait line and duct tape one end shut. these holes will let the air into the fire, so now you are going to place the pipe in the trench with the holes facing up and the open end facing the hair dryer trough thing. Once these tasks are completed , you can surround the pipe with dirt so it dosnt move and duct tape the hair dryer (or whatever youre using) in. Once it is all ready, fill the pit with charcoal and lite it. It will spark when you turn on the hair dryer, but that's normal. Once you get the charcoal hot (it does get hot enough to forge with, so you can just stick with it)
You can now put in your coal or coke. (coke is much better in my opinion