Depth of coal forge

Greetings!
I'm in the process of building a coal forge built around a large brake drum. I fired the forge a while back with charcoal
(
http://nika.frontier.iarc.uaf.edu/~cswingle/tmp/forge.jpg ), and the thing is clearly too deep.
Right now I'm building up the middle of it with the Pearlie and furnace cement refractory mixture, and wondered how high I should build it in the middle. Is there an appropriate slope from the rim to the center that I should be shooting for?
I was also thinking about using a 3" pipe cap with 1/4" holes drilled in it as the thing in the middle with holes in it that allows air in, and keeps the coal from falling down into the trap (tuyere / clinker?). Cheap, and easily replaceable. It's not clear to me what makes a good vs. bad clinker and would appreciate some advice.
Thoughts? I'm a traditional woodworker looking to make some simple tools (chisels, knives) as well as doing some heat treating.
Thanks!
Chris
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Christopher S. Swingley wrote:

The tuyere is the air nozzle. My guess is that the cap would stick up into the firepot in an unpleasant way, but I've never tried it. Maybe a plug would be better?
Clinker is the melted ash & dirt that sometimes accumulates in the firepot. Good clinker is in somebody else's fire. Bad clinker is in your own.
- ken
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On Fri, 12 Dec 2003, Ken Rose wrote:

Even clinker has its good side. It's just like they told us back in the Seventies--blacksmithing is a key craft for self-sufficiency. You can make your own gravel!
Conrad Hodson
who has a path out to his forge that isn't muddy any more
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You don't want anything sticking up into the fire. I use a portable forge for demonstrating that has a 6" round piece of 1/4" plate over the hole. It has about 8 or 10 1/4" diameter holes drilled in the central part and is bolted to the bottom of the forge with a couple of 1/4-20 bolts with nuts on the other side. This is so that, as the plate burns out, I can simply unscrew or cut off the bolts and make another plate. But, I use a 5" deep firepot at home and it has a clinker breaker in it. This is far superior to plate with holes. A clinker breaker is usually a triangular piece of steel or cast iron that rides on a shaft that goes through the tuyre from front to back just below the top surface of the bottom of the firepot. There is a crank on the shaft so you can rotate the triangular clinker breaker. The size of the clinker breaker is somewhat smaller than the size of the hole, so there is plenty of room for air to blow in around it, yet the area of the triangle is enough to keep hot coke and coal from going through. As far as I know, a deeper firepot is always better. If I ever see one that is too deep, I'll let you know. Even though my "home" fireport is 5" deep, I have surrounded it with a layer of 2" fire brick to make it effectively even deeper.
As far as "good clinker": A good clinker is a missing clinker. All it does is to take up room in the firepot that should be filled with glowing coke.
Pete Stanaitis -------------------- Christopher S. Swingley wrote:

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Ahhh!. I see the issue.
When you build the fire, you will build it so is is as deep as the firepot, so when you put work into the fire, you put it on top of the fire, about level with the top of the firepot, not down into it. Then to keep the heat from radiating away off of the work, you put some pieces of yesterday's coke on top of the work. This reflects the heat back at the piece, and adds a lot of efficiency to the job.
In your case of annealing a "long piece of car spring", you will need to gently heat one section to a medium red, then move to work so that the heated section sticks out of the fire a little ways while heating another portion. You will move the part back and forth every 20 or 40 seconds to even out the heat. Depending on the steel in that spring, you will have to cool it slowly or cool it very very very very slowly to get it to soften.
Maybe you should consider finding a way to get access to a chop saw?
Pete Stanaitis

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Excellent tips, thanks!

Probably should have said "car leaf spring" since I could have meant a coil spring. I also have one of those, but I have a feeling a flat piece of steel will be easier to work with to start.

I've got loads of ash from my wood stove, so I probably would just pack ash around the heated zone until it cools, then cut it with a hacksaw.
Another idea might be to heat the section I want to cut and then use a triangle file or the triangular-shaped end of my sledgehammer to cut it while it's hot.

That would certainly be ideal, I suppose. But the general issue of putting a longer piece of steel in a brake drum forge would still remain. Maybe I shouldn't be worried about this so much, since I'm starting out with what is an inferior forge as it is. But I figured I'd get as close as possible to the optimal with what I've got, and upgrade later. Building up the floor of the drum with furnace cement and pearlite gives me a lot of flexibility.
Thanks!
Chris
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<< There's nothing which says the grate plate has to be round. Just use a square or rectangular piece of steel plate if that's what you have handy. >>
Why not use a round or square cast iron floor drain? They are relativly inexpensive and can be found at most building supply stores (Home Depot, Lowes, or even your local Hardware store) The holes are close to a quarter inch and as it comes in two parts, (base and drain lid, it seems like it would work for a air supply and allow you to take the plate out between sessions to clean out the clinker.
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Thanks. Both posts are spot on -- I'll probably just head over to the Borg (big orange box) and see what sorts of cheap, replaceable chunks of steel with holes predrilled I can find. My initial thought was to use a "tin" can, and just punch holes in the bottom -- one can per fire. But I'll bet I'd burn right through it in the first heat of the forge.
Chris
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