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Oval Forge Design Questions

Robert Simmons

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Greetings and Pardon the wet behind the ears, I am new to the blacksmithing and forge construction -- as well as these forums. I have been doing a great deal of research on building a forge and I have run into one question that I was hoping you all could answer for me.

First, let me tell you about me. I am a Software Enginner by trade, welder and fabricator by hobby and newbie to blacksmithing. I intend to graduate up from using my OA torch to heat metal to a propane fired forge as the OA torch is a horribly inefficient way to heat and inconveninet as well. I have researched various fforge designs and it seems round is the predominant forge design for reasons of convection. However the problem is I would like to do some metal work that might be a bit wider than might fit in a round forge. So here is my thoughts on the matter.

Since I will be forging in my garage in suburbia, I have to have an indoor forge. I have hordes of ventilation being that I can open the door if need be ans I also have a 10cfm fan in my roof with a large opening intake in the wall. Anyway for the reason that I will be working in the garage as well as efficiency I want to make a well insulated forge.

My plan is a two Rex burner forge with 2 inches of KAO Wool on the outside and the KAO Wool encased in 1 inch of refractory cement (castable). I had thought of reversing that but I am somewhat concerned about KAOwool ceramic fibers (mesothelioma in 15 years doesnt sound fun). Finally I woudl coat the inside with a refractory coating like ITC 100. Ok now the questions:

1) I had thought about building an oval forge to maximize lateral space and yet keep down volume. Would there be any problem to doing that? Would I get poor convection?

2) I had thought of setting the burners on opposite sides of the forge near the top but placed so that they would blow along the walls in an effort to get something of a heat cyclone going. Good idea?

3) When casting the forge I have a complex design where the KAO Wool is encased by the castable, I had thought of casting the castable and then slipping the cast into the metal shell after i wrapped the castable with the KAOWool. This would make casting easier, endure I dont crush the KAO Wool, promote drying of all water and any number of benefits. So consider the cast would have a 2 inch lip on each end and the KAO Wool blanket would wrap inside that lip and the whole thing would be slid into the metal shell. After the cast is in, I would weld a lip around the edge to keep everything in place. The tolerances would be tight to insure a tight fit. Am I out of my mind or does that sound viable?

4) I will be using T-Rex burners for the forge and I was considering mounting them a bit back from the actual foge chamber, about 18 to 24 inches and then having a tube that directly intersects with the forge. To accomplish this I thought of taking oversize steel tube, lining it with 1/2 inch castable refractory and the end of the tube would allow me to mount the burner with the appropriate set screws. Good Idea or not?

Thanks a bunch for your time in answering. I appreciate it.

-- Robert

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I built an oval cross section forge and found it very hungry, so much that I could not afford to feed it. The large flat bottom does interfere with circulation, and takes a good time to heat. I have since taken apart that forge and built a much smaller forge. I built a tiny mailbox 1 burner to keep fuel cost down and have high heat. (about 150 cu inches)

If you need to heat odd shapes consider a shepherd's crook arrangement with a slot down one side. You can make a plug to close the slot for when you are working on smaller items.

Whatever you decide to do remember to think about insulated doors that can be partially closed. Having several operating positions is helpful. Using castable/rammable instead of welding the lip will be more durable since the steel will flex in the heat and erode.


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Having the burners opposed is probably not a good idea if you are working on the "swirl" effect---it's not convection BTW but the impulse of the pressurized gas and the burn. Convection is what you get after you turn the burners off! (and is why top mount burners generally are not a good idea, esp as hot exhaust goes *up* and you DO *NOT* WANT TO RE-RUN EXHAUST THROUGH THE SYSTEM!)

I strongly suggest you design your forge for your typical usage and think of using a stacked firebrick forge for those "odd" times. Just like you buy a car for daily use and when you need a large truck you go and rent one for a day or a week! A clamshell design with a blockable slot along one side is a good compromise. When I need to fit a larger piece in I often stack firebricks in front of the open door and make a slot forge that way

Also how will you keep the castable from crushing the kaowool? Pillars? Flanges on the end will not do it as it will crack over time!

Having the burners away from the forge seems rather odd and inefficient; any particular reason why?

Ventilation unless it's blowing over the anvil it's hard to have too much! I use 2 10'x10' roll up doors on opposing walls along the typical breeze path and even in the winger have *both* of them open!

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There are probably as many forge designs as there are blacksmiths who make their own. Many work well and most meet the needs of the designers. Take a look at the forge below. This design has all the suggestions that Phil K made and allows me to work on projects larger than the heated area and may meet your needs with a single burner forge. I weld channel on the ends of a pipe so I can use soft fire brick on the ends of my forge (cut them so they will fit and can easily slide in the channel. I use the channel (not just stacking them) because I work in limited space and need to move my forge around occasionally (I have it mounted on a pedestal with a round base so I can roll it out of the way when I'm not using it). I can open the forge as wide on the ends as I want to. I also cut a slot in the side of the forge (and weld on a shelf) as shown so I can, when I need to, put projects in from the side.... When I am just working with iron that will fit in the end of the forge, I put a soft fire brick on the shelf and slide it in (be sure to be able to slide the brick in far enough to cover the entire shelf... and more).

Soft fire brick need to be considered consumables, because they occasionally need to be replaced. They can easily be cut with any type of handsaw.

Cut the slot BEFORE you weld the channel on the ends. Drill small holes and use high-heat wire to hold the koawool in place.

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post-585-000523200 1278913433_thumb.jpg

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