What's wrong with your forge and how to fix it

Atlas Knife Company

Atlas Knife Company

Joined
Feb 16, 2010
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I'm on a number of forums on other media, and kept answering the same questions primarily because those forums didn't have the Shop Talk education that we have here. Most questions boiled down to a lack of understanding why forges and burners work. They simply copied what they saw on a youtube video or someone's (inaccurate) rehash of Ron Reil's page. Still, it took me like 10 minutes to type all this out, and it condenses hundreds of threads on here. Hopefully, the information is up to normal Shop Talk standards.

Thought I would save some time and post this. Let me tell you what's wrong with your knifemaking forge, before you post your video :):
11. Blacksmithing and knifemaking, despite their similarities, have very different requirements for heat control, steel type, flux use, etc.
1. Burner's don't need flares in a forge, the chamber will sufficiently act as a flare. Try it, you'll see.
2. Your burner is too far into the chamber. The tip should not be visible in the chamber.
III. Your burner is too long. The tube should be 6-8" in length.
R. Your forge is starving for oxygen. Your burner holder(port) should be about 50% bigger than the burner tube and should NOT be stuffed with kaowool. This will allow it to get more air and burn hotter.
3. You only need 100k BTU for a propane tank forge, why do you have two or three burners?
4. Forced air does NOT use less gas than venturi or ribbon burners.
5. Coat your kaowool with something, uncoated kaowool is extremely bad for your lungs and it gets damaged quicker.
6. 1/8" coating on your kaowool is plenty, you don't need 3/4". Refractory has little insulation value, it's just protecting your lungs and the wool.
7. Those are hard firebricks. They have very little insulation value. You want to be using soft insulating firebricks.
8. A 55 gallon barrel is a bit big for a propane forge.
Q. A straight down flame is OK for blacksmithing, but knifemaking works better with an angled burner that creates a swirling chamber.
S. Burners should be measured in BTU, not inches. 3/4" or 1" is meaningless with regards to BTU output. A BTU calculator is linked here https://docs.google.com/spreadsheets/d/11obg0EGWLE94tXqIN0zbjtKiargXJGMBB6uSr5H5sJY/edit?usp=sharing
12. Just because you saw someone do it that way on a YouTube video doesn't make it the only way, or even the best way. My way isn't the only way. But I have spent hundreds of hours testing different designs. I have sold over 1500 forges and 2000 burners and I'm just trying to help share my time and knowledge so you can accel in this hobby(Like Stacy did for most of us).

And here's what you end up with if you follow these guidelines:
 
Great little write up of some of te gotchas. I recently did my first forge weld in my Atlas Graham forge, so I can confirm that 100k btu is plenty. Welded up the seams and used a little WD40, but no actual flux needed. I love my Atlas. Only issue I ever had with it was violating rule #2 when I first set it up. Once I backed the burner out a bit everything was golden.
 
Are you truly using 100,000 btu on thoes forges. That seams kinda over kill and wasteful. The only bone I have to pick with your above post is when you say

Atlas Knife Company said:
4. Forced air does NOT use less gas than venturi or ribbon burners.
Click to expand...

From my experience a forced air ribbon burner can not even be put into the same category as a Venturi burner. Not saying anything bad about yours or any one else’s for that matter. But to give you an idea of btu consumption for a ribbon burner. I have settled on running my forge at 25cfh of propane. But it’s pid controlled so it cycles on and off about every sec. So if I had to guess I would say it’s using gas about 2/3rds if the total time. If I was just to run it at 25cfh I would quickly shoot right past 2200° and who knows where I would stop. 25cfh is 62,000btus. That’s for a forge that has the internal dimensions of 12”W x 9”T x 18” deep. That’s just under 32btus per cubic inch. If you factor in the 2/3rds actual run time that’s 21btus per cubic inch. Your forge for exzample is 2.5”x11” which is 43.2 cubic inches, mine is 1,944 cubic inches. You say that it can forge weld and it comes with a 30,000 btu burner. That’s 694.4 btus per cubic inch. So if all burners use the same amount of gas then how come my forge uses over 30 times less propane then yours per cubic inch.

Let me say this, I’m not saying your forge is bad at all. It’s a really nice forge and built VERY well. My above post is just twords Venturi burners in general. But you make a very nice top quality product, keep up the great work.
 
This is the forge I have from Atlas running the 100k btu burner at welding heat.

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That's a great pic. Mind if I use it?

JT, thanks for the kind words. I'm curious, how do you measure 25 CFH propane, and how long does a 20lb tank last for you?
 
You may use it. Apologies for the dirty pool in the background. It had just been opened for the season and was not yet shocked with chlorine. You may want to crop the pic a bit.

Of course I don’t run it this full bore when just forging. It can hit forge temps plenty fine at lower pressure on the regulator. It also will turn down nice and low for heat treating:
 
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Atlas Knife Company said:
That's a great pic. Mind if I use it?

JT, thanks for the kind words. I'm curious, how do you measure 25 CFH propane, and how long does a 20lb tank last for you?
Click to expand...

I don’t use 20lb tanks as thy are to small for my needs. I use a 100lb and have a 50lb for when I don’t want to drive the truck to town to fill up. From all my research propane has the same conversion factor as carbon dioxide. So I just use a C02 flow meter that has a needle valve for adjusting the flow. In an old post I stated that with the doors closed up and idling along and holding 2000° I was only using 11BTU per cubic inch. This does not support having the doors open or heating steel. But the 25cfh seams to be a happy medium when the forge can settle down and still has all the balls to really crank the heat. The problem I did with burners and blowers is yes the more gas you inject the more heat but your also inducing a lot more air. For a pid controlled forge we just cycle the gas. So if your running blower like crazy then the forge will cool down fast once the gas cuts off. So dile it back a little and it smooths out. I will do a test tomarow. I will weigh my tank befor and after forging and can have an actual solid number for you.

I think the key to ribbon burners is the super short burner flames. This allows more of combustion to be inside the forge. I have zero dragons breath as it all stays inside. I am working on designing a mini ribbon burner for small forges like yours. I think it could change the game. A 20LB tank which has 172cf of gas would run my forge at 25CFH for 6.88hr so with the solonoide control it’s a tad more at I’m guessing 8hrs. That’s crazy if you consider that with a Venturi you would never beable to run a forge that size off a BBQ tank.
 
OK, now I think I understand. Apples to oranges, or in this case ovens to forges. Kilns can run at 3KW and reach 2000°F, which is only about 10K BTU. It has nothing to do with being a ribbon burner, but everything to do with forge design.
 
I think you might have misread what I said. With it buttoned up tight I can run at 11cfh of gas. When the doors are open and I’m forging and heating steel I run at 25cfh this is WAY more heat then I actualy need but becaus I use a pid to don’t use more then I need.
Atlas Knife Company said:
OK, now I think I understand. Apples to oranges, or in this case ovens to forges. Kilns can run at 3KW and reach 2000°F, which is only about 10K BTU. It has nothing to do with being a ribbon burner, but everything to do with forge design.
Click to expand...

I think it’s reverse then that. I think it has everything to do with being a ribbon burner. Not that the burner gets more heat out of thin air but alows complete combustion of the gas inside the forge. We all know that with a flame the hottest point is not right where it comes out but further out. I think this holds true with forges. With big burners the hottest part of the flame is further out then where the forge wall is. This then pushes the hottest part right out the opening. This is all just conjecture but seams to hold true. The big plus is the super short flames of the ribbon burner. Thy are only about as big as a big candle flame. Now I’m just assuming but I would think having the short flames far away from the wall you are now heating with radiating energy. Not energy from the actual flame contacting the forge walls. I think this is why ribbon burner forges are so even. It’s like you popped a little sun in there and it’s shining on every surface. When my forge is running and soaked every surface inside is heated evenly. even the bottom corner right to the left and right of the burner. The forge is square inside so it’s not the flame swirling back around and heating that area. Now the far wall directly across from the burner is a shade brighter but not much. The flames are not reaching that wall as that is 12” from the burner which is a long way for a small flame.
 
hey, new theory and ideas are great. You never know what will actually work until you've tried it yourself. Before then, you only think you know.
 
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