Ray Rogers Handcrafted Knives
A Dirt Simple Venturi Burner
If you are a Newbie to forge building and just want to get your feet wet without spending much money then a venturi burner may be what you need. There is a great deal of very good information on the web about venturi design but it is also very intimidating. You'll see where they say every piece must be just right to get the most from your burner - the pipe has to be just the right diameter and length, the venturi must be matched to the pipe size, the aperature must be just so, you need a way to adjust the air flow, the altitude where you live is a factor, you must have a stainless steel flare that is shaped just so, and so on and so on. Scientifically this is all true for optimal performance but for building a Newbie's forge it is extreme over kill. Personally, I don't want to spend weeks researching burner design and fine tuning the burner and I don't want to buy someone else's expensive burner - I want to heat stuff up and hit it with a hammer NOW!
This is all you need for the burner itself, about $10 worth of pipe and a piece of scrap steel with a hole in it. The pipe is 3/4" black iron pipe about 18" long and the venturi is a 1.5" to 3/4" standard pipe reducer. The scrap of steel will hold the gas nozzle. Notice there is no flare on the end of the pipe, just an open pipe. Simple as it can be.
Here's where I got lucky. This is my Big Kahuna burner. It can be used for wok cooking or for one of those big deep frying pots for deep frying a whole turkey. I got it on sale for $50 but even at full price they are usually about $80. The best part is you don't have to scrap the Big Kahuna to use it's gas line and regulator, you can just switch it from your forge to the Kahuna whenever you want. That could make the whole idea more palatable to the lady of the house.
If you don't want to buy a Big Kahuna you don't have to. Any BBQ regulator available from your hardware store that can deliver 10 psi or more will work. Many of the preset BBQ regulators deliver LESS than 1 psi so shop carefully. Shop around for these parts because you could easily spend as much money buying a regulator and hose as you would spend to buy the whole Big Kahuna.
Then, attach a hose to the regulator. If you can get gas flowing out of the open end of the hose you're half way there. Terminate the open end of the hose with some kind of fitting, it almost doesn't matter what you use as long as it's metal (preferably brass). One popular way to terminate the hose is to attach a Tweco welding tip to it. A welding tip will have a tiny pinhole in it but if you used something else you may need to drill a hole. Drill a small hole about a #60, you can always make it bigger if you need to. Frankly, I've experimented some with this and nearly any size will function but the smaller ones tend to be more efficient with the gas.
This is the regulator. Be sure to include a valve in the line. The valve will serve to control the gas flow to the venturi as well as an emergency fast shut off if something goes wrong.
This is my test set up just to see if this thing was going to function. The piece of scrap metal has a hole tapped for 3/8-24 to match the Kahuna's gas nozzle. Again, all that nozzle consists of is a block of brass with a pinhole in it - no magic there and none is needed. Notice also that the gas feed is just held on with bailing wire. The nozzle isn't centered on the venturi, it isn't even sitting square to the venturi and yet it still works fine. This means you can relax, almost anything you do will result in a functional burner.
Eventually, I welded the nozzle holder in place. If you don't have a welder the cross bar could be attached with screws, pins, or even a really good epoxy. Notice that there is no baffle to control the air flow, and still it worked just fine.
Here's the finished burner. The original burner tube was 18" long but I cut about 2" off to remove the threaded end and it still works just fine. A long tube is a good idea because it gets the gas feed well away from the forge body and helps the venturi stay cool. Exactly how long the tube is doesn't matter much.
This is the forge in operation. As you can see, it gets very hot in there. My thermocouple said 1500 F at this point and it got hotter to longer it ran. This means it is hot enough to forge a blade or do heat treating for carbon steels. It is possible that this set up might be able to do forge welding but I don't think it would be particularly good at it. This burner is not terribly efficient with the gas (most venturis aren't) and a single burner is slow to heat a forge this size. On the other hand, it took almost no time to build and it is about as cheap as any other method. Best of all, it works pretty darned good!
A forge is not a toy and messing around with large quantites of flammable gas can be very dangerous! It is YOUR responsibility to exercise due caution and care if you chose to build a forge. Be sure to comply with all local regulations and restrictions. This web page is not intended as a guide for you to use when building a forge. It is merely intended as a record of what I did and as a way of illustrating the basic fundamentals of how a forge works. I am not responsible for what you choose to do with this information.
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Ray Rogers Handcrafted Knives