forge build opinions

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JasonByers

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Feb 10, 2010
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I want to build a larger forge for everyday use but I also want get to welding temps fast and without running at 20psi. These are the supplies I already have: kaowool, satanite, ITC-100, Mizzou for flooring, and 6in steel pipe. I'm going to buy Darren Ellis' 3/4 venturi burner. Ok this is what I want to do: I want to use the 6in pipe I already have but want a bigger chamber diameter than 4in that two layers of 1in kaowool will give me so I want to use only one layer of kaowool. I'm planning on building it with a front door opening of 4in wide and 3in tall and the same opening in rear that can be closed off. The inside dimensions would be 4.75in (one layer of kaowool, 1/4in satanite then ITC-100) X12in long. This would be around 215 cubic inches. I know I should probably use 2 layers of kaowool but with the burner rating of 350 cubic inches would this forge be efficient enough to weld in easily and cheaply (fuel consumption) only using 1in of kaowool.

My burner port entrance will be determined by the amount of kaowool I will be using since I’m entering straight in from side and closer to the top such as Darren Ellis builds his forges so I wanted to run this by you guys first. Sorry it seems like I'm slouching on the build but 8in pipe is very hard to get here without ordering a lot at a high price and I want a bigger opening than 4 inches. However, if using only one inch of kaowool won't get me to welding heat easy I'll use two. Thanks guys.

Jason
 
I have just one layer of kaowool in my 8" diameber pipe forge lined with 1/4" of satanite and a mizzou floor. I don't have the ITC layer, and I can easily reach welding heat. There is one big difference, though: I have a blown burner. I run at 1 psi give or take, and I can hum along at 1800 all day with the gas barely cracked. More gas and air, and it warms right up.

I'm not sure about the performance of the venturi burner, but the insulatory properties are obviously very important. With the smaller forge and a properly tuned venturi burner, I don't see why you couldn't get there with one layer of kaowool. I guess you could always add an outer layer of kaowool to the forge body for better insulation and temperature stability without sacrificing internal chamber space.

--nathan
 
Bit of a planning issue here: In 6" pipe, one layer of kaowool will give you 4" or less - it goes all the way around so you deduct twice the thickness...

Dave
 
HAHA, your right. At least I'm in the planning stage. I was thinking of building a forced air forge but I like the mobility of a venturi type for now. I actually wrapped some wool inside of the pipe and FOUR inches wasn't all that bad. I just need a longer forge than my Whisper Baby. I'm going to give it a shot with what I have for now if it doesn’t get hot enough with efficiency I'll build another one later. Thanks guys for your help.
 
Did you check with any local well drilling outfits? They often have scraps of 10" and 8" sch. 40 well casing/pipe sitting around. I would go with 8" pipe for sure, 2 layers of Kaowool really helps with a venturi burner. Especially since it seems that this is going to be a welding forge for you.
 
Yep I checked with one drilling outfit here and they didn't have any. There's more around here so maybe I'll check with them. Shoot I'm in no hurry some 8in will show up. Thanks for the help.
 
OK, Let's talk forge design:

No good forge will reach welding temps fast.....and a large one will be slower. A long thin forge chamber with a venturi burner will be very inefficient.

A 6" shell won't make a long forge. It will make a 10-12" long forge at best. Use a 10-12" pipe/shell for a long forge.

A small venturi burner won't reach welding temps efficiently ( or at all) in a large forge. Either use two burners or a large blown burner ( best idea). Burner angle, placement, and flame path is very important on a long forge.

A blown burner is really no less portable than a venturi burner. If there will be no electricity within 100 feet of where you will be forging damascus ( unlikely) you can use a 12 VDC blower and run it from you truck battery. On a welding forge the propane tank is more of a concern with portability that the burner. ( You need a large tank to avoid freeze-up - 100 pounds or larger is the norm )
Basically, a damascus welding forge is not (usually) a portable item. Lots of bad things happen to well fired refractory liners when bouncing around in truck beds.

For welding you need 2" of wool, 1/4" to 3/8" of satanite, and a good coat of ITC-100. These measurements are doubled to get the lining thickness. Thus a 10" pipe will have a 5" chamber.

For a robust and long life forge, a cast refractory liner may be a better option. Cast a 1" thick liner, coat the inside with ITC-100, wrap it with 2" of high-Z wool, and bundle that in a sheet metal shell.
This will take a good while to heat up, but is quite efficient once at temp. For HT this is a superb design.

Raising the gas pressure beyond normal won't make the forge heat up all that much faster. The thermal mass of the lining is the determining factor ,mainly.

A forge shell only needs to be a few things:
1) Metal....and round
2) Able to withstand 500-600F heat
3) Cheap

A trip to a scrap yard ,or a drive around town on trash day will bring many things up that will work. When your brain thinks "FORGE", everything looks like a shell.
Many things will work that are free or very cheap:
Trash can or waste basket- preferably a plain steel can ( before anyone yells, "Not galvanized", remember that the shell won't be getting hot enough to burn off the galvanizing - but ,yes, it would be best if it isn't galvanized )

15 to 35 Gallon oil drum ( check you local car dealer or garage)

Used water heater tank or shell ( free from any plumber)

Used 25 gallon syrup tank ( check your syrup supplier for a damaged tank)

Piece of 24 gauge sheet metal rolled up and pop riveted into a cylinder ( this is how the outer shell of most cast refractory forges is made).

Old water main pipe ( check the water dept.)

Well shell (check the phone book under "Well Drilling"

Cut-off from a metal fabrication shop ( usually free if you explain what you want it for)

Junk yard, scrap dealer, trash dump.....all kinds of neat stuff shows up here.

........you get the idea.

Stacy
 
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OK, I follow everything you said ,Stacy, but one question comes to mind that for me, begs to be answered.
Why won't a 6 inch casing make a long forge ? Either way you end up reducing the chamber to 4-5 inches, So I'm thinking that ain't it. The answer please, my brain hurts from all this research on forges.
 
Honestly I'm really wanting a longer forge than I have now (10in is fine), welding is just a plus. I can always build another for welding later. I have a Whisper Baby and even though I have a back door it's a pain to forge longer blades. I also don't like how the flame is right where you place your stock either. I have another forge I heat treat in, it's also small but keeps good even heat that I can easily adjust. I wanted to build this one to use also for heat treating and give my other to a friend just getting started. I guess I'm asking too much from one forge huh. My design is from looking at the forge that Darren Ellis builds. The 6-HT I think it’s called. He says on his website that it will weld small billets and cable. I'm pretty sure he only uses 1in of wool and satanite with an ITC top coating. I'd like to build one close to his design. I'm a good welder and have all the other steel I need. But if you guys strongly disagree with his design I will build this out of an old portable air tank I have which is 10” in diameter and pack it with 2in of wool. My only concern is the thickness of the steel in the air tank. I want to build a good looking forge that will last. Thanks guys for the time.
 
That last post was mine. I changed my profile name because I'm about to purchase a knife maker profile and wanted my full name. I was on another computer that was still logged under the old profile. Sorry for the confusion.
 
little mac,
A 6" pipe with 1" of wool and the refractory coatings will end up with a 3.5" chamber. From that you add a floor and the chamber gets smaller. On a 10-12" long forge, that will be OK, but on a 24" forge, there will be problems with even heating. If that was done with 2" wool you would have about a 1.5" chamber .

You need enough room for the flame to swirl around the chamber, as well as room for the exhaust gasses to exit. Too long and thin and it becomes a flame thrower.

Jason,
You only need to heat about 4" of the blade to forge. It is poor technique to heat the whole blade at one time. Work your way down the blade a few inches at a time. I forge 36" swords in a whisper lowboy, and can do the HT with it,too, if needed.
A long forge has its uses, but for general forging and for damascus welding, a 16X10" forge with a 6" chamber is perfect.

A vertical forge is a very useful shape,too. 16X12" (7" chamber) will do most anything.

Stacy
 
well now, that makes alot of since. Most of what I've read was for building smaller horizontal forges and 4 inch chamber sizes get tauted like the sacred cow of chamber sizes. The novice engineer in me was beginning to question just how in the heck you could get an effective flame swirl in a 4 inch chamber over 10 inches long. Short answer, you don't.
I'm beginning to think the best thing for me to do is build a HT oven for HT, Anneal, ect and a forge for forging only. As a beginner I got no reason to heat or try to weld more than 4-5 inches at a time anyway. A vert forge might be the way to go, altho I hadn't really give them much thought.
Thanks for your time and patience to help us newbies and keep us in line.
 
Thanks a lot stacy for your time helping us out. I'll follow your recommendation for forge size and forging technique. Good thing I've never had a chance to heat a whole larger blade then. Thanks again.
 
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