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Need some tips and tricks on building a charcoal forge.


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Hey everyone

I'm just recently started my adventure into blacksmithing and am looking to upgrade my "old" forge (about 2 weeks old). The old forge was plaster of paris/sand molded around a steel pipe with holes drilled in it and surrounded by bricks. A hairdryer and hose was connected to the pipe for airflow. It was a great little forge for my first experiments into blacksmithing but I was looking to make something a little more portable and longer lasting as the plaster has started to crack.

 

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(old forge)

My idea is to follow the same general shape of the old one but I am using firebrick instead. I was thinking of carving out the base of the firebrick so that the airflow pipe (tuyere?) sits recessed into the base (and also to carve a hole at the back of the forge for the pipe to stick out). I also have some high temperature refractory mortar (up to 1600c or 2912f), can I use this to line the entire inside of the forge (including the base around the pipe) so that it will last longer? I imagine placing metal and charcoal into the forge on just the firebrick alone will erode it quite quickly as they are very fragile. The entrance of the forge will likely be covered by another fire brick / regular brick on its side so that it creates a lip / barrier so charcoal doesn't fall out.

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In terms of airflow I am using the same hairdryer. Previously the hairdryer would sit loosely inside a funnel with a hose taped to the smaller opening, the hose is then attached to a very thin aluminium pipe which then went inside the steel pipe in the forge. The reason I did all this was due to the hose originally melting on the forge side and the hairdryer becoming so hot it melted the hose on the other side too. For what ever reason, having it sit loosely in the funnel and adding the aluminium pipe on the other end prevented it from overheating / melting.

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The new design is a little cleaner, with the hair dryer sitting inside a PVC 90degree bend connected to a PVC pipe. the hose is now sitting in a brass hose fitting that has electrical tape around it so it fits snugly in the PVC pipe. on forge end, I now have a bigger steel pipe (I removed zinc plating from both pipes) and the hose just sits directly in it. I am hoping the the longer pipe, which will extend further out the back of the forge than the old one (shown in photo above the new pipe), will not get hot enough to melt the hose. However the hairdryer now gets extremely hot, even on it's cold setting. I don't want to go back to using the funnel as a lot of air escaped but it might have to do for now.

The old pipe just had holes drilled in random areas along and around the pipe (although only half the pipe was above the plaster of paris). Instead of drilling holes all over the pipe, my plan is to use an angle grinder to cut a straight line down the middle of the pipe so the airflow is more consistent along the pipe.

 

Apologies for such a big post, I didn't think I had this much to ask! But I would love any constructive criticism or even advice on what I could do better, what I am over complicating and any better design for my forge. I'm building it in a small form factor just so I can move it around more easily and as I don't have a lot of space in the area where I use it. I would also love any recommendations for a good / cheap option for my airflow! 

Thanks in advance :)

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Take a look at the JABOD (Just A Box Of Dirt) forge threads. Firebrick is kind of overkill for what you're trying to do.

Definitely don't bother with plaster of paris in any forge application. It simply doesn't stand up to the heat.

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Plaster of Paris starts to degrade about 1000 degF BELOW forging tems; so not a good idea and all the idiots on youtube suggesting it should be horsewhipped!

A JABOD is good; you may also want to look into Tim Lively's washtub forge  as they had a lot of good experimentation and results using them a couple of decades ago!

Definitely look into replacing the noisy and too strong hair dryer.  Charcoal takes "soft" air and needs much less "push" to get the air through the fuel---why bellows worked so well for several thousand years with it!

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Portability with a JABOD or JAPOB forge is always tricky because of weight. 
I prefer a simple side blast tuyere to Tim’s as I find it more fuel efferent. 
this is my thoughts and experience with brick, make a rectangular box out of brick the size of one brick, in the US that would be 4” wide, 4” deep and 8” long. This is below the hearth, or in this case more brick to make an area before and  shine the forge to support the stock, then on each side place one and a half or two bricks on each side to make a trench 4” high and 12” long. It’s hard to clean out and you will melt bricks...

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Yeah the plaster of Paris didn’t hold up but it was just a temporary solution as I was just too excited to get started.

Some of the forges in JABOD look really good and easy to make. A lot seem to be quite big which might make it difficult as I have set up shop in our shed ( great ventilation but very little space). I might see if I can make a JABOD forge but in a smaller form factor. Is the box usually filled with dirt or sand?

In terms of air supply, would a little hand cranked fireplace blower or bellows like the ones in the photo work? 

blower.jpg

 

bellows.jpg

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"Just A Box Of Dirt" is generally filled with dirt; preferably low in organics.  They even have been made using cheap all clay kitty litter!

They can be sized to fit your needs.  Most people build forges that are too big anyway. The number of times I have had to tell someone that you only want to heat about 6" of a sword you are trying to forge at a time is a close approximation to  the number of Y chromosome students I have had at the forge.

Not having used either of those air supplies I can't speak of their functionality.  I would ask if the bellows has a check valve so it doesn't "inhale" hot coals through the nozzle in use!

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Subsoil usually dose well, I would say a 24” inch buy 18” box is about as small as is practical with a forge fire about 4” wide buy 8” long with a 3/4-1” ID tuyere. This will heat a 1” bar or less. 
If you use the small wood stove bellows you will need two pumped alternatively as it is not a double bellows. A cross shaped rig can be made that will pump them with only one hand. 

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Ah I see, I decided to take the easy route and purchased a hand cranked forge blower instead. Hopefully that’ll be more efficient and quieter than the hair dryer and less physically intensive than a hand pump.

 

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I am still torn on the tuyere design, the idea was bottom blast using a pipe with a long gap running through the middle ( like in the photo below).
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Charles however mentioned a side blast and that seems so much easier than having to carve out the firebrick and cutting a line down the pipe. Would it work something like how I have it configured in the photo below? ( the pipe will sit much lower, just using regular brick to test it )

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Methinks it would work a little better if the tuyere came in an inch or so higher and at a slight downward angle.

I would also make sure the brick that makes up the back wall (perpendicular to where your air is coming in) is removable so you can put a longer stock in the forge. Think trench, not box.

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I may of got too excited and done a silly, I stuck the four bottom pieces of brick together with mortar (probably reversible right?).

I'll see if I can get the tuyere higher or at least coming in at a downward angle, if not, I'll just have to fire it up an see how it goes. 

In hindsight I am starting to see how the box design might be a bit inconvenient with charcoal. When I wake up tomorrow I might have to do some redesigning :(

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If it's only the bottom 4 pieces you may not even need to break them apart to move the hole. Just make a second one in one of the wall pieces and plug the old hole with something... dirt, mortar, a small piece of brick from your new hole, whatever you have. It doesn't have to be air-tight/pretty so you can fill it with anything so long as it isn't going to burn up on you.

Honestly, before you bother making any changes, fire it up a few times and see how it goes. After a few sessions you may discover other things you want to change or decide that things are fine the way they are. I do think the back wall will be more of a nuisance than a benefit. The nice thing about solid fuel is you don't need to worry about containing the heat like you do with gas. That leaves the fire more open for long, large and/or oddly shaped items to be put in. The more you box your fire in (too high of walls/a back wall, a top) the less access you have to it.

It seems like what you have there will work. Down the road you will likely end up modifying it based on your needs. That's half the fun. When possible, try not to make things permanent until you're sure it's the way you want it to stay. That's one of the reason the JABOD is so effective. The firepot can be molded and reformed in many different shapes and sizes; nothing is permanent.

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With charcoal there's really no need to have the tuyere raised higher than the floor. With coal you want an inch or so below the tue for clinker to collect but with a brick firepot like that it can be level with the floor. Any fuel under the tue is being wasted. Check out the MARKIII jabod thread .https://www.iforgeiron.com/topic/55467-mark-iii-jabod-forge/

Pnut

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Ah I see, I fired it up and boy it was significantly stronger than my original forge, the whole base was basically alight. I was able to take it apart as others have suggested in this thread, a JABOD would be much better! But I'll keep that in mind pnut, I'll see if I can put the tuyere basically touching the floor in my next build :)

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It took me a couple builds before I settled on a good set up for me. It's pretty close to the MARKIII jabod with the exception that I have bricks on both sides of the firepot sometimes instead of just the tuyere side. 

Pnut

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I liked the tuyere higher but as has been said it's good near the bottom. However I highly recommend you pull the pipe an inch or so into the brick and use the hole you drilled as the final nozzle. The firebrick has to take the heat anyway and there's no good reason to burn up more pipe than you have to. Believe me, your forge will consume steel in the tuyere's position like candy.

Frosty The Lucky.

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Hey, little update here :)

I decided to go with a JABOD design and so far I like it a lot. It’s filled with sand and small charcoal bits instead of dirt.

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It’s a lot smaller than most JABOD’s out there as I really wanted the portability to move it around the backyard. The hand cranked fan also works great and I attached it to the side of the box so it all moves as one unit. I honestly don’t know if this will work but I attached a copper/aluminium heat sink from spare laptop parts to the pipe tuyere at the back of the box to hopefully keep it cooler so the hose doesn’t melt. I ran it for about 1 and a half hours and the heat sink got plenty hot but I really don’t know how useful or effective it is. 

the only problem that I have into now is the fire is basically limited to a small area near the tuyere. I have the tuyere sitting basically flush with the firebrick as frosty suggested but I also made it so the tuyere is basically on the floor. I tried my best to get the fire to extend further out but it refused to get any bigger than that. Any recommendations on how to get the fire to be more elongated? I tried heating up some steel to test but it only reliably heats up about an inch.

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Sorry for so many questions everyone but I really appreciate all the help you guys have given me :)

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The way you have it set up at the moment really restricts what you can put in your forge. In your previous pictures your tuyere was coming in from the side. Now it's coming in what I'm going to call the back. In this configuration it's going to be difficult to heat much more than the end of a bar since there is a wall there!

Remove the back wall (again, think trench) and have the tuyere come in from the side again. I'm guessing your fire had burned down when you took the picture, but It looks like you'll need to add a lot more fuel in order to heat a larger area. Fuel doesn't make the fire hot, air makes the fire hot. However, you need to have enough fuel present to consume that air otherwise you end up with a cooler fire, not a hotter one.

Credit to Charles R. Stevens and his Mark I JABOD for the picture.

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He's using bellows rather than a hand crank blower and dirt rather than fire bricks, but it seems this is pretty similar to what you're trying to do. If not, I think this would be a good direction for you to go (even if you're using different materials)..

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What size if the air pipe going into through the brick into the forge?  

Suggestions are to add more charcoal, enough to be almost level with the top of the sides of the forge.  Fuel does not make the fire hot, air makes the fire hot.  When you have more fuel you can then control the amount and shape of the fire with the air.  Gentle air is best.  This can be done with your current set up.

After more fuel, raise the air pipe say 2 inches above the floor of the forge.  Going to the next smaller pipe size will help as it will create more of a forward air blast, and move the fire from the end of the pipe.  

All this should create a fire ball that would fill the gap between the side wall bricks.  The sweet spot of the fire should then be 3/4 up the side walls. The fire should be just a bunch of glowing embers, with no aggressive burning.  Fire does not make the metal hot, the heat transferred from the glowing embers make the metal hot.  

You got a good start, you just need more fire.

side blast forge

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6 minutes ago, Frazer said:

, I think this would be a good direction for you to go (even if you're using different materials)..

I had a setup like that with the box filled to the top and the bricks sitting on top like a Japanese forge and it worked great. Basically two walls just like the forge in the pic you posted Frazer. 

Pnut

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