Scrap Metal Coal Forge




Introduction: Scrap Metal Coal Forge

Thanks for checking out my first Instructable!

I had made a forge/smelter recently, but it wasn't terribly easy to only heat up a specific part of the piece I was working on due to it being really tall. Look for that Instructable soon.

I had tried using a metal fire pit as my forge, but didn't want to modify that with an air hole, so it didn't get as hot as I needed. I decided it was time to make a proper forge.

I'm lucky in that I get to play in the school's machine shop whenever I want. I happened across a bunch of free scrap metal from a friend, so I figured this was a perfect opportunity to build my forge.

Step 1: Layout

I had a piece of 1/8th plate that was roughly 24"x24". I decided that I wanted it to be 3" deep to hold a decent amount of coal. I marked off 3" from each side with some soapstone.

Step 2: Cut the "Belly"

I've seen where people would use a brake drum for the middle. I didn't have a brake drum handy, but I did have a section of an air tank that was 9.25" in diameter. I'm not for sure what this part is called in a real forge, but I'm calling it the "belly". I figured that 3" would be a good depth for it.

Step 3: Cut Out the Belly Hole

Once the belly was laid out on the plate, I went to the grinder. I had never tried cutting a circle out of metal with a grinder, but our plasma cutter is out of commission at the moment. I was inspired by Jimmy DiResta for this part. He made a jig for cutting out perfect circles with an angle grinder. I didn't want to spend the time making a jig, so I just went for it. It only took about 10 minutes to cut it out.

Here's Jimmy's video of the jig. If you haven't watched all of his videos, be sure to subscribe to his channel and watch all of them now.

Step 4: Cutting Corners, Scoring Lines, and Bending

After the middle was cut out, I cut out the corners. Then it was time to score the folding lines. I took the piece to the vice first, but because I didn't score it enough I had to move to the brake. I accidentally tried to bent it the opposite way of what I wanted to, so when I tried bending the first fold back the other way it snapped off. The rest of the folds went pretty well, so it was time to weld it up.

Step 5: Welding the Seams

Not much to point out here. Just weld along the seams. It really doesn't need to be welded all the way around like this one. Due to the way pieces were bent, the seam was on the outside, and I didn't trust it too much, so it was welded all around.

Step 6: Air Intake Holes

I decided just to use the belly as the air grate. I just used whatever bit was in the drill press at the time, as I didn't really want to walk to the tool room to get a different size. I'm not for sure how well it will do. I may need to either add some more holes, or plug some up.

Step 7: Air Intake Pipe

I needed a way to get air into the forge. I really didn't feel like cutting and welding some square tube to make the bend. I found a piece of 1.25" diameter round pipe that would work perfectly. I used the pipe bender to get a 90°-ish bend. I thought the pipe was a little small, so I cut a section of 2" and 3" pipe to make somewhat of a funnel shape. The funnel was welded together, then welded to the bottom plate of the belly.

Step 8: Welding the Belly to the Air Intake, Welding Tabs, and Welding Legs

I forgot to take a picture of the belly being welded to the air intake, but you can guess what it looked like.

I wanted the belly to fit flush on the bottom of the forge, so 3 tabs were welded on the top rim of the belly.

I had some long sections of .75" diameter re-bar, and thought they would work perfect for legs. I wanted the forge to be a total of 36" tall, so the legs were cut at 33" long.

Once the legs were welded up, the belly section was fed through the hole.

Step 9: Finished!

The whole build from concept to finished product took about 5 hours. I had a lot of help from a friend who did all the welding. We ran out of 75/25 mix for the MIG, so all we had left was stick. I am terrible at stick welding, so I had him do it all. (I did try a couple welds, and yes, I was terrible at it)

I think I will add a shelf on the bottom and a rod to go around the edges to hold tongs and hammers.

If you have any questions, post them and I'll try to answer all of them.

Thanks for looking and be sure to vote if you like my Instructable!



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    19 Discussions

    Is there any particluar reason you used a cirlce for the "belly"? Im planning on making a forge of my own but i dont think i could cut out a circle. Would a square "belly" work instead? Cool instructable.

    2 replies

    I was thinking the same thing, more so for simplicity than anything else.

    im building a forge might use these plans

    The traditional name for the depression the lit coal goes in is the firebox. It's also often called a duck's nest. And having an ash vent at the bottom below the air input as suggested by stoobers is normal for a coal forge, less for the flyash and more for the clinker.

    It would be better if you would have put clean out with a flipper valve open to clean out and closed to blow air into the fire box

    I do have a tip for how you bent your plate. I have been planning on doing an Instructable on this technique but haven't had a project to demonstrate it yet. You scored the metal by cutting through it partially. My suggestion is to intermittently cut through the plate along the 'edge' to be bent. Basically reducing the overall width of material you are trying to bend. So instead of bending 12 continuous inches of steel, you may only have to bend two or three. Then once you have completed your bend just weld the cuts shut. Sorry I don't have any pictures to show how to do this, but this is the best I can do for now.

    1 reply

    where did the like button go? this is a method I have used many time combined with scoring, cutting all the way through, makes bending without a brake very easy when working with metal plate.

    Good build!

    Here are my 2 cents:

    The square air tube under the perf plate should be about 1 1/2 feet long, with a swivel cap on the bottom, or a flap of some sort. The curved air tube should join this square tube right in the middle (no need for the curve). The perf plate should be replaced with a cube of steel that can rotate around (or skip the cube).

    The reasoning:

    Coal makes lots of ash (fly ash) and it won't burn.

    So you rotate the upper cube and it dislodges the burnt out coal and dumps it down the square tube. Then you use the swivel cap on the bottom of the square tube to dump the build up onto the ground. If you are willing to scrape a lot, you can skip the upper cube, but you should have that bottom swivel cap or you will plug up the air channel.

    1 reply

    Doing this you loose a lot of the benefits of using a coal fired forge first of with a constant running air source that prevents the vent holes from plugging the ash acts as an insulator and keeps the heat in the forge and prevents it from being radiated away by the metal forge., Second, the ash acts as a secondary heat source keeping the coal in a gassing state, creating a hotter bed ( due to its ability to hold heat not due to burning) And of course quenching a hot piece of metal (iron or steel) in a bed of ash holds it at temp and slows its cooling down substantially making it more malleable at lower temperatures, easing the effort needed to work it. It also allows you to hold it at a hot temp with hot coals on it to control the formation of the crystalline structure of the metal allowing better control of the hardening of the metal when you quench it. I wont get into the physics of adding more carbon into the steel, which makes it harder when quenched and numerous other tricks that are lost with "ashless" forges that have come from technology, be it by making forges out of metal that allow ash to be cleared or the use of gas fired forges. The fact is the legendary Toledo blades and Samurai blades were all forged with coal ash in place. These blades started out as almost pure pig iron and the carbon and other elements that made the steel was literally worked into the blades from the coal and ash in the forges that were used to make them. Today we depend on foundries to supply our "premixed" metals for the steel we use. This is just one more step away from our historical methods that have generated what we have used to make the tools that have allowed us to make what we have today.

    It is one of Life's finest ironies, stepping back in technology to learn how to make the better mousetrap.

    I want a forge but umm.. what does one do with a forge?

    1 reply

    Anything you want to. Give a blacksmith something something (metal) to hit, something to hit it with, and some way to heat it up (forge) and he will make everything else he needs.

    @seamster Thanks! Not yet. I'm waiting on my coal to come in. I'll post a follow-up when it comes in.

    @Metal_maestro I didn't think about that at the time. It is a good idea. ModernBlacksmith designed a small forge with that same idea. he cuts it out on his cnc plasma cutter around 6:45 in.

    This is a great looking project. Any photos of if fired up and in use? That would be neat to see!