Two brick forge designs

[Atlas Knife Company]

Thanks to Dave Breese(Iowashtr), I just got 30 9x4.5x3" firebricks and a box of 2" thick inswool chunks measuring 18" x 16". I want to make a steel framed forge using a couple bricks cut in half and wrapped in wool with a sheet metal and angle iron frame. First, I have a few generic questions:

1. How tight should the inswool be squeezed in there? Should it stay at a loose 2" or press it to 1" nice and tight?
2. What shape should I cut in the firebricks? Round is easiest, but would a flat bottom work better? Square with X-shaped grooves in the bottom to let heat underneath? Triangle with the burner at the top? Upside down mushroom?
3. It's going to be 12" long, can I mount a burner inside or should it just shoot flame from the JTH7 into a hole in the side?
4. Do I need to cement the bricks together or will the wool and frame support it well enough?
5. I plan on mounting my anvil on a 6x6 post in the back yard a few feet from the house. Can I leave the forge outside with a plastic bag over it or will the freeze/thaw of the weather destroy it?

 

[javand]

I can only give an opinion on the inswool question. The insulating factor of the medium is determined by the amount of dead air it traps within the structure. Compressing excessively a specific volume of insulation into a smaller volume will generally decrease the insulative value, following a semi-linear curve to the point of almost null value when fully compressed.

The ceramic, or zirconia fibers present in the inswool doesn't provide insulation, it simply provides a method of withstanding extreme heat, it's the decompressed volume of trapped air space that you want.

In other words, don't compress it if you don't have to. The more you do, the less effective it is.


Cheers!

 

[Stacy E. Apelt - Bladesmith]

1) don't compress the wool. Applying a rigidizer is a good idea.
2) The chamber should be a tube with a flat floor. The floor should be about 1/2 the tube width.
3) If using a torch, have the flame directed into the forge through a hole, but not actually sticking in any. The best choice would be to build a simple small venturi burner. If a burner is used, the flare should be flush with the chamber wall. You can cement it in place with refractory cement if you wish.
4) They don't have to be, but it won't hurt either.
5) Get some BBQ grill covers from the hardware store. Cover the anvil with one and the forge with another. My anvils and forge has been outside for years and are fine. I even have the big buffer mounted on the shop deck and covered .

 

[Atlas Knife Company]

Rigidizer? I was worried that if I just put the bricks in soft wool that it would move around a lot.
Half the width of the tube? If I get a 3" hole, have a 1.5" flat floor. Or should it be shaped more like a D?

 

[Brian Ayres]

I got a case of soft(type23) firebricks for free from work. I made a quick 4 brick forge from 4 bricks stacked and drilled out with a 2-1/8" auger bit. I drilled the torch hole in the side. I learned a couple of things with this...

MAP gas works, but not well. I used by acetylene b tank torch and it worked better, but had a hot spot and the entire forge didn't heat up well.

I should have drilled the hole at more of an angle so the flame would swirl and centered the hole(I drilled it too far back). Also, 4 bricks isn't really deep enough, or hot enough with a MAP tank.

I'm making 2 forges with Zoeller type venturi burners with Inswool, Plistix from Wayne Coe and castable refractory because I felt I was wasting time and fuel with the firebrick forge without a bigger burner.

I guess from my (limited) experience I'd make sure you had a good burner to start.

 

[Atlas Knife Company]

Thinking about 8" steel pipe, wrapping the bricks in inswool. Should be the easiest design to fabricate while still using the free inswool. That would give me about 3/4" inswool at the corners and almost 1 3/4" at the sides.

 

[Salem Straub]

Why not just make a forge out of the 8" steel pipe, using the inswool for a liner, and omitting the bricks except a split one as a floor? Then build a little venturi burner, as Stacy says. They're pretty economical on fuel and easy to build, and you'll grow out of it much less quickly than a little torch forge.

It doesn't have to be rocket science or expensive, you can do things like omit a burner flare or even a mounting aperture, just weld the burner tube to the forge body and form a flare in the kaowool, then rigidize. You don't really need MIG tips for jets, or a perfectly concentric jet/burner tube. Pretty close is often good enough, if just trying to get a forge together quick and on the cheap. Use an old acetylene regulator for the line, yard sales will sometimes have them.

Ron Reil's page on the ABANA website is great for building quickie burners.

 

[Atlas Knife Company]

Yeah, I picked up some 8" steel pipe this morning and realized that the bricks were almost pointless if I used the inswool around them. Although, if I used the bricks I don't need to rigidize or coat with anything? Speaking of, what do I coat the inside of the wool with? I only have a little bit of satanite. Can I use regular refractory cement from Menards?

 

[Brian Ayres]

Yeah, I picked up some 8" steel pipe this morning and realized that the bricks were almost pointless if I used the inswool around them. Although, if I used the bricks I don't need to rigidize or coat with anything? Speaking of, what do I coat the inside of the wool with? I only have a little bit of satanite. Can I use regular refractory cement from Menards?

http://www.arscives.com/bladesign/forge.tutorial.htm

http://knifedogs.com/showthread.php?16064-Build-a-Gas-Forge-Tutorial

Here are a couple tutorials on forge builds.Look in the info for newbies sticky. I think there's more there. You Must have a rigidizer on the Inswool so you don't breath it. Also, buy Plistix from Wayne Coe, or find ITC-100 as an IR reflector. I'm finishing 2 forges this week. One is an 8"x12" steel tube. I lined it with 2-1" layers of Inswool, then am coating with 2600 castable refractory cement, and finally coating with Plistix.
I made 2 burners similar to the ones in the first tutorial, but used a parallel fitting(wye) instead of the tee....