I am going to be building a forge soon and I found the plans that I want to use, I just have a couple of questions. What thickness of metal does the firebox need to be? Is 2" of kaowool better than 2" of refractory cement? Does the refractory cement need to have a rating higher than 2000 deg?

The wall thickness can be pretty thin. Many people use freon tanks, others use pipe and still others use square tubing. I would say that anything 1/16" or thicker would work just fine.

2" of Kaowool -vs- 2" of castable? Depending on the grade (temperature rating) of each you buy will give you your answer. Castable is more durable than kaowool. I have one with Kaowool and one with castable. The one with castable is my favorite.

I would recommend a higher rating than 2000 degrees definately. Especially if you plan to weld.

My personal experiance is that an equivilent grade of Kaowool is a better refractory then castable or fire bricks. The floor of my forge is 1" of Kaowool with 2" of fire brick on top. This gives me a pretty durable floor, but I needed to add that 1" of Kaowool to maintain a welding temp.

Another thing you will want to look at is coating your refractory materials with ICT-100. It's a ceramic slurry that greatly increase the efectiveness of the refractory lining. It reflects 80% of IR back into the forge. If you use Kaowool, ITC-100 wil also act to bind the surface fibers (a good thing).

With 2" of Kaowool coated with ITC-100, I can safely grab the outside of my forge while it's running at welding heat. (note: I don't recomend this with your forge)

Scott B. Jaqua

Kawool will heat faster but won't last as long as castable.

Castable will take more abuse, if you do any welding the flux will eat the wool like a 3rd grade kid on cotton candy. I have a little 8" forge lined with kawool I use kitty litter on the floor to soak up the flux. Kawool is a consumable, meaning it has to be replaced from time to time.

Part of the answer to your question is how much do you forge?

If you just do a couple hours at a time kawool makes sense, it heats quick and is light to carry around.

The castable takes longer to heat up but if you are going to use 8 hrs at a time i'd choose the castable. My .02

I agree, the more you weld with it, the more you will need the catable stuff.
2"-3" is plenty per side which ever you use.
The shell just holds the form, thickness is not a real concern unless you move it around a lot.
A 10"-12" pipe is perfect, I use 12".Freon cans, 5 gallon (metal) cans,even coffee cans will work. sheet metal can be rolled as well.

If one uses sheet metal to form body for a forge wouldn't it be better to stay away from galvanized material , especially if using the castable, because of the heat transfer to the material and the potentional poisioning from the galvanized fumes.

Just concerned.

I would agree with that Mike.

I am not sure what temperature galvanized metal starts to produce fumes but there could easily be enough heat through the forge to get it going. I doubt if Geno meant to use galvanized but someone that does not know might try it. Thanks for pointing it out.

Thanks Mike.
.....DON'T USE GALVENIZED SHEETMETAL.....
(or brass, or anything with zink)
Carbon steel works fine, S/S works best and is prettier.

Sometimes I forget that not everyone is used to dealing with these hazards(zink fumes and such). Thanks for the reminder.
Work safe. Have fun. Be blessed.

If using a forge for primarily welding, is a forced air better than a venturi? What are the typical gas flows for each to maintain welding heat? I have a forge I'm finishing up that will have about a 6" diameter x 13" length on the interior. I originally wanted a venturi style because I'd like to take it places where there might or might not be electricity for a blower. I had thought about making another fixture that could be switched out that would be a blower/gas assembly. Is forced air/fuel really needed for welding? I currently use a small coal forge, but am really sick of coal.

Don

Think of it like a big torch.
When you light the gas, you have instant heat, but pop on the air and it becomes a new animal all together.
I believe it gets hotter, its faster, and easier to control.

The venturi advantage is in the heat treating phase. It gives a slower, but more even heat.
The air fed systems can easily warp a blade from heating one spot too quickly.You have to move the blade around constantly to heat it up evenly, or put it in the swirl itself(which simulates the venturi anyway)

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..................KIDS - DON'T TRY THIS AT HOME.....................

In one of my earlier experiments with building forges, I built one to accept an oxygen boost, which is just a short blast of oxygen to peak the heat(about a 5 second blast).
It worked-Oh too well. It scared the !@#$%^&*()_out of me.

Moving air is plenty guys, OK?

The venturi is fine for hobbiests, general forging, and mokume.
If you want to weld, I prefer the air fed.