How to Build a Propane Forge? – A Complete Guideline
I get a lot of questions about Forge design, Forge configuration, and making forges.
So, today I'm going to talk about all the above. The anatomy of forges, burner types, sizes, shapes, all that sort of thing, but once we get through the details, I'll talk about what I think are good Forge designs for particular uses and things that you might want to try if you're interested in making one.
So, first of all, if you're new to this, do you know that at least 99% of modern knife makers in Western countries use propane gas forges? Isn’t it amazing? So why do they prefer propane gas forge?
Propane forges are clean. There's no smoke. No smell or no sparks is flying out to set your shop on fire. They get plenty hot to forge. Well, they're pretty easy to control. And, they're pretty simple.
Moreover, propane gas forges are simple to operate. Therefore, they're not too expensive. You will get readily available fuel. Really, just a lay down that they're the most complete solution to a forge for most modern makers.
But yes, there are some advantages to charcoal and coal, but for most knife makers, propane forges are the best solution. Now the question is how to build a propane forge?
Before I go any further, I want to tell you building a propane forge is not that hard. It's not something you need to be too intimidated about. Trust me!
When I made mine, it was really early in my knife making career. I was pretty nervous about it, to be honest with you.
I was afraid. I was going to blow something up burn up my shop. Whatever, you should take reasonable safety precautions, and there shouldn't be any concern about that.
I made my Forge, which still works fine when I had no tools and completely had no idea what I was doing.
If you're hesitating about making the Forge don't worry; it's not that hard.
The second point, a single tank of propane can blow up your entire neighborhood. So be very, very careful about how you store and use your gas.
If you situate your Forge intelligently, you'll never set anything on fire. That's really not the big danger, but if you have a tank leaking gas into an enclosed space, then really bad things can happen.
Forges also produce carbon monoxide as Doug Marcaida says, "it will kill!"
Now, think, this doesn't mean you need to be paranoid. Therefore, it just means you should only use gas forges in an extremely well-ventilated space, okay! The safety lesson is over.
What Does a Gas Forge Consist of (Shapes and Size)
Generally, there's a metal shell that keeps the whole thing from falling apart.
There's a burner or several burners that provide heat. You'll also need a regulator. And, there's some kind of insulation; that's really about it.
You crank it up. Flame sheets out of the burner; and it gets hot. It's just no more complicated than that.
So, let's start with the overall shape. First, this isn't life or death important. There are box-shaped forges, vertical tubes, horizontal tubes, etc.
There's a logic to these things, and they all have some advantages and disadvantages, but that's not to say that it's really crazy important which size or shape you choose.
Now, if you do swords, long cylinders are nice. Or, if you do a lot of Damascus, you want to design with an easily replaceable floor because flux will eat it up pretty quickly.
Forge should be big enough to handle whatever type of knife or tool you typically make. If you look at the top propane forges, you notice they have enough space to do whatever you need to do. And you want it to operate reasonably and efficiently.
So, many things that drive the Forge's actual shape are driven by whatever a little piece of crap' metal that you've harvested to make the shell from.
Old propane tanks are really popular. If you can weld, making a box shape is relatively simple, so that's pretty popular too.
If I were using a propane cylinder, I'd probably go vertical rather than horizontal. Because, you can put fire brick in the bottom and then replace it fairly easily when it gets eaten up by flux. It will happen if you do a lot of Forge welding.
Horizontal cylinders, you basically have to realign totally. It would help if you had ports on both sides of the Forge so that you can stick blades all the way through.
If those ports are too small, they'll choke off your burners and shoot flames way out of the Forge.
If you have no way of tightening up the ports of your Forge, it won't be super-efficient and will cost more money to operate.
There's no magic formula here. If you have a space that's four to six inches square by 12 inches or so, you'll be able to make nearly any kind of knife imaginable, even knives a good bit longer than 12 inches.
When you're forging, you don't need to heat up the entire knife. You're just heating up section by section the chunks that you're forging.
You want enough internal volume so that you're not sticking your blades right into the bright blue cone of the flame.
They're basically two parts to the flame, and the inner part has a very oxidizing environment, and you want to avoid it because it caused the scaling and decarburization in your blade.
When you're thinking about a forge, just make sure you properly account for how thick your insulation is.
If you start with a 10-inch diameter shell, two layers of ends wall, or K-wool or whatever will knock you down to about five inches in diameter.
What type of Forge should I make?
Now, let me help you through the decision you might want to make. One general point, there is no perfect forge. Basically, there are three things that you might want to do with a forge.
The first is forging itself, the second is forge welding, and then the third is heat treating.
No Forge is going to do those equally well, especially heat treating.
If you really want to specialize in heat treating Forge, it's just going to be quite different from what you would do to do forging and Forge welding.
So for most of us, the question is, what compromise are we willing to make to get us closest to the things that we really want to do?
Therefore, the first question that you need to ask yourself is, what are you planning to use it for?
If you don't want to make big swords, you shouldn't make it much longer than 12 inches.
Now, if you plan to make Damascus, you will obviously need a Forge that has a big enough bore that you can get the billet into it comfortably.
So personally, I wouldn't want to go much smaller than 4 inches square internally. Mine's a little bit bigger than that so that I can comfortably get Damascus billets in before they get all squashed together.
So, the next thing is what kind of shell do you want?
If you can weld, then you can make a square forward shell any size you want.
You can basically make your own version of the commercial box type forges like the NC tool knife maker series.
Or you can do it all with big firebrick which will take up more space but should run nice and hot.
If you can't weld or don't have access to a welder, it's just a question of laying your hands on the right hunk of metal.
Old propane tanks are very popular. Also, water heater, cores big iron pipes, or whatever; in whatever case, you're talking about a cylinder.
Now, if you want to make swords, I'd recommend making a long horizontal like mine. Mine's about 24 inches long, but if you're not a sword guy, I personally would make a vertical with two layers of refractory walls and ceiling, and then a brick or castable bottom; that way, you can bust it out and replace the floor.
So, I have tried to give you a clear idea about how a propane forge is made of. And, you know different tasks require different shapes and sizes. It is not that hard to make.
Therefore, if you don’t have enough propane gas experience, don’t attempt to make one. Propane can be very dangerous, so please be very careful regarding safety issues.