clamshell forge

I've seen a "clamshell forge" which has 2 slightly hollowed disks of metal filled with castable refractory. The bottom one is fixed and has a wide lip,
and the top one can be raised with a long lever, and has propane burners in it. The smith in whose shop I saw this uses such a forge for doing larger flat objects like 10x10" steel plates. I see vague references on the Web to Ron Reil having a "clamshell forge" but no pix.
Anyway, the other day I was eyeing a Weber kettle someone was throwing away, and I thought "hmmm". Anyone else thought of making a clamshell forge out of the shell of a Weber barbecue kettle?
Grant Erwin Kirkland, Washington
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The depth of the Weber kettle and lid are far too deep to make a decent clam-shell forge. I have been collecting various clam-shell designs for a long time and in my opinion some of them offer the most versatility of any design out there. Ralph Sproule became interested in the design from me, and he went after it in his typical all out and well thought out fashion. The result was a series of very fine designs, complete with a "burner traps" to prevent any chimney action when the forge is shut down. At this time I probably have 10 or more designs in my files, and will be building a design of my own where I take the various features that I like from each one and combine them into my "perfect" design, perfect for me that is. I need a forge with an 18" x 24" chamber floor area, and that will allow the work to stick out from any side, and only the clam-shell can do that. Ralph's are based on a solid refractory tile floor, with bricks being piled up into whatever wall height, shape, and diameter is required. The top is mounted on a camper jack that can be cranked down to close it. I want mine to be easily height adjustable, but also have a foot treadle to lift the top for quick placement and removal of the work.
I am in the middle of a very intense Master's degree in technology program that has prevented me form having any free time to forge for the last 11 months, but I have only 11 months left and I will once again be pounding iron and will build the forge at that time. I have several decorative gates I need to make, and the clam-shell will make that work easy. Also, I am in the process of getting my big 8" x 8" bending post done to allow me to easily bend heavy sections. The post fits into an 18" deep floor socket. It is removable when not needed. I still need to make a heavy steel cap for the post, and drill holes in it for the bending posts to fit in various arrangements as needed. The bending post is kind of the other half of my clam-shell project. The post is mounted in its floor socket in front of me as I am typing this, but still needs the top plate, paint, and handles for removing the post from the floor socket. Hopefully I will have both items done in a year or so. I will post images of them when they are completed for anyone who may be interested.
Ron
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On Thu, 04 Dec 2003 08:12:18 -0800, Grant Erwin

Weber barbecues are too thin to make barbecues.
How about propane gas cylinder ends ? -- Die Gotterspammerung - Junkmail of the Gods
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Well, the shell wouldn't take that much heat, not if the refractory was thick enough ..
Grant
Andy Dingley wrote:

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On Wed, 10 Dec 2003 10:54:26 -0800, Grant Erwin

I'm thinking about rust. Heat / rain cycling (which is what they're going to get round here) will be through them in no time.
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wrote:

I make bowls shallow or deep using 3/16 or 1/4 plate cold using a hydraulic press. I originaly made them as feed bowls for my goats but I have thought of using these bowls for such a forge.
I would be willing to share the technique if anyone is interested.
Is there a burner in the top and the bottom ? How do the traps work to prevent the chimney effect. Are the burners tangent to the bowl or do they point strait up and down ?
brad
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This will be short as I have been in class all day and still have to go out to the Nutcracker with my family tonight..
The trap is done by having the burner mounted on top of the forge, but aimed up slightly from the horizontal. It is attached to a 90+ degree elbow that directs the flame down into the forge. That way when you shut down the hot gasses will not travel up the burner. Works great. I will post an image to my site soon and post the link here.
I would be very interested in how you make the bowls. I have a big fly-press so could most likely do it with that too.
Yours,
Ron
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I will try to get a digital camera over the holidays and post a step by step guide. I got the idea while building a large cyclone for a grain distributions system. Part of the cyclone consists of a large cone approx 12 ft in dia and 20 ft high. It was 1/4 plate which was large than the capacity of the rolls. So we used a press break to "bump" the profile of the cone.
To form a bowl I used a piece of maple stump pressed into a section of 12 in dia pipe. This forms the bottom die (the die does not last forever and must be changed eventualy).
The top die is 3 in dia ball bearing attached to the end of the hydraulic ram.
The process is similar to raising a bowl with a hammer except a concave form is used. Starting on the rim of the disk begin pressing slight impressions into the disk while continously rotating the disk. On completion of each revolution move to closer to the centre. Many gental "bumps" work better than a few aggressive "bumps"
As wrinkes form in the rim the ball bearing die is replaced by a flat die to press the wrinkles flat.
Continue this process until the desired bowl is created.
I have created bowls from 4 in to 36 in in diameter up to 1/4 in thick. With a little practice a bowl can be made in a few minutes.
There some pictures of some mushrooms that I forge using this process. The caps of the mushrooms are from 6 to 12 in in dia and all are 3/16 in thick. http://www.centipedeforge.com/products.htm
The winkles in the caps are deliberate and they can be made perfectly smooth.
I have a 50 ton press with a foot peddle which makes the process rather easy. I also have a fly press ... not as big as yours but I could try it and report back with my results.
ttuls brad
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Great description, much appreciated. I don't think I would want 1/4" for my clamshell top, most likely 3/16" or 1/8". So it would be well within the range of my fly-press, although the throat is limited in the press. That will not matter however because it could just as well have a flat center area. It would be 18" x 24", and my throat depth is 6-1/2", so it would theoretically have a flat section 5" wide by 11" long in the center. That would work out fine. Actually I may not use a bowl shape at all but just a gentle curve. Two of the clam-shell designs I have are done that way, and are really excellent designs. One of them uses the Kaowool in a series of "deep" folds right up against each other, with the support studs in the bottoms of the folds so they don't get hot...much like some of the pottery kilns are done. That design would take a lot of Kaowool, but the insulation factor would be superb. It will be a fun project when I can get to it. I would be very interested in seeing your images when you can get some. I do that kind of forming by hand in my Repousse work all the time, (when I can get time to work metal) but that is thin silver, steel, brass, or other metals, not 1/4".
Well, I am about ready to crash after my 20 hours of class this weekend and last, so I will close, and close up the shop, and head inside. Christmas break starts on Friday, so I may finally get a chance to decompress a little and play with some hot iron. :-)
Yours,
Ron
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