My summer project this year was building a Japanese style box bellows, and since I am now about as done I as I can be without testing it on a real fire, it is time to show off a bit!
A bit of background: The box bellows are the Asian equivalent of the traditional double bellows used in Europe. In the US, they are mostly associated with Japanese swordsmiths - I took the basic design for mine out of a book on Japanese swords - but they were actually invented in China about a thousand years ago and have spread all over that end of the Pacific rim for all kinds of metalwork. They are pretty simple - a box and piston with a set of intake and exhaust valves at each end. As the piston is pushed and pulled, the intake and exhaust valves open and close alternately, the exhaust valves emptying into a secondary air chamber, often referred to as the "birdhouse" and from there into the tuyere.
Over the last six years or so I have been trying to put together a small blacksmithing outfit, without much success up until now. I don't have money to buy stuff and I am in a rather unsettled period of my life in which building a large, permanent forge is not practical now nor seems likely to be in the near future. Lately I have been looking more and more at the very minimalist equipment used by early medieval smiths in Europe and pre-Industrial Revolution cultures elsewhere. I decided on the box bellows because 1) it can be worked with one hand, necessary for a one-man operation, 2) I am a better woodworker than leatherworker, 3) it is a bit more compact than a traditional European double-lung bellows, and 4) because it can be placed on the ground and used, in a pinch, with a hole dug in the ground for a forge or a lined box placed on the ground, unlike a double lung bellows which has be used with a built-up forge. If I do get a more elaborate forge sometime in the future I can make legs for the box bellows. I am planning to use charcoal for fuel; I don't know if it will work well for coal.
Now on to pictures! Here is a photo showing the bare box. You can see the two intake valves at the top, the small hole 3/5th of the way down is the hole for the push-rod:
Another shot of the bare box showing the exhaust valves near the bottom:
Here are the valve flaps. All four are identical, made from masonite backed with cloth from an old pair of pants.
Here a couple shots with the piston and valves installed.
Inside:
Exhaust valve:
Birdhouse built:
The hole in the side is where the pipe to the forge will go. The piece of molding helps seal the joint there, since there are no screws from the inside to pull the top piece tight against the body.
And finished!
The material is mostly 3/4" cabinet-grade plywood. I put the nice side inside the box, as I wanted to have as the inside of the box as smooth as I could, to minimize air leakage. The push-rod and handle are made from poplar - probably not the most durable choice, but I was on a budget and had some 4' sticks of poplar that I could plane down nice and straight. At the moment it doesn't have any sort of gasket around the piston or the hole for the push-rod - traditionally they do, but mine seems to work pretty well without it. I will probably add some in the future, to increase efficiency. The finish is two coats of polyurethane, not very traditional but heat and scratch resistant.
The main box is about 36" long, 13" wide, and 21- 1/2" externally, and about 34" x 11 -1/2" x 20" internally, with a useable stroke of about 29-1/2", though I think I will probably only use about 24" of that stroke most of the time. 36" inches is about as short as you want to get - I have found that since my arm seldom pushes directly in line with the handle, the rod tends to bind a bit when the piston is drawn completely back. A longer box would help with this.
Total cost was about $30.00 for the plywood and about $8.00 for the screws, plus the use of some scrap to build the birdhouse and some leftover cans of polyurethane that my parents have had for 12+ years and where happy to see go.
