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Making bag bellows

Bag bellows might be the oldest form of bellows used. We don’t know for certain because they are made entirely of organic materials, and so none survive in the archaeological record. They are still used for iron forging in parts of Africa and South Asia. Plus they have the advantage of being portable, lightweight, and easy to make. You can be as “authentic” as you want, using only wood and leather, or you can use more readily scrounged materials like vacuum cleaner hoses and cement bags. There is a remarkable video of Kenyan metalsmiths using bellows made of cement bags here.

Traditionally bag bellows are made of soft leather and the usual description is that a single bellow is made from one goatskin. The bellows below are made with upholstery fabric. At the time I made them, leather was too much for my budget. I do find it ironic that in the Bronze Age leather would have been readily available, but hand-woven fabric would have been exorbitant. So, these are my ostentatious display of wealth bellows. They are sealed with a good coating of linseed oil that made them both waterproof and airtight and have worked well for many years now.

 

My very posh bag bellows
My very posh bag bellows

 

Designing the bellows

How big the bellows you make will depend on what’s comfortable for you. I’ve used very large bellows and ones so small you’d think that they’d never produce enough air to get the job done, but they did remarkably well. What is important is that the size works for you. You’ll be sitting on the ground, or close to the ground (I like a padded log or a short tree stump myself). Sit down on the floor and raise your arm a little over waist high. You’ll be pumping your arms up and down for hours, so it’s good to find a height that is comfortable for you so that you don’t wear your arms out. Measure that height or get a good idea of how high that is. You’ll want to add a few more inches because you will want to have the bellows rest on the ground. If you lift them too high, the sides will collapse and you won’t be able to trap the air in them. You also want to add another few inches at the top to wrap around the handles.

The other supplies you’ll need are rawhide, heavy waxed thread, leather or sail needles (depending on the type of material you’re sewing). The handles are made of two straight branches about 3-4 cm (1-1 ½ inches) in diameter, or four boards 3 by 0.5 cm (1 by ¼ inch) by whatever length you decide upon for the width of your bellows. If you use branches, they’ll have to be split lengthwise so that they have a semi-circular cross section. My bellows are about 38 cm (16 inches) wide by 63 cm (25 inches) high.

Using your own measurements, adapt the pattern below, adding about an inch for the seams around the edges, and extra at the top to wrap around the handles.

bellows pattern better

 

You’ll also want loops for your fingers. The loops are more important than you realise. Getting them right will mean the difference between being able to work for hours, and giving up because you keep getting blisters or losing your grip. If you used branches, you might not need loops for your fingers, but I find that they make the bellows far easier to use. The loops are simple, just strips of the same material that your bellows are made from. They should accommodate four fingers on one side and your thumb on the other. Sew them so your hand will be about 1/3 to ¼ of the way from the back of the bellows. Having the loops toward the back means that you don’t have to open your hands as wide. Since I work with kids a lot, this was a consideration when I designed them. Also, I have small hands. The loops will stretch over time, so I periodically have to stitch them again to tighten them up.

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Another useful detail is to sew a small triangle in the front of the bellows, just below the handles. When the bellows open, the little triangle in front will allow the bellows to open in a “V” shape and allow you to trap more air. Holger Lönze taught me this trick. It makes it much easier to open the bellows and get more air in.

The triangular piece in the front. Note that I have stitched it so that the triangle folds inwards so that when I close the bellows it is trapped inside.
The triangular piece in the front. Note that I have stitched it so that the triangle folds inwards so that when I close the bellows it is trapped inside.

 

Another detail to work on is the part at the bottom that sticks out. This is where the tuyere will fit. The size you make that will depend on the tuyere you make, and also how much air you want to push through to the fire. If it’s too little, you’ll be expending a lot of energy pushing air through a small space. Too large and you’ll be pumping furiously to get the volume of air through the tuyere. Mine is about 10 cm (4 inches) and tapers a little so I can fit different tuyeres to it in case I ever want to change it.

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The other supply you’ll need is rawhide. Leather can work, but it isn’t as durable or tight as rawhide. The best source for rawhide I’ve found is the pet shop. Buy a rawhide chew bone for a dog and soak it in a bucket of water overnight. The rawhide will soften and you can untie the ends and unroll a nice sheet of rawhide. I cut it in a spiral while it is still wet so I have long pieces. While it’s wet, you can manipulate it easily. Once it’s dry it shrinks to a hard, tight fit.

Now to assemble the bellows

Cut out the leather or material and then stitch it with the outsides together so that when you turn it inside out, the raw edges will be on the inside. Don’t sew it all the way to the top. You want that extra selvedge to wrap around the handles. Make sure you fit the triangle in the front below the bottom edge of where the handles will be.

The next step was the hardest for me. It’s a bit of a pain. You need to wrap the upper selvedge of the bellows around the sticks and sew them tightly into place. If you’re using half-round branches, make sure the flat sides are on the inside so they meet and make a tight fit. It’s annoying if they wobble around. Sew these in tight along the bottom of the sticks, and then sew the tops together at the back of the bellows so that when you open them, they form a “V”.

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The handles stitched in place. Note how tightly they are sewn at the bottom of the handles

 

 

Turn the bellows right side out and admire your work.

There now, try them out. Try pumping them a bit and see if you can open and close them easily. When the bellows open, the little triangle in front will allow the bellows to open in a “V” shape and allow you to trap more air. The action is to open them while the top of the bellows is close to the ground, Lift them, close them when they are as high as you want to lift them, close the bellows and push down. If you lose your grip, you might want to tighten the loops.

If you feel any air leaks in the seams you can seal them with linseed oil. If you made your bellows from fabric, the easiest way to coat them is to hang them on a clothes line outside and slather the oil on with a paintbrush. It takes a long time to dry and smells pretty strong. It’s definitely something to be done outdoors. Keep in mind that it might take a day or two for the linseed oil to dry.

Now in order to use the bellows, you’ll need at least a short tuyere. If you’re not fussed, a hose or steel tubing from a vacuum cleaner work fine. If you want a more Bronze Age look, you can make them from clay or wood. I took a short branch about 4 cm  (3 inches) in diameter and drilled a hole in it using a 2 cm flat bit (1 ½ inch spade bit in the US). If you don’t have a bit or don’t want to use power tools, take a branch of the right thickness  and split it in half. Carve out the centre and fit them back together.

Fit one end of your tuyere into the opening at the bottom of your bellows. Now take the wet, sloppy rawhide and wrap it tightly around the part of the bellows covering the tuyere, making sure to tie the ends off tightly. If your tuyere is made of split branches, keep wrapping so that it holds the halves of the branch together. Depending on the weather and humidity, it might take several hours for the rawhide to dry.

Once everything is dry, try them out. They’ll be a bit stiff at first and will need to be broken in. It takes a bit of practice to get the Open-Lift-Close-Push rhythm going, especially if you do it alternately with both hands. Once you get into it, it gets easier. Think of a cat kneading its paws. If it helps, rock slightly from side to side.

Another tip is to get some thin willow twigs, about the size used for making baskets. Make them into hoops that will fit inside the bag of your bellows. It will help keep them open, especially if you have a tendency to lift them too high.

Keep in mind that none of this is set in stone. These tutorials are meant to be basic, and are based on the things I’ve done. Experiment. Try different sizes and shapes. Feel free to add bits or change things. Adapt them to yourself. If you want to share your experience with bag bellow making, make a comment to the post here.

 Modifications: Well, you can never have too many bellows, and every time I make a new set, I add in some improvements, or I at least experiment with new ideas. The latest addition is twig rings to keep the leather from collapsing. One of the hazards is that the leather tubes leading from the bellows to the tuyere can collapse or get twisted. One solution is making a spring out of willow, but that can dry out and break after awhile. Another solution is to make a ring that is inserted into the leather tube at the bottom front of the bellows. I took some slender twigs (willow or hazel is ideal, but in this case I used cottonwood) and twisted them into a circle. Then I wrapped them in sinew (string will do too). They can then be inserted into the opening and either glued or sewn into place.

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Woven twig ring inserted into the opening of the bellows. This will keep the leather from collapsing or twisting and keeping the airflow steady.

 

 

 

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