[HWooldridge]

Addendum: I posted this note in response to a question about lining a forge sometime in March 2005 but I'm not sure if it still resides in cyberspace. Glenn, you are welcome to post as a sticky or a blueprint, if one does not already exist with this information. I might also add I lined a forge with this clay recipe about three months ago (March 2008) and it is holding up fine with no cracks in the refractory - I hope it helps someone...



Lining a Forge:

I lined a Buffalo forge that has the lips an inch or so above the iron hearth and it turned out well. The process is based on something I learned years ago when I used to help my grandpa build houses. In addition to carpentry, he did some rock work and one thing we would do occasionally is reline fireplaces. On horizontal areas, he would make up a mix, apply it dry and level, then spray water on top. This would rock up in a day or so without cracking. The mix I used (based on his recipe) was 3 parts mortar, 3 parts clean sand, 1 part fireclay and 1 part dry lime. I mixed it, poured in the hearth to a depth that was flush to the top of the firepot and raked it smooth, then sprayed only enough water on it until the surface was wet. I let sit two days before making a fire and it had hardened nicely with no visible cracks anywhere. I think the minimal amount of water helps eliminate the cracking.

Coal Forges:

I have seen more badly constructed coal forges than good ones in my life. A lot of folks make their own (which is perfectly fine) without a basic knowledge of not only how but why it works.

All solid fuels need some amount of air pressure to burn properly. You can have too much velocity with insufficient pressure or too much pressure without enough air movement. The two extremes can be illustrated by a couple of examples. A light wind blowing on a campfire will make it hotter but only the outside of the fuel pile burns because the breeze can't make it to the interior. Conversely, hooking an air compressor to a firepot will make a fire but any amount of pressure much over a few pounds will blow the fuel out of the pot. The reason why bellows and centrifugal fans work so well on a forge is that they generate the right combination of both air supply and pressure. Too big a blower (like a large, electric squirrel cage) will lead to excess fuel consumption, more clinker and an oxidizing fire. In addition, a squirrel cage can be "stalled" because they are designed to move large amounts of air - not push it thru a mass of burning fuel. Conversely, too little air will never allow the fire to reach its proper potential for heating.

The proper size air inlet to the fire is also important. I'm sure a lot of folks have used grates drilled with a bunch of holes but 1-3 larger holes is better. One of the best homemade firepots I ever saw had a 1/2x3" slot cut in the bottom. The pot was entirely made from 1/2 inch steel plate and there was no clinker breaker. This arrangement made a nice hot fire with a center about the size of a grapefruit, which is about like a commercial pot.

I recently exchanged notes with a professional British smith who uses a side blast. It is simply a piece of 1" heavy wall stainless tubing as a tuyere and aimed slightly downward into a molded mortar "duck's nest". The coal is piled up in the hearth and forms it's own bed in the depression. Other fire shapes can be made by employing fire bricks to redirect the blast. This simple arrangement works well and eliminates all the Rube Goldberg creations that get built in back yards. The smith said he can easily weld with this design and some of these forges have lasted over 5 years in daily use.

I use a coal that generates a big clinker in a hurry but it was cheap, gets hot and cokes well so the only disadvantage is the dirt. Therefore, I have learned to build a fire and use it for a half hour or so then let the clinker cool for a couple of minutes. At this point, there is enough to usually pick up in one piece while I try not to disturb the coke around the pot. I can usually clean the fire and get back to work without breaking the whole fire down.

If I have one piece of advice about fire tending, it's that less is usually more. I have seen a lot of people that tear the whole fire down on every heat or spend the entire time digging up the coke ball. A fire has to form a natural bed to work properly and it takes a few minutes for this to occur. A good coal smith will replace the piece for the next heat and rake a little coke on top. As the fire burns hollow, the sides are pushed in a bit. This gentle management is done during every heat - you don't work for an hour and then tend the fire all at once.