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what are some good dimensions for a gas forge?


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I've been working with a coal forge for a few years now.

But, I've decided to switch to gas as to not torture my new neighborhood with coal smoke.

I do a bit of everything now and then so I'm having trouble deciding on decent dimensions for a forge body that will give me a good compromise between size of pieces that can be worked and amount of fuel (& number of burners) required.

Does anyone have any suggestions on a good size for a general purpose forge?

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Appropriate to the size of your work?

If you are working wide scrolls, 4x8 inch stock in a power hammer, small stuff that rarely exceeds a small envelope, small stuff in a considerably larger envelope, you will want vastly different forges.


BTW building additional forges of different sizes is easy after building the first. Start small and cheap.

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I agree with Phil.... there is no one size forge that fits all needs. I have built many forges trying to get there.

For small work, I have evolved to the forge design in these pictures. It is simply an eight inch section of a large oxygen cylinder (eight inches in diameter), with a slot cut out of the side (with a table), and 3 inch "C" channel welded on the ends so I can use soft fire brick for sliding doors. A cylinder can be cut into an appropriate size and configuration with a zip disk. If you can weld, you can easily build this forge. Proper lining is the most important aspect to having an efficient forge. If your forge sits on a metal table, you could just sit bricks on the table for the end doors. If you do use the "C" channel for sliding doors, the bricks can be shaped with a farrier's file and/or easily cut with an old hand saw.

A project can put in from the ends (passed through if necessary). A larger project (like a scroll) can slide in from the side. The soft fire brick can be easily pushed (tongs or rod) to open or close the end openings. I use a set of special (light) tongs to take the brick off the side shelf to gain access to the side entry.

The small round forge is mounted on a pedestal with a round base so I can roll it out of the way when I'm not using it.

I recommend one change from the pictures.... The burner should be angled toward the other side, rather that toward the side with the opening.

For work that won't fit into this forge, I use a bed of soft fire brick for a forge floor (on a metal table), then place additional soft fire brick to build up walls for a forge the size I need. I have a flat top (six fire brick bound together with a frame) with two burners I sit on top. Sides have openings as are appropriate for any current project.



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What you're looking for isn't really out there, there is no RIGHT size forge. What you'll need depends on the size or quantity of the work you need to put in it. Dave has a very nice design.

Some years ago while I was looking for the same magic answer a friend and I got into a discussion on another fora, E-mail list actually. Anyway Ralph and I kicked a bunch of ideas around with much enthusiastic help from other list members. The most versatile we came up with is a "brick pile" forge. Your basic pile of fire bricks under the table/bench you pile in the size/shape you need with as many burners poked in as necessary to provide the right heat.

Ralph and I are typical tinkerers, nothing escapes "unimproved". What we came up with is a refractory table, a matching sized refractory lid on a jack and a pile of firebricks for sidewalls. Yeah, we didn't escape the pile of firebricks, you can't really have too many you know. So, how it works is pretty straight foreward.

Jack the lid up enough to place sidewall bricks where you need them, making sure enough burner ports are clear to get enough heat. Lower the lid and you're ready to cook. My burner gas supply is through a manifold so each burner gets it's very own 1/4 turn ball valve. NO gate valves, they are more prone to leakage, propane is a very reactive gas and requires the right kind of rubber to survive for long. This especially counts for your supply hose! Okay, besides ball valves being more propane resistant (buy propane rated valves!) they are FAST, all you need is 1/4 turn to shut the gas off in an emergency. They don't work for doodly to adjust gas flow but that's what the regulator is for.

Anyway, once configured I toss a bit of burning paper in the chamber and slowly open the valve. Poof it's burning, a little time and it's to working temp.

These are a couple pics, one shows the jack, I used a scissor jack because that's what I'd salvaged, the other is all four burners running in a test run. It's also evolved the lid is no longer light firebrick, it's pleats of Kaowool and the whole interior is liberally coated with ITC-100.

ITC-100 reflects IR much better than firebrick or other refractories so more heat stays IN the fire chamber. It's also a LOT less susceptible to hot fluxes. Molten borax is caustic and caustics go right through silicates.

Anyway, this is an early incarnation, it's evolved in the last couple years and will again, I just CAN'T stop tinkering!

Okay, rule of thumb for burner/volume. It takes one properly tuned 3/4" burner to efficiently heat 300-350 cu/in to welding temperature. Convert to metric is you wish, I'm an old fart and ain't agonna do it for ya. Burner size is based on the bore's throat diameter, not necessarily the tube. By bore I mean the narrowest part of the tube, usually closest to the air intake ports. So, calculate the cross sectional area of the throat of the bore, Pi x r2 yes? A 1" throat is 2x a 3/4" throat and a 1/2" throat is half a 3/4" throat. This'll let you calculate how many burners you're going to need darned accurately. Of course you can tinker till you get what you like, it's a blacksmith tradition you know.

Frosty the Lucky.



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