The Coffee-Can Forge
Copyright © 2004
(Click images to enlarge)
Burning hydrocarbon fuels like propane, natural gas, and MAPP raises several serious health and safety hazards. Burns, fire, and carbon monoxide poisoning are among them. There are probably others I haven't thought of. Be sure your workspace is clean, controlled and well ventilated. It is best to work outside. If you burn fuels indoors, such as in a garage or shed, be sure to provide adequate ventilation and be sure to use a carbon monoxide alarm such as those available from Kidde. Be careful!
A frequently occurring problem in the home shop is the need to heat a small workpiece. Perhaps a steel rod must be bent to a tight radius. Maybe an old tool needs to be re-hardened, or maybe you want to heat-treat your own chisels or plane irons.
A common propane torch is often put to the task, but it can't heat any but the smallest parts evenly, or to an appreciable temperature. The main problem is that when the torch is used alone, the vast majority of its heat is too quickly lost to the surrounding air. This small forge helps by efficiently containing the heat generated by the burner.
The coffee-can forge certainly doesn't approach the capability or durability of a serious forge, but it works plenty well for occasional use. Its simplicity keeps the cost low and the construction well within the reach of the average do-it-yourselfer. The small size and low cost of operation make a coffee-can forge useful even in better-equipped shops. Mine gets nearly as much use as my mini propane-tank forge, which runs a Reil propane burner. That one is modeled on Ron Reil's freon-tank forge.
|The most expensive component is the burner -- a "swirly" propane/MAPP torch. This one is a BernzOmatic TS4000T, available at the Borg* or local hardware store.|
*Borg = Home Depot, Lowes, or whatever huge chain is taking over your area.
This torch has a handy trigger start and puts out considerably more heat than a basic pencil-flame jet torch. The downside is cost. Expect to spend around $40US. On the upside, you'll probably never want to use your old pencil-flame torch again after you've tried one of these in its place, even for quick jobs like sweating copper pipe joints.
The remaining materials are:
Any tin of adequate size will do, but even with the insulation, it will get quite hot, so an unpainted can is best. This one is an old cashew container. The steel strip is available at the Borg or hardware store.
Try a brickyard or pottery supply to find the firebrick. This is the lightweight stuff. It is simply what I had available, and it does work well enough for occasional use. It's more like foam than brick. It cuts easily with a hacksaw blade. It also breaks easily and generally tends to fall apart over time, as evidenced by my supply of irregular shapes. Ask your brickyard or pottery supply if they have any broken bricks or damaged kiln liner pieces for cheap. The heavier firebrick is more durable, and you might consider getting some of that if your crowbar is in better working order than mine.
The unusual item in this "kit" is the ceramic blanket. There are a few manufacturers. Kaowool and Durablanket are the biggest brand names. A higher temperature rating is better. You want at least 2300F, in the 1-inch thickness and 6-pound-per-cubic-foot density. Unfortunately, it can be hard to find small quantities of this stuff without paying outrageous prices. Here are a couple good sources:
(see also http://www.lametalsmiths.org/news/JayHayes.htm)
(You will have to email him.)
(This site requires a Java plug in to see the prices. You can get the 1", 6# material for about $3.50 per square foot, in 2-sq ft increments.)
Mine came from McGills Warehouse, a discount supplier of high temperature products. They have excellent prices on knock-off materials, but high minimum order quantities. The smallest quantity of ceramic wool you can buy from them is a two by twenty-four foot roll. The price is insanely low, but it is offset by shipping. Unless you have a need for the additional material, you're probably better off ordering from one of the two suppliers above.
|The coffee can is cradled in a pair of legs bent from mild steel strip. It is lined with 1" 6# ceramic wool blanket.|
The torch nozzle fits into a 3/4" hole cut into the side of the can, about midway between the open ends. If you drill the hole, clamp the can to a piece of wood that is securely attached to something heavy, and drill through the can into the wood. Otherwise, you'll get a nasty surprise when the bit grabs the can as it breaks through. If you have a 3/4" hole punch, that'll do even better.
Trim the ceramic blanket to size and line the can. Wear gloves and long sleeves. A respirator is another good idea. This stuff is not unlike insulation. Extend the can's hole through the liner. A sharp pocket knife works well for this.
A one-inch thin slice of soft firebrick provides the floor. It is slightly more durable than the wool. A ceramic shelf would be better, but I don't have any. Put the floor in so that when it's level, the hole ends up at about the 10 o'clock position.
The torch rests on a 2-3/4" tall block of wood with the nozzle poking into the hole less than an inch. It doesn't protrude past the lining into the forge cavity. The trigger guard is flat so the torch stays in place if I don't bump it. (G) A simple holder would be nice to cradle the torch and tank so they can't be knocked over so easily. I need to get a round TUIT.
A tuft of ceramic blanket covers the top half of the back opening. The front opening is usually closed off a bit by a firebrick or two sitting on the hearth, which is just a firebrick resting on its side in front of the opening.
You can't see it in any of these photos, but there's also a firebrick laying flat on the bench, butted up against the back of the forge. Resting on it, a few inches behind the back opening where it doesn't restrict the exhaust flow, is another firebrick on its side. If you look carefully through the lit forge in the enlarged image, you can make out the second one. The exhaust gasses blowing out the forge openings are searingly hot, and without this protection, the wooden bench where the forge is perched, and possibly the wall behind it, would soon be charred, at least. It would be better, of course, to locate the forge well away from anything flammable and dispense with the need for this precaution, but the point is that common sense is your best friend. Be consciously aware of the hazards involved in what you are doing and take steps to avoid an unpleasant experience.
|The atmosphere in the forge is controlled by choking the front and back openings more or less with scrap firebrick.|
An easy way to limit oxidation of the workpiece is to choke off the forge openings a bit. This creates a fuel-rich (slightly reducing) atmosphere inside the forge. Much of the excess fuel is burned at the forge openings. However, the amount of unburned and incompletely burned hydrocarbons is increased, and so the quantity of carbon monoxide produced will be significantly greater. Heed the warnings at the top of this page.
I generally close off the back a little more than the front, except when I want to limit the portion of the workpiece that's brought to temperature. That way I can estimate the atmosphere by the amount of flame at the front opening.
To make it easier to heat longer stock, a stand can be fashioned from another piece of steel strip.
To make the forge more efficient and durable, apply a coat of ITC-100 HT to the interior surfaces. ITC-100 is one of the thermal coatings produced by International Technical Ceramics. It is highly IR-reflective, so heat is retained within the chamber better. This reduces fuel consumption, since the workpiece will reach working heat sooner. The coating also helps protect the ceramic blanket and limits airborne dust from it.
A pint of ITC-100 costs $30-$40 depending on where you buy it, and covers 6-12 square feet. A gallon can cover 50-100sf. My propane-tank mini-forge, which is coated with ITC-100, has about 2 square feet of interior surface area. The coffee-can forge has 0.5 square feet. Jay Hayes has a good price on the ITC-100. I found some at a local ceramic supply shop for $33, which isn't too bad when shipping is considered.
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