Read the project introduction here.
David Gingery's "Charcoal Foundry" calls for a steel 5 gallon bucket to be used as the basic shell for the foundry. The book was written in 1981 (?) and since that time, the use of metal buckets seems to have faded to a minimum, out-competed by poly buckets.
I bought 5 gallons of roof repair asphaltum in a metal bucket, but I don't think I'll ever use it all, and don't think I could get the bucket clean if I did. Thompson's Water Seal comes in a metal bucket, but costs nearly $50 for 5 gallons.
Other folks have improvised solutions to the dearth of metal 5 gallon buckets.
A popular solution seems to be the flimsy popcorn tins seen around holiday time. Others have used cheap imported stainless stock pots.
I ran across a solution in an interesting place, as a result of a sometime hobby, homebrewing. The homebrew supply place I go to sells malt extract by the pound, dispensing it from large metal barrels with spigots screwed into them. I asked the owner what happened to the barrels when they're empty and he said "Do you want some?!" He was happy to be rid of them, since I was taking away his garbage for him.
Here's a picture of one of the barrels, to give you an idea of the size. The print on the side says 80Kg, so this is roughly a 20 gallon barrel.
[Calculation: 80 Kg * 1 liter / Kg (water) * ~1 quart / 1 liter * 1 gallon / 4 quarts = ~20 gallons]
I've included a plastic 5 gallon bucket in the picture so you can get an idea of the size. I think the bottom 2/3 of the barrel compares pretty well to the size of Gingery's 5 gallon bucket, so that's what I'll use for the body of my foundry furnace.
You will also notice a can of WD-40 in the image. One of my gripes about photographs on the Internet is a lack of scale. I intend to include this regular-size can of WD-40 as a scale reference in most of my pictures. Where this is impractical, I'll try to include some other ubiquitous object for scale.
NOTE: you should not judge scale by the size of my hands in the images, as I have enormous hands. I am 6'4" (193cm) tall, and am not a small man. My wedding ring is large enough to admit a US 25 cent piece (a Quarter).
So, a 5 gallon plastic bucket stands about 15.5 inches tall, so we'll round that to a nice 16 inches for the barrel. Add 1/2 inch for a seam, so we can roll the metal and have a nice smooth edge:
I marked the barrel with a chalkline, then with a piece of soapstone. I center-punched just "North" of the line so I could drill a pilot hole, then cut around the line.
Notice my Peltor hearing protectors. Not only do they get used at the range; I use them in my shop on a regular basis. I've damaged my hearing enough already (mostly hunting quail as a kid, with a 20 guage and no hearing protectors. Take my advice... wear them even when you're hunting. It all adds up) Jigsawing a metal barrel ranks right up there with jet engines and heavy metal bands, so I wore the hearing protectors. If I had the electronic kind with the volume control, I'd probably forget I was wearing them.
If you're contemplating buying a jigsaw, don't bother with this Black & Decker low-end model. It is complete crap. The foot plate is attached to the plastic case of the saw with one screw. It wobbles and is nearly useless for anything other than rough work. I bought this one because I was in a bind, and had a gift certificate for a very overpriced hardware store in a chichi neigborhood. I would have saved up for a better tool, but this is what I have. I had picked up a couple of metal-cutting blades for it in preparation for this project.
Here's a look inside the barrel
This barrel has been sitting in my workshop for months, but the caps were in place, so the malt extract was probably usable until I contaminated it with metal shavings. I love the smell, and now my shop is going to smell like malt for a while. I wonder if it will smell like malt when I fire up the furnace :D
I sprayed down the dried malt syrup, and hung the barrel on a metal post to drain. I expect a big sticky pile on the ground when I get home. After most of it drains, I will hit it with some nice hot water and it should come clean easily.
What comes next:
I'm going to fold the rim of the cut barrel inward, probably around a heavy wire to make a nice beaded edge.
I'll cut some tubing to form three legs, which will be screwed onto the barrel.
2 holes get cut in the barrel, one for the "emergency" spill at the bottom, in case a crucible breaks, and one for the tuyere (pronounced "tweer"), which is where the air blast would enter the furnace, if this were going to be fueled with charcoal. It could still be used with charcoal, but I intend to use a propane burner instead.
A section of the lid of the barrel is going to become the lid of the furnace too. It has a nice rigid seam at the top and a pair of wire handles, so it should be easily converted to a lid.
Drop me a line to let me know what you think: Rick AT Mnemodyne DOT com (This way confuses spambots. Type it the usual way in your email.)
Until next time,
~Rick
04.05.2002
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Cutting Torch: April 6th, 2002
My dad brought me a torch to play with. It's a journeyman size oxy/acetylene rig. It had plenty of acetylene, but the oh-two bottle was dry. My neighbor Mr. Gomez told me about a good place to get welding gasses, GOS or Garland Oxygen Supply. I got the small bottle swapped for a full one for $13.00. Mr. Gomez is a retired aerospace machinist. He gave me that metal workbench you see in the photos. I imagine I'm going to be bugging him a lot :D.
This evening, before I had to leave for work, I fired it up and took some test cuts in some 1/4" scrap steel I had scavenged. It felt good to melt metal and make sparks. I cut a clean "bite" out of the corner of the test piece, and then was able to heat up a nice molten puddle and move it around, so I think I'm going to be able to weld smaller stuff if I don't get too ambitious. No photos, though... I was having too much fun playing with fire!
Man! it has been a long time since I did any torch work or welding. I'm surprised I was able to get the flame adjusted so easily the first go. I guess when they say "it's like riding a bicycle; you never forget how" they were right. I look forward to a lot of burning holes in stuff and melting stuff together in the near future.
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Here there be Dragons!: April 18th, 2002
It has been a while since I posted, mainly because I've been having too much fun playing in the workshop or playing with my baby daughter to want to write web code.
It feels like I have accomplished a lot since I started, so let's catch up....
Last time, I had cut the barrel in two pieces. Here I'm bending down the top 1/2 inch, to make a smooth edge.
I wish I had measured more carefully, so I could have made the top a lot more even, but I will even it out with the refractory.
Next, I cut up a piece of galvanized conduit (about 1.5 inch diameter) that I had scrounged from somewhere. There was enough to make three legs, each 12 inches long. Three legs is always stable, even if the ground is not level. It is important to have the barrel raised above the ground, because in the event of a crucible breakage or spill, you don't want the metal to cool and harden inside the furnace. We'll talk about the safety hole a bit later.
I attached the legs from the inside with self-tapping sheet metal screws. I initially used three screws per leg, but decided that wasn't sturdy enough, and added two more each, for a total of five per leg. The legs are canted slightly inward because of the angle of the barrel, but it seems sturdy enough. I may add some bracing later if it seems necessary.
I cut the top off the top section of the barrel, to a depth of about 2.5 inches (inside). This will form the removable lid for the furnace. I'm not sure if the wire handles are going to be sturdy enough; I may need to rivet on heavy-duty eyes for a 1/4 inch round stock handle, or something similar.
I cut a hole 2.5 inches in diameter for the vent, and smoothed the rough edge a bit by hammering it flat.
I cut a piece of sheet metal flashing to size and rolled it to fit the hole in the lid. This will form the vent hole when the refractory is tamped into the lid. The screws are semi-temporary. None of the galvanized metal should be heated above the vaporization temperature of zinc, which is considered somewhat toxic to inhale. I've been told that the antidote for zinc vapor exposure is calcium, so drink a glass of milk or take some Tums and you'll be fine.
I cut 0.5 inch tabs on one end, then folded half of them out, then fit the form into the hole and . . .
folded down the other tabs on the outside of the lid. I ended up trimming the inside tabs quite a bit so I will be able to remove the form more easily. I also reversed the screw, so it screws out from the inside, and trimmed it down nearly flush, so it won't dig out a lot of the refractory as I remove the form. Again, I have to get rid of the zinc before I fire the lid. [Update: Zinc's not that toxic]
Next I drilled eight pairs of holes around the edge of the lid, and threaded wire through in a star pattern. This wire acts as a support to keep the refractory from cracking and falling out. I'm thinking of bending in the edges slightly, perhaps at a 45 degree angle to further help support the refractory ceramic in position.
Here I'm cutting the safety hole in the bottom of the barrel with aircraft shears. I drilled a 1/4 inch starter hole, and nibbled my way around the circle. The dimensions of the safety hole aren't critical, but I chose 2.5 inches for this dimension too.
Here you can see the safety hole form in place in the bottom of the barrel. It's made nearly the same way as the lid's vent hole form. It will be removed while the walls are packed with refractory, then installed so the bottom of the form can be filled. Not show are the two or three half-cylinder forms I'll imbed in the refractory to form "channels" so that any spilled metal can flow under the plinth and down the safety hole.
The next major component is the cylinder form for the barrel. This form regulates the thickness of the refractory wall as it is tamped into place in the barrel. The barrel is approximately 15.5 inches deep, measured from the inside.
I cut two 9 inch diameter discs of 3/4 inch plywood, using my RotoZip tool and circle attachment. The RotoZip is pretty cool, but you have to let the machine cut at it's own pace. Forcing it results in broken bits.
The disc on the left has a handle shape cut into it, to make it easier to remove later. I sanded the edges with the discs stacked, so there wouldn't be any eggregious differences between them, then sawed a 1 inch kerf into the edge with my hacksaw.
Hooking my tape measure into the cut and pulling it tight around the circumference gave me a measurment of right at 28 inches. I added 2 inches for the lip and overlap, and cut a piece of sheet metal 30 inches by 15.5 inches. I folded up a one inch lip, inserted this lip in the hacksaw kerf of the discs, then rolled it up into a cylinder.
a little gaffer-tape (left over from my cinematography and stagehand work) and it's all assembled and ready to go.
The green pipe is to form the burner entry port in the side of the furnace. A hole will need to be located and cut in the side of the barrel. Inconveniently, the hole falls right on the barrel's reinforcing rib, but it's not an insurmountable difficulty.
The curved cut in the end of the burner port form is produced by a technique called parallel line development, and is really pretty cool. I may make a page explaining it, but it's pretty well covered in David Gingery's book Building a Gas Fired Crucible Furnace, from which some of my furnace's design is derived (though the one described in his book is -much- bigger and nicer).
At the same time as all of the above work on the furnace patterns was going on, I was also acquiring the parts and fittings required to build the burner.
This burner design is based on the work of Ron Reil and others, as outlined on Ron's burner pages. It is a venturi-effect burner, which means that no external forced-air system is needed. The venturi-effect is a suction created at the air intake when the jet of propane shoots down the burner tube. It's basically a big Bunsen burner, just like in chem lab.
The first part of the design is the fuel supply. Here, a 0-60psi adjustable regulator equipped with a 0-60psi guage is attached to one of my 20lb. propane cylinders, and to a ten foot high-pressure propane hose. I may end up buying an 80 or 100 pound cylinder.
The non-adjustable regulator from a barbecue grill will NOT work. Don't bother.
This regulator cost over thirty dollars, and so did the hose. The guage cost about five. This was a pretty big expense, but I figured I'd need a good regulator no matter how many burners I end up building, and a good quality hose should last a long time. It only hurt for a little while. Besides, getting the high-pressure regulator means I can really crank up the heat when I want to : o )
Here are the major parts of the burner. That's a 3/4 inch pipe nipple, a 0.75 x 1.5 x 1.5 inch reducing tee, a 1.5 inch cap, a 1/8 inch by 6 inch pipe nipple, a 1/8 x 1/4 inch bushing, and a 1/4 inch ball-valve, rated for gas.
Also in the picture, in the plastic case, is a set of "propane orifice drillbits" from Drill Bit City. Instead of using these to drill a hole for the fuel jet, I used a Tweco 14T mig welder orifice tip, from a welding supply store. These cost about $ 1.50, and are made from copper.
I forged the end of the 1/8 inch pipe nipple down until it was smaller than the 1/4 inch Tweco tip, then threaded the nipple so I could just screw in the Tweco tip.
This leaked, but worked long enough to test the burner. I have since brazed the tip on.
The 1/8 inch nipple is inserted through a hole in the end cap, and the 1/8 by 1/4 bushing is brazed onto the end cap, so that the 1/8 nipple can be unscrewed from the "inside" of the endcap if it needs to be replaced or adjusted.
Eventually, a metal disc will form an air-supply choke over the air intake, mounted on a threaded rod brazed inside the air intake opening. This will allow the amount of air to be regulated, adjusting the flame from "oxidizing" to "reducing", along with "rich" to "lean" fuel adjustments.
I'll try to get a non-blurry closeup to post next time, since that should make it clear.
With these components assembled as shown, I lit my propane plumbing torch as a "safety match", and fired up the burner. When I lit the propane through the air intake, the burner would gutter and blow itself out at anything but the lowest supply pressure.
When I lit the end of the burner, it would burn fitfully and go out. If I left the plumber's torch aimed at the end of the burner, it would burn fairly well, but go out if the plumber's torch was removed.
Here's a couple images of the burner test in darkness. Cool flame, but you can see the plumber's torch flame keeping it going. Something wasn't right.
The answer was the last piece of the burner design, the flare.
The flare is a conical metal shield applied to the end of the burner. This cone is tapered at the rate of 1:12, or one inch for every twelve. The flare is made from fairly heavy stainless steel food-service sheet metal I found at Phoenix Metal Salvage, in McKinney, TX. I cut out a pattern based on Lionel Oliver's template, and rolled it up into a cone, applying my ball-peen liberaly. When I finally got the shape and tension-fit I was looking for, I stuck the flare on the end of the burner and fired it up. . . .
The difference was dramatic! With the flare in place, the flame is even and consistent, and doesn't blow itself out, even at full throttle; 60psi of propane delivery!
I couldn't wait for night-time to take these shots to post here. I had a lot of fun playing with the burner until my wife said "Okay, it works: stop wasting fuel."
"Awwwwwww! But...!" So I packed it in and went inside. ; o )
The flare is only needed when you're running the burner outside the furnace. The furnace acts like a big flare, containing the flame and keeping it stable, so when the burner is heating the furnace, the flare can be removed or retracted.
What's next:
Now that I have the forms essentially finished, I need to mix up the refractory and let it "mature" for a day or so before I ram it into the molds.
I calculated the approximate volume which needs to be filled with refractory at about eight and a half gallons.
The mixture I've decided on is as follows:
Four gallons of dry silica sand
Two gallons of "mullite", which is a substitue for "grog"
Three gallons of dry fireclay
Three quarts of borax.
That comes to approximately nine gallons, dry, so it should be about the same wet, since we won't add much water at all for a nice stiff mixture.
I'll also make a few plinths (crucible supports), then any excess can be stored in an airtight container and used for patching later.
Since my ratio is pretty simple, if I run short of the refractory, I can mix up some more, or just leave the lid for a second batch.
The plan is to cover the rammed-in refractory with a damp cloth to prevent the surface from drying too quickly, then let it cure up a bit until it's hard enough that I can remove the forms without the refractory slumping.
Once I can remove the forms, I can fire the lining immediately. I have the burner basically finished, and as long as I make sure there's plenty of propane on hand, I should be ready to fire the lining of the furnace and lid at the same time.
I also ordered a crucible and some aluminum flux, in preparation for having the furnace done. I haven't taken pictures of the crucible yet, but I'll document that when I build the crucible tongs and other foundry tools I need from the 3/4 x 3/16 hot rolled steel I bought the other day.
It's been fun getting this far, and I feel like I've gotten further faster than I ever expected... especially after so much planning and dreaming and preparation. I hope to be more dilligent in bringing you timely updates from now on, but I won't make any promises.... It's easy to get carried away out in the workshop. For now, have fun and don't burn yourself (much). Too much and "it don't grow back." ~Rick
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