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I Forge Iron

Designing a forge


genesaika

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Alright so I've been reading and researching and beating my brains out on this, but I think I have a plan now. I'm going to make a D shaped forge interior that will be 8in H x 7in W x 8in L. I'm going to be using a 3/4 Mikey burner, which I'm working on building.

Now for some questions. I'm figuring the easiest way for me to build this forge is to get a mailbox and cut it to the length I need. The only one I can seem to find is made of galvanized steel, would it be dangerous to use that as the shell? It's also possible for me to build it out of a regular sheet metal, but the mailbox I found is $25 so it would likely be the cheaper option. The mailbox I found is 25in x 15in x 12in.

My plan for the insulation is to have a double layer of 1in ceramic fiber blanket, rigidized, wrapping the whole inside. Then I will coat it with a 1/2in layer of kastolite 30 and a painting of matrikote. It will be open on both ends with firebricks, also coated in matrikote, to close up the ends. I haven't decided if I'll use a 20lb or 40lb propane tank yet, but I guess that will be based on what I can get the better deal out of.

So any criticisms, advice, or anything? 

Thank you for any help and I will keep with post updated as I go.

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In theory your shell will not get hot enough for it to matter being galvanized.  However that is a theory and one i would recomend against finding out.  Personaly i dont let anything galvanized anywhere near my forge.  Also depending on how you form your D you might be pushing the top end limits for a 3/4" burner.  I might recomend extending your forge to 10" and going with a 1" burner.

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That's my concern, I'll have to compare the prices of getting regular steel and stripping the galvanized layer and make a decision.

As to the size, I an always adjust the width and height to be a bit smaller, or even the length. So take the dimensions as rough estimates, not final decisions. I'm planning on the interior volume to be around 300 - 325 cubic inches. I will not be using a bigger burner because I already have it started and, honestly, I think it's a bit oversized already.

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If you make sure the refractory wraps around the shell at the openings a galvy mail box will be fine. If the outside of the shell turns red hot turn it off and find out what's wrong. Zinc burns at a low orange temp and if you see blue green flames and white lacy smoke, kill the fire and leave the room. Still find something unplated if you can, better safe than sorry and this is an easy hedge on your bet.

Running the numbers you list I get 448 cu', a bit much but if you don't intend to weld it'll reach forging temperature. You can easily reduce the volume for jobs requiring welding by making a floor insert. Cut ceramic blanket, rigidize and coat it with Kastolite. This would be a temporary insert, just lay it on the floor of your forge with a couple sheets of paper between to prevent them bonding at heat. This will reduce the volume to right around 350 cu'. If you put 1/2" of kastolite on both sides the volume would be 320 cu'.

Frosty The Lucky.

 

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Another forge shell option I like even though Mikey doesn't is stainless steel stove pipe. It's a little spendy but comes in many diameters and pretty short lengths. If you need an oddball diameter you can snap different pieces together, for a weird example 10" dia and a 5" dia section for 15".

Stainless stove pipe is strong, there are off the shelf accessories that make construction easy. Wall brackets make perfect legs and burner supports. There are bushing reducers, caps, plugs, etc. easily available. Laying flat even with say 18" between the legs it'll easily support anything you're going to be forging. Well, unless you're making Ship's anchors or tank axles that is. :rolleyes:

You don't need special tools at either. Good tin snips, drill and bits, a hole saw is nice or a saber saw. Pop rivets and or screws is pretty much all you need in your tool box.

If you want a vault (mail box or D shape) you can screw it into a board and bend the overhang flat for the floor. Or just fill the bottom with another layer or so of RIGIDIZED blanket and cover it all with hard refractory. 

Nothing wrong with not wanting to use a salvaged pressure tank or piece of heavy wall pipe. It's too easy to get sucked into the idea we HAVE to use a thing because we have one. I've done that too many times myself, I have a closet full of that brand T shirt.

Frosty The Lucky.

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I'm also leaning away from stainless, ever though it would be pretty, because I want to be able to weld to the shell easily. I don't mean welding the shell together, but welding things to it.

As an update, I found that I can get sheets of 22 gauge mild steel for $10 each so I will likely go with that. I'd prefer 16 gauge or better, but they don't stock it locally. I still might order it online though.

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Another option gene is irrigation pipe.  That os something sold in every town in america big and small.  The only thing to remember with it is its size is OD not ID.  But get a piece of 16gauge 18" and you can easily fill the bottom to make your D shape and reach the sizes you want.

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On 11/22/2017 at 5:42 PM, genesaika said:

I'm planning on the interior volume to be around 300 - 325 cubic inches. I will not be using a bigger burner because I already have it started and, honestly, I think it's a bit oversized already.

You have it right; a 3/4" Mikey burner is on the large size; fortunately, these burners have long turndown ranges. You have a guide plan so far. Remember that vinegar in water is the easy way to get rid of zinc coatings. 

That should read "...good guide plan..."

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