Forge Question

[garyleed]

Hi All,

I'm trying to build a small gas forge. I read a few designs on the Internet so I went out a got a 13-gallon air compressor tank it is 24" long and 12" diameter I cut one end off already. My question is how long should I make the forge. I plan to but a 2" or 3" of insulation in the forge. Any help or recommendations are welcome.

Thanks,

[Rich Hale]

Maybe I can kind of help. There are formulas somewhere on here thata help you determine how many btus youi need. and how to determine the area and then find out how many of what size burners you need. The maybe part is because I do not remember where I saw the information. But this I do know, If you have not used a gasser before and especially if you are new to forgeing you will be better off buying a forge new and ready to put to work. I have had the opportunity so many times to speak with folks with home built forges that do not get hot enough that is leads me to this thought. Buy one and go to work. If you choose to build I really do hope all works out well Follow all lpg safety precautions and have fun. Some home builts work really well. Rich Hale

[looper567]

How many burners are you going to use, and what style?
Do you plan on forge welding?
If you use the Reil style burners or the Zoeller style burners you'll need 1 burner per 350 cubic inches of volume.
If you use 2 inches of insulation a 14 inch length will have a volume of 704 cubic inches and would require 2 burners.
I prefer to keep to keep the firebox a small as possible, no sense in heating a large unused space. I also prefer to keep the ratio close to 250 cubic inches per burner, it save a ton on fuel in the long run.
Building your own forge is fine, problem is, there's a ton of info online about forge construction, and a whole lot of it is just plain wrong. It seem if someone is able to build a forge and actually make a piece of steel orange with it, they are suddenly an expert and just must create a webpage to share their wealth of knowledge... be careful!
Use a good insulation. For a cylinder, try 2 or 3 layers of 1 inch ceramic fiber coated with colloidal silica hardener (sprays on like water...), a coating of ITC 100 wouldn't hurt either. Use a good floor material, some dense ceramic refractory splits (4 1/2" x 9" x 1 1/4") work well, are inexpensive, and easy to replace when the flux buildup get to be too much. I don't like the idea of ceramic fiber in a welding forge because the flux will literally melt it away on contact, but if you are using a round design, there isn't many options. You could use a cast refractory, but there goes your efficiency... Cast refractory will suck the heat right out of your forge and you'll struggle trying to maintain welding heat, if you even can get that hot. I see virtually no difference between a round or square forge as far as even heating goes (and I have built HUNDREDS of forges), and a square body gives you a ton of options as far as lining material goes.

[ThomasPowers]

The base piece of information is How long a heat do you need to get on what you plan to work on---you can always add burners to deal with more cubic; but if you regularly need to heat 24" at a time for a scroll or twist then a 16" forge is not going to help.

So what kind of work do you plan on doing and how much needs to be hot at the same time? (eg: swords you really only want to heat 4-6" at the same time except for heat treat which is a special case; while a big scroll may need to be bent in one go as it will be too wide for the forge afterwards.)

[looper567]

Actually, that's exactly why the round design is so limiting. Openings on the ends will not allow you very much access to the firebox. It really is senseless to build a 24" long forge because you may occasionally need to bend a long scroll. 99% of the time you really only need maybe 8" - 12", so you will forever be throwing money away wasting HUGE amounts of fuel. The round forge can be made to accommodate a scrolled piece with no problem. Simply cut a 3" wide door down the length of the forge, that, along with your end openings, will allow you to scroll 12" inches and put the flat back in for the next heat. This will save you TONS on your fuel costs. Use the piece you cut from the cylinder to make a door so you can close off the opening when you don't need it. I've worked very large scale high end architectural ironwork jobs up and down the east coast. We were using a 100lb. Dupont mechanical hammer and a 110 air hammer (Tom Clark's hammers), and NEVER had a need for a 24" long forge, because we had access to the firebox as described above (using the Forgemaster Blacksmith 2 burner model). There was never a case where we were unable to forge a piece because our firebox was too small. I have an old pipe forge in the shop I could take some pics of if you are unsure of exactly what I mean.

[looper567]

This is an old one that's been collecting dust under my bench for a LONG time... But it illustrates my point well enough.

[Pault17]

My first forge was a bean-can fired with mapp. I did accidentally make one forgeweld but didn't find it till much later: now I have no idea how I did it.

my latest forge is a "balloon time" forge fired with a Rex Price Shorty. The sides and rear are lined with 2 inches of kao-wool coated in satanite then itc-100. The bottom is 1-inch firebrick front to rear, with large opening in front small in rear.

I haven't tried to forge weld in it yet, but everything I have worked on, which is to say anything I can fit in or through the cavity, has been worked at a regular bright orange using only 3-4 psi. sometimes as much as 5 when I fill the chamber up.

I have built all of them following directions from here, anvilfire and rex price. I never really did any calculations. I guess I just got lucky:D