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Questions about building my own forge


Dewm
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So i'm a complete beginner, although I have been doing a fair amount of research online... The type of forge I would like to build would be a bottom blown coal forge

 

 

And as far as building my own forge goes... what type of material should I line it with? clay is fairly limited up here and expensive..

 

Would a standard concrete work? like one of those premixed bags that you get from homedepot? or do I need something more rugged?

 

 

2nd of all, since we have winter 8 months out of the year, I need this to be indoors.. now I know about chimney venting etc.. my old house was heated with wood, but does anyone foresee any problems with putting the forge in my garage? its a 20'x23' garage with a 8ft ceiling, I don't actually use it for a garage.. its my shop now. But i've never burned coal.. if I have the chimney and draft set up properly should I expect any coal dust in the garage/shop? what are your thoughts?

 

Anyways thanks for any advice.

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As for materials, your best bet would be an old car brake drum or something like that. Concrete would crack under heat pretty quickly. Thick steel is really all you need. You'll need some sort of cover to vent the smoke out of the garage.

Trying to make each knife just a little better than the last

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Caleb is right, heavy steel plate with no insulation is what you need for that job. And yes, there will be coal dust and soot all over everthing in the shop if you use coal no matter how well vented. Just one of its more endearing characteristics...

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Thanks for the info, what thickness of steel would you recommend? I would prefer something a little more "permanent" then a break drum, although it gives me a place to start..

 

And along those lines. For the air venting in the bottom, should I worry about how thick the steel piping is? I'm not quite sure what temperatures I'll be reaching under the fire.

 

My current plan is to use standard 2" threaded steel pip to run from the forge blower to the output under the fire.. is that recommended?

 

Thanks!

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If you live near a city, check with the local authority for mass transit or construction company to see if they have some old break drums from large construction trucks or busses - they are darn near indestructible.

Once you can accept the universe as matter expanding into nothing that is something, wearing stripes with plaid comes easy.

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I would say that 1/4" plate should be the minimum thickness for your grate. I use 3/8" plate for my grate and it still gets warped after several hours of forging, especially at forge weld temps. I have melted 2 grates that were 1/4" plate. Keep in mind that coal puts out a lot of heavy smoke when it is green. So your stack need to be a good size in diameter (8" minimum) and fairly long to create enough draft to pull the smoke out of your shop.

Edited by mtodd
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Thanks for the information everyone! lotsa help

 

As far as the brake drums go, I live in a pretty small town.. But I might have to do some looking, it would save me time if I could find one off of a larger truck.

 

This is the firepot I had planned on building, and making the surrounding concrete.

 

flange.jpg

 

But after some discussion and looking through those pics on google, it seems like steel would be the way to go. So my next questions would be:

 

1. the surrounding area (I think is referred to as the "hearth"?) how hot does that get? and do I need more then 1/4" steel plate?

2. if I build the pot out of heavier steel (Like 3/4") how long do you think that will last? will I have to replace it often?... if ever?

3. what type of heat transfer am I looking at for the blower pipe? should I worry about how thick that is?

4. the hood, I had planned on a side draft. how hot will that get? I could imagine the heat loss out the top wouldn't be that great.. but I just don't know.

 

 

 

Little background: I am a certified structural, pipe, mig and tig welder. So while this is new....its not completely new :)

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With this design your heat will be centralized. Heat transfer or radiant heat will be somewhat limited. Concrete or cinder block filled with concrete and reinforced with rebar will easily withstand temperatures produced by a small firepot like this design. With this design I would think 3/8" plate will last a long time. If you plan on just making knives and nothing bigger like swords, this design will work fine.

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Thanks for the info again.

 

Yeah for now small hand tools and knifes are pretty much what I have in mind. If I feel like this is something I would like to do long term I might work on a larger setup, but my biggest restricting factor would be space. Maybe someday I will be blessed with a larger shop, until then...

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If you go for concrete, bear in mind it must be good and dry before you heat, damp and steam will form and chuncks of concrete flying about is not what you need! Scrap yards are a good place to look for brake drums, you can line it with 'fire place cement' ( that's what they call it in S Africa,) this will keep the outside of the drum cool and you too!( It's hard to work when the outside of your firepot is glowing red! Refractry cement is the best thing to prevent this happening and doesn't have to be thick...

To become old and wise... You first have to survive being young and foolish! ;) Ikisu.blogsot.com. Email; milesikisu@gmail.com mobile: +27784653651

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For the firepot, use a minimum of 3/8 " , 1/2 " is better and will last for years as long as it's hanging free in the air and you don't pour a bucket of water in it while it's hot. If you build it into solid masonry it'll burn out pretty fast no matter what, you need that air-cooling. The bottom of the pot doesn't get that hot, and the table (the part around the pot) doesn't get that hot either, the heat from coal goes mostly upwards. My forge has a cast iron pot hung in the middle of a 3/16" thick steel plate measuring 24" x 36" supported on a wooden frame. It gets hot enough underneath to cook the sap out of the pine 2x4 bracing, but not hot enough to char. It's lasted 15 years with zero issues, so I am not overly concerned.

 

The blower pipe (tuyere is the term) does not get hot. Air-cooled and all. Looking at the pot you pictured, I can say do not use that grate in the bottom. Coal eats gratings fast. Leave a 2 or three inch hole, and put a triangular ball on a rod in the hole so that there's about a 3/8" gap around the outside and the whole thing can be rotated to break up clinker and clogs. Google "clinker breaker " or "Tuyere ball" to see examples. Being the welder you are it shouldn't be a problem.

 

The side-draft hood won't get that hot either. I made mine out of 11-gauge sheet steel and it's lasted ten years with zero warpage. You won't want to lay your hand on it after an hour of forging, but it's not a fire hazard or anything.

 

Miles, if you're getting a brake drum hot enough to glow there's a problem in your airflow! Mine never gets nearly hot enough to glow.

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No Alan, I use a large fridge compressor tank, which has to be lined! But my wood stove does glow red ( where the missing hot water tank should be!) Great in winter...

To become old and wise... You first have to survive being young and foolish! ;) Ikisu.blogsot.com. Email; milesikisu@gmail.com mobile: +27784653651

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Ah, mystery solved! :lol: Yes, compressor tanks are too thin to use unlined. I was picturing a half-inch thick cast iron drum. And woodstoves can and do glow red quite a bit! My great uncle had a big old potbelly stove in his lumberyard business until the day it was glowing red and his son dumped a big scoop of green sawdust in atop the coals...

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For the firepot, use a minimum of 3/8 " , 1/2 " is better and will last for years as long as it's hanging free in the air and you don't pour a bucket of water in it while it's hot. If you build it into solid masonry it'll burn out pretty fast no matter what, you need that air-cooling. The bottom of the pot doesn't get that hot, and the table (the part around the pot) doesn't get that hot either, the heat from coal goes mostly upwards. My forge has a cast iron pot hung in the middle of a 3/16" thick steel plate measuring 24" x 36" supported on a wooden frame. It gets hot enough underneath to cook the sap out of the pine 2x4 bracing, but not hot enough to char. It's lasted 15 years with zero issues, so I am not overly concerned.

 

The blower pipe (tuyere is the term) does not get hot. Air-cooled and all. Looking at the pot you pictured, I can say do not use that grate in the bottom. Coal eats gratings fast. Leave a 2 or three inch hole, and put a triangular ball on a rod in the hole so that there's about a 3/8" gap around the outside and the whole thing can be rotated to break up clinker and clogs. Google "clinker breaker " or "Tuyere ball" to see examples. Being the welder you are it shouldn't be a problem.

 

The side-draft hood won't get that hot either. I made mine out of 11-gauge sheet steel and it's lasted ten years with zero warpage. You won't want to lay your hand on it after an hour of forging, but it's not a fire hazard or anything.

 

Miles, if you're getting a brake drum hot enough to glow there's a problem in your airflow! Mine never gets nearly hot enough to glow.

Alan if its not too much trouble would you mind sharing a picture of your forge? I have to rebuild mine soon and Yours sounds like a nice simple design.

Michael Cochran

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Sure! It's a commercial firepot from Centaur, http://www.centaurforge.com/Centaur-Vulcan-Firepot-with-Dumping-Ashgate/productinfo/VD/ , and the hood I made myself. The Stealth Fighter geometry is because I wanted a lot of volume, but only had a rather narrow space to fit it into. There's a 8" x 16" rectangular duct in the top connecting it to the chimney. It's important for a side-draft hood to have the outlet (including the chimney) a bit larger than the inlet to create a venturi effect, and if you've got a large volume between inlet and outlet it serves as a draft inducer.

 

Here's the forge (built 1999) with its brand-new hood and chimney in the freshly cleaned shop, 2004:

 

Aforge 1.jpg

 

Aforge 2.jpg

 

and here it is in 2006 with a little rust, and the shop slowly progressing towards its current mess:

 

Aforge 3.jpg

 

I apparently haven't taken any pictures from that angle since then, but it looks exactly the same today. Well, the forge and hood look the same, the shop is even messier... :rolleyes:

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