Forge building advice...

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RANGER295

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Jan 12, 2017
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I have dabbled in knifemaking mostly using old files and heat treating with rosebud torch with hit and miss success (on the heat treating part). I have always wanted a forge but either been to cheap or not had the time. The art department at the high school where I am a shop teacher just threw two large kilns in the dumpster. I used the forklift to get them out and salvaged most of the ceramic fiber bricks out of them. So, I have half a pallet of ceramic fiber bricks sitting behind my shop right now and I am thinking it is time to make a forge. I have been doing reading online and watching YouTube videos and I think I am more confused on what I want than when I started researching so I thought I would ask advice with some specific questions.

First of all, I am a shop teacher with access to a CNC plasma table, welders, and other metal working tools. At home I have a metal lathe as well and a 2,000 square foot shop so I am pretty capable in the fabrication area from both a skill level and equipment standpoint. I was thinking about making a steel rectangle tube to put the brick in. I have a bunch of 5/16 plate sitting around so I will probably use that though thickness should not really matter for the shell. I would like a ribbon burner but that seems a bit outside the time I have available right now so I would probably settle for two or three venturi burners which I would of course make myself. So...

1. Do I need to line the ceramic fiber blocks with a hard fire brick?

2. Do I need to use a mortar or can I just set them in tight together?

3. Do I need to coat them with anything? Some sources talk about putting some kind of coating on them to keep fibers from escaping.

4. Do I want the burners aiming straight down on the surface where the steel will be or angled a bit. It seems forges are made both ways.

5. How big should I make my fire box? I was thinking about having it be about 14" long but I am not sure about how wide and tall. I plan to make machetes and kukris so I do not want to go too small but I do not want to be too big either. I would have a removable back so I could pass stock all the way through if needed.

6. It seems a lot of the DIY forges are round... will my box type design get the job done?

7. Anything else I am not thinking of?

I have way too many projects I am working on such as a power hammer, a power hydraulic press, a pizza oven/outdoor kitchen, oilfield pipe fencing, and a gatling gun which is on the 10 year plan.
 
RANGER295 said:
I'm no expert, but I have built a small single burner forge. I'll answer your questions with what I believe to be the best answer, but other solutions may suit you better.

1. Do I need to line the ceramic fiber blocks with a hard fire brick? I use insulating fire brick. I don't know what kilns use, but I don't think it's the same. Maybe it is though. Insulating fire brick is not hard, and quite light compared to what is used to line fireplaces and is found at home centers.

2. Do I need to use a mortar or can I just set them in tight together? I don't think mortar is necessary or desirable. Dry fit will allow easy replacement when you discover damaged bricks that crack, or dissolve from using flux, or you decide to change your chamber dimensions.

3. Do I need to coat them with anything? Some sources talk about putting some kind of coating on them to keep fibers from escaping. Coating with an infrared refractory coating is completely optional and not at all a necessity. Applied properly to a well designed chamber it will increase forge efficiency, reduce fuel use, and might increase your max temperature to some degree. All of these things may be highly variable and dependent upon your chamber design. I use an IR refractory cement from Atlas.

4. Do I want the burners aiming straight down on the surface where the steel will be or angled a bit. It seems forges are made both ways. This may be argued the most. I'm not sure it will matter as much with a square chamber, but I agree entirely with the idea of a tangential burner placement in a round chamber and that's what I did. That achieves a vortex-like combustion and I believe that it aids in a more even distribution of heat in my forge. I have a single 30K Atlas burner and I can achieve over 2300F, but I also have a small chamber of approximately 3"x 9". A square chamber may not benefit from a tangential arrangement like a round chamber, but you are planning on 2 or 3 burners so I don't think it will matter much for you.

5. How big should I make my fire box? I was thinking about having it be about 14" long but I am not sure about how wide and tall. I plan to make machetes and kukris so I do not want to go too small but I do not want to be too big either. I would have a removable back so I could pass stock all the way through if needed. Size it for what you want to make. The more volume you have, the less efficient it will be and achieving and maintaining high temperatures will simply burn more propane. If you are only making blades, consider lower heights and widths. If you plan on making axe or 'hawks in the future or plan on other general blacksmithing you may benefit from a larger fire box. Like all things there is no free lunch, and many guys have more than one forge eventually to address that very fact. Construct accordingly.

6. It seems a lot of the DIY forges are round... will my box type design get the job done? It will. See my points above on some differences. round works well for small, efficient bladesmithing forges. As you get larger in diameter, the efficiencies of a round chamber drops, and square becomes more cost effective to build for the volume gained.

7. Anything else I am not thinking of? Burners are a big deal. Make or buy. If you make, be prepared for a possible adventure in tuning and getting temps to save a few bucks. If you buy from a well-known source that work has been done for you.

I have way too many projects I am working on such as a power hammer, a power hydraulic press, a pizza oven/outdoor kitchen, oilfield pipe fencing, and a gatling gun which is on the 10 year plan.
Click to expand...
Answers in red. As always, YMMV. Good luck!
 
There is a bunch of forge and burner info in the Stickys.

The brick you have is probably fine, but will need a lining that is resistant to the flames. A good layer of satanite or other refractory will do just fine. 1/2" is plenty. A coat of ITC-100 over the refractory is nice, but not a requirement.

You want a front port and a back port. If making them fixed size. 3X4 (HxW) is a good size front port and 2X3 good for the back. If making them adjustable make the port about 3" high and from side to side. Use firebricks to open and close the space as needed. Always leave some back port opening for the burner to run properly.

You can just stack the bricks and contain them in a metal box you make in your shop. No mortar will be needed. For the top bricks you can run 1/4" rods through them to hold in place.

The burner should be placed about 25% back from the front port and angled toward the rear at around 30°. Unless the forge is really large one burner will be enough.
The burner is what makes the forge run just like the engine is what makes a car run. Take the time to build or buy a suitable burner in size and ability. This isn't the place to save a few bucks going cheaper.

I prefer a blown burner, which is simpler to build and operate. You can even make the forge run at specific temperatures. Look at my PID controlled 2-stage burner plans in the stickys. If you build this, use a 3/4" ceramic TC sheath and a good 10 gauge TC.

Making a sliding work rest is very good idea. It is super simple to make when building the forge. I use two pieces of 1/2" tubing, one on each side at the height of the port, and two 3/8" solid rods sliding in them. Weld a 3" wide work rest across the two rods and you can pull it out or slide it right up to the port as needed. This is really useful for long pieces of stock or when the blade is in tongs. Make it so it can pull out at least 12".

There is lots more, but that is the basics. Use the Custo Search Engine to find the many forge build threads for ideas.
 
One thing that's not been mentioned - desired use of forge. For general blacksmithing work the square forge with burners directly down on work is popular. This allows the work piece to get to forging temps quickly heating only a small section. For knife work you want a round forge with burner mounted toward the front, angled back and upwards slightly. This allows a swirling flame that heats the inside of forge fairly evenly. In my round forge made from a 30# propane tank I can have a 12" billet that's a fairly even red or orange color from end to end. With the blacksmith type forge I had I would have had a small section of that 12" billet hot.

As Stacy says, a blown burner is MUCH easier to control for temp than a venturi burner. I've had venturi burners that worked good, but not nearly so easy to control temps as my current blown (forced air) burner. This type of forge helps a lot with preventing overheating billets.
 
Also, you can build a round forge with firebricks, Just bevel the sides and they fit together perfect. Use a piece of 12-14" pipe for the tubular shell or make one from sheet metal.
 
Thank you for all the replies. When I was on my phone I was having trouble finding the stickies. I will do a search specific to this site rather than a general google like I was doing. You guys have given me some food for thought.

Ken H> said:
One thing that's not been mentioned - desired use of forge. For general blacksmithing work the square forge with burners directly down on work is popular. This allows the work piece to get to forging temps quickly heating only a small section. For knife work you want a round forge with burner mounted toward the front, angled back and upwards slightly. This allows a swirling flame that heats the inside of forge fairly evenly. In my round forge made from a 30# propane tank I can have a 12" billet that's a fairly even red or orange color from end to end. With the blacksmith type forge I had I would have had a small section of that 12" billet hot.

As Stacy says, a blown burner is MUCH easier to control for temp than a venturi burner. I've had venturi burners that worked good, but not nearly so easy to control temps as my current blown (forced air) burner. This type of forge helps a lot with preventing overheating billets.
Click to expand...

As for the specific use... Bladesmithing not general blacksmithing. So far my knife making has mostly been grinding blanks such as files. I want to move up to actually forging from other stuff.

I was going to go with the venturi for construction simplicity but maybe I should use forced air.

Stacy E. Apelt - Bladesmith said:
Also, you can build a round forge with firebricks, Just bevel the sides and they fit together perfect. Use a piece of 12-14" pipe for the tubular shell or make one from sheet metal.
Click to expand...

I will have to find something larger than that or maybe just roll a tube. I do have a slip roll that will roll 14ga up to 12" wide and 16ga up to I think 18" wide??? would have to go back and look again. The refractory blocks I have are 4" thick so I have a bit to work with on shaping them.
 
The stickys are at the top of the Shop Talk page. The one named Metallurgical Discussion and Heat Treatment has what you want.:

Important Info! - Metallurgical Discussion and Heat Treatment Sticky - find Good HT info here

To comment on any thread linked in this sticky, just open the link and you will be on that thread. Larrin, Devin Thomas' son, is a metallurgist who freely gives his knowledge here. We greatly appreciate his deep theoretical info. It make my head hurt sometimes. His threads are linked below...
www.bladeforums.com www.bladeforums.com

There is a ton of good info in all the stickys. The custom search engine is also there.
 
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