Planning out my first forge

[AngryOnion]

I have read/watched the safety hazards related to this. I have a good respirator on hand and am an experienced welder/fabricator. 

 

So I've been reading up on what materials to make a ceramic blanket forge, but wanted to run it by people with experience first. The picture is very similar to what I want to do. As far as the shell on the outside, what sort of dimensions work well? I wanted to start making knives and other small things. I've been looking at using either an old propane tank(potentially dangerous) or air compressor cylinder. Any other suggestions? I've seen these somewhere around 12" diameter, but have no idea on what a good length would be. I was going to have a hole in both sides in case I did something longer.

As for the inside, I was going to do two layers of 1" ceramic blanket, and rigidize them both. I'm not sure how stiff it gets when you do that, so do you heat and dry them out as flat sheets, or put it inside the cylinder and use the burner to dry it out? For the refractory I've seen a lot of people on here using Kast-o-lite, so probably that. If I remember right, it's not the greatest against flux, but I don't know how often I will use any.  Now if I have a fire brick bottom as shown, do I put the refractory on that as well? I'm trying to follow the advice from the pined thread about this. 

 My consolidated notes for new forge builders - Gas Forges - I Forge Iron 

As far as actually using the forge, how close to a stud wall in a garage would be safe if I put cement backer board as an insulator on it? 

Thank you again for all the help guys.

[Mikey98118]

Most people seem happy with a forge shape that is around one-third longer than its diameter, when they have a choose at all. Many people just adhere to the length that the diameter they wish comes with. A non-refillable freon or helium cylinder is the common choice for knife maker forges.

[twigg]

Short version: if you copied the forge in that picture, you'd be fine 2ft away even with no board.

How far you want the forge from the wall depends on how well the flame circulates before exhausting. In my helium tank forge you could safely put it 2 feet from a wall because it didn't leak flame much. In my horizontal ammo box forge, it made a piece of duct 1 ft away horizontally and 2.5ft away vertically too hot to touch because the flame doesn't "swirl" well inside the forge and just goes right out the door. 

After forge geometry what matters next most for flame "swirl" is burner angle. If you follow the approximate angle of that example pic, you'll be fine. That's very similar to my helium tank forge. 

Best tip I can give you is if you use a helium tank, when you cut the ends off take the time to keep your cut line straight. It'll worth the hassle when you go to reassemble. Ask me how I know 

As far as dimensions, I've never worked on a knife that was too big for a helium tank forge. My doors sucked so I had trouble getting curvy shapes in and out but I never ran into a size issue. With those hinged doors in the pic, that forge will feel roomy for knife making.

[AngryOnion]

Are the helium tanks made of steel? Just trying to figure out what I can weld onto it.

[JHCC]

Yes, but it is very thin. I haven't measured it, but I'm guessing around 18-20 gauge. 

On 1/2/2021 at 10:44 AM, AngryOnion said:

how close to a stud wall in a garage would be safe if I put cement backer board as an insulator on it?

You can make your insulator somewhat more efficient -- and keep the stud wall cooler -- if you attach the cement board to the wall with spacers and with the edges open. As the cement board heats up, the air in the gap will get warmer and rise, pulling cooler air in from the bottom. I've known people who've also put a layer of aluminum foil on the wall, so that any radiant heat from the board gets reflected back out as well.