I have a fascination with bellows. We know they had to have existed in the Bronze Age, but unfortunately they are also constructed of ephemeral materials, so none have survived into modern times. The only physical evidence we have consists of fragments of tuyeres. An Egyptian painting from the Tomb of Rekhmire, from 1450 BC shows a man using pot bellows that are operated by hands and feet. There are also Chinese documents depicting the use of box bellows. But bellows, after blowpipes, are likely to be one of the earliest forms of delivering air to the furnace.
Until a set of bellows is uncovered preserved in a bog somewhere a lot is left to the imagination. How big or small could they be? How can the valves be altered to be more efficient? How heavy should the leather be? Should sturdiness trump suppleness? How are all the parts held together and made airtight? Bellows are one of the most essential pieces of equipment that we have for casting bronze and yet very little information is available about their use and construction from the community of experimental archaeologists and reenactment groups.
Over the years I’ve seen many different shapes and sizes of bellows and always thought that a forum where bellows design and use could be discussed would be invaluable for people to share ideas and experiences.
I would like to invite others to share photos of the bellows they’ve made on this site. This could be a welcome forum for discussing the pros and cons of different designs, what worked, what didn’t. Of course any news of archaeological bellows or tuyeres discovered would add to the fun.
To start, Martijn van Es sent me some photos of a set of bag bellows he made and photos of a new set he recently completed using the tutorial on this website. Martijn casts bronze at the Bronzezeithof Uelsen and Het Bronsvuur – The Bronze fire and is active on the web and Facebook discussing Bronze Age casting techniques and projects that he’s involved with.
Other bellows designs
I saw these pot bellows in use at Arbeia Roman Fort several years ago. They incorporate partially hollowed tree stumps and circular leather bags with the valve on top. This is one set of bellows that won’t shift around!
This has to be my favourite bellows idea. Simply made from two cement bags.
I welcome others to send in photos of their bellows, and not just bag bellows. Any bellows that could be considered to fit in with what we know or can surmise from archaeology would be interesting for this forum.
Tuyeres are the tubes that bring the air from the bellows to the furnace. They can be made of wood, ceramic, PVC pipes, copper pipes, really whatever you can come up with that will do the job. They are usually connected to the bellows, but in some cases they can just be set close enough that the air is delivered through them to the furnace. If you have a set of two bellows, the tuyeres are in a “Y” shape, with two ends connected to the bellows that connect to a single end going to the furnace.
Archaeologically there aren’t many remains of tuyeres. There are some fragments of tubular ceramic objects that had evidence of burning on the end. However, the best example is a wooden one recovered from a Danish bog. This was the same sort of “Y” shaped one described below.
Quick and easy: Tuyere #1
One of the problems of working with kids is that they are so fascinated with flames that they sometimes don’t realise that the bellows aren’t the part that supposed to be burning. So I’ve been working on making a couple of new sets of tuyeres.
I’m under a deadline for one set, so this one is a quick and easy version. I pulled a good sized forked branch from the woodpile and cut the ends so they were fairly even. Then I got a 22 mm spade bit (aka: a flat bit). Then I just clamped it into a vise and drilled into the flat ends of the wood until the holes met near the centre. I removed the bark, rounded off and sanded the ends. I don’t want any bark that will work loose over time, or any sharp edges that will abrade the leather.
These will be connected by leather tubes to the bellows and held in place by strips of rawhide. Skip down to the section on putting them all together for the details on that.
Note: Save that sawdust you’re generating with all that drilling. It will come in handy for making moulds!
Larger and more labour intensive: Tuyere #2
The next one is another wooden tuyere for a new set of bellows I’m making. It’s larger, so the spade bit isn’t an option. Instead I cut the wood in half lengthwise and then carved out the inside with a gouge. It’s all handwork, so it takes longer, but one advantage is that the diameter of the air holes isn’t limited to the size and length of the drill bit.
The first step was to trim the branches and strip off all the bark and then saw it in half. Once it was cut, I marked off where I would carve out the centre and went at it with chisels and gouges. I made the interior as smooth and as even as possible. However, I don’t smooth the surfaces that will be glued together. They already fit well and the rougher texture will help the glue bond.
Ceramic and other Tuyeres
If your tuyere might be placed close to the furnace (as mine accidentally was), it would be a good idea to make a ceramic extension. This is just a tube made of the same ceramic you used for making the furnace or moulds. It can be fit to the end of your wooden tuyere with leather and rawhide, as described below, and the end can go straight into the furnace. The only problem I find with ceramic tuyeres is the possibility of them breaking when being transported or if someone steps on them.
At the Terramare Village in Montale, the tuyeres they use there have a 90 degree bend. The tuyere sits on the edge of a small, shallow furnace and blows air straight down onto the charcoal. It’s an Early Bronze Age design and does get hot enough to melt bronze and copper. If you don’t have much space for a furnace this would be an ideal solution. It’s also worth experimenting with different types of furnaces and set-ups to get an idea of how many solutions there are to the basic question of how to melt and cast metal.
I’ve also made tuyeres using the stems of Japanese knotweed. The stems are hollow, similar to bamboo, but much softer. The plants can get over an inch in diameter and several feet tall. The stems can be easily cut with a knife, small garden shears, or secateurs, and then the membranes between sections can be broken using a straight stick. Note: Japanese knotweed is a controlled invasive species in Britain. Any fragment of stem, leaf, or root will take root and start a new plant. They are almost impossible to get rid of once started. When I find a large stand of knotweed, I strip off any leaves and excess stem and leave them there. If I need to trim off any more once I’m home, I put it in a plastic bag and then put it in the bin.
As I said earlier, tuyeres can be made of anything that will get the job done. If you don’t need to have that “authentic” Bronze Age look, you can quickly whip something together with PVC plumbing or copper piping. It wouldn’t be glamorous, but as long as any flammable or melt-able parts are kept away from the heat of the furnace, it should get the job done.
At the EAA in Glasgow, I saw a poster showing the reconstruction of a beautiful horse-headed ceramic tuyere by Katarina Botwid of Lund University. You can see the tuyere in action here.
Putting them all together
The tuyere still needs to be connected to the bellows. I usually make tubes of leather that fit the tubes coming out of the bellows and the ends of the tuyere.This allows for some flexibility and gives you a bit more distance from the furnace.
Then I tie them in place with wet rawhide. Once the rawhide is dry, they are about as secure as you can get. If the leather is soft, the tubes have a tendency to twist or collapse, so a nice solution is to get some green willow twigs and roll them into a spring. Fit them into the tubes before doing the final attachment and they’ll keep the leather tubes open and prevent them from twisting.
By the way, if you have a hard time finding rawhide lacing, buy a rawhide dog chew. Soak it in a bucket of water overnight and then cut it into long strips while it’s still damp. If you don’t need all of it right away, let it dry out. Then when you need it again just soak it for a few hours and it will be nice and flexible again.
This month (October 2015) I had the great adventure of doing some bronze casting with Il Tre de Spade (The Three of Swords) at the Archaeological Park and Open-Air Museum of the Terramare in Montale. The museum is located just south of Modena and recreates Bronze Age houses surrounded by a palisade and a marsh, appearing as it would have in the central and later phases of the Bronze Age there (1600-1250 BC). The museum hosts demonstrations and activities, along with a recreation of the original excavation.
The houses are nicely furnished, with well laid out areas for cooking, sleeping, food storage, and workshops. One house has a workbench for wood and antler working, along with weaving and other crafts. The other has a metalworking workbench with stone anvils, moulds, bellows, and all the needed kit stored neatly on shelves and a work bench. Unlike the recreated roundhouses that are often seen in the UK, you can get a good idea about how the ancient people lived here and where they put their all the things they used in every day life.
(Click on the thumbnails here to see a larger version)
I had been invited to join the casting demonstrations by Claude Cavazzuti, who is also part of EXARC. He is one of Il Tre di Spade (along with Pelle and Scacco) , who were some of the first metalworkers at the museum after it opened several years ago. They do regular demonstrations (sometimes with hundreds of visitors per day) and also run workshops that introduce people to Bronze Age casting and metalworking with a focus on the Middle and Recent Bronze Age (1700-1150 BC) of Northern Italy.
The furnaces there are small clay-lined trenches about 25 cm deep and 50 cm long, something that would be nearly invisible archaeologically and easily interpreted as a cooking hearth (and really, there’s no reason why they couldn’t be both). The furnaces heat up quickly and work efficiently. The charcoal is concentrated around the crucible with more warming beside it so that the fuel is hot before it gets raked around to cover the crucible.
My first new introduction was the bag bellows. They were larger than I have used in the past, and made of heavier leather. They put out an enormous volume of air, but also their size allows the person pumping the bellows to sit on a low stool. One nice innovation is that they put a large stone in the bottom of each bag. That prevents people who are new to bellowing from lifting them too high and causing the bags to collapse.
The real challenge for me was the valve and the way the bellows open at the top. The bag bellows I’d used before have straight sticks in the handles that either open parallel to each other, or are hinged at the back to open like a “V”. These bellows have two sticks on both sides, so that they open into a diamond shape with the wide part opening where your hands hold the bellows. It took a little bit to get used to them and to figure out where best to position my fingers. I never did get it quite tight enough and could feel a bit of air blasting on the back of my arms, but they still delivered a powerful amount of air. The tuyere was a large clay tube that curved downwards at a 90° angle, and was positioned so that it was directly above the crucible. This mean that the charcoal had to be moved frequently to keep the crucible covered. Without the layer of charcoal above, the air coming from the bellows would cool the metal in the crucible.
The crucibles are a flattened dish-shape, with some that were larger and a bit more of a bowl shape to hold more metal. They have a tab on one side that is used as a handle. The crucibles have a small lip for pouring that causes the metal to pour more quickly and flow out in an arc, rather than almost straight down like the triangular bag-shaped bellows used in Britain. It took a little bit of getting used to the trajectory of the metal in order to get all the metal in the pouring cups.
The tongs they use are beautifully crafted from wood and cord. They are kept in a bucket of water to keep them from burning when holding the heated crucible. The entire organisation of tools and materials is efficient and elegant, and there is nothing that would not have been found archaeologically from this period.
For the first demonstration a sword was cast into a sand mould. The sand they use is local, and perfect for casting. Commercial casting sand consists of fine sand and dry bentonite clay. The sand from the Po River delta is exactly that, sand that has been reduced to almost a powder by erosion, combined with clay and silt that has been washed into the river. The Po River sand leaves a much finer texture on the finished objects than the coarser commercial sand that I have used here. Looking at the quality of the sand, I could imagine how different sands might affect the regional quality of casting, and might even have had value as a commodity.
The mould for the sword was made using the standard cope and drag method, with the pouring cup on the side of the sword, rather than pouring from the top. A large vent was also placed at the tip of the sword. The mould was placed at an angle. As the crowd gathered and settled onto benches under a marquee, Claude explained Bronze Age metalworking techniques and then the sword was cast. Everyone was impressed and even more so when the sword was taken from the mould.
After the demonstration was done we started up a second furnace for the workshop. For this one we used the stone moulds that were on display in the house. The moulds were made of a very fine grained local stone, the same that had been used by the Terramare circa 3500 years ago. The moulds were warmed next to the furnace and then strapped together with leather strips. We took turns bellowing and pouring. The shallow crucibles mean that the pouring has to be done more quickly than with deeper crucibles. They cool quickly, so there is little time for dragging out charcoal and skimming. Once the metal was molten, we gave it a quick stir with a stick, pulled the crucible out with the wet tongs, and poured the bronze into the mould while holding the stick across the top to keep the charcoal back.
Sickles, knives, and daggers were cast. Later we moved on to using sand moulds. I borrowed one of the antler spindle whorls from the woodcarving house to see if I could try casting that as an experiment. It worked sort-of. It will take a bit of work to get finished up, but I think with a couple more tries we could have got it spot-on.
I was wearing my bronze torc bracelet that day and one of the new people wanted to try casting that. We used it as a model for a sand mould and after a couple tries, we got a cast that made a perfect duplicate.
While we were casting, more tour and school groups came through to watch more casting demonstrations. School kids also had the opportunity to make their own copper bracelets. There was a square of tables set up with small stone anvils and hammerstones. Punches and chisels were available so they could decorate the strips of copper to make bracelets in patterns that would not have looked out of place in a Terramare village.
Often after the casting is done for demonstrations the bronzes are taken home and finished up using drills and angle grinders, but not here. We had a relaxing time using wet sand on the hard, fine-grained anvil stones to grind off the flashing and excess metal. Some smaller stones that had a coarser texture could be held in the hand and used for working the inside curves and corners. I’d brought my small socketed hammer along and we used that to break off some of the metal, too. Between light hammering and patient grinding, the daggers were smoothed rather more quickly than I would have expected.
It was a great day, and one that was full of new experiences. It was particularly interesting to see how much variation there is in doing the same tasks and getting successful results. The different types of bellows and crucibles make for differences in how tasks are performed. Other small acts show variation between different metalworking groups. Tasks such as turning the crucible over to remove dross and leftover metal after casting was done into the furnace here, where in Ireland we have always done that next to the furnace. These are small things that could be seen archaeologically if excavation is done carefully, but also shows how customs and metalworking traditions develop with regional differences.
Next month I will be moving to Modena and will be in the vicinity of the park. I hope to do more casting there and to learn more about the Early Bronze Age metallurgy of Northern Italy.
A special thanks to Il Tre di Spade, Claude, Pelle, and Scacco and the staff at the Parco archaologico e Muse all’aperto della Terramare for inviting me to participate in casting. I would also like to acknowledge Markus Binggeli & Markus Binggeli who are masters of bronze casting and replicating ancient metalworking techniques. They are mentors of Il Tre di Spade, and provide both inspiration and technical expertise for experimental archaeologists.
If you’d like to learn more about the Early Bronze Age in the Modena area, the work of Il Tre di Spade, and the Terramare Open Air Museum in Montale you can find links below.
Italian language sites
English language sites
Il Tre di Spade also have a Facebook page.
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.
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.
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.
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.
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.
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”.
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.
These were made for a project in conjunction with Weston Park Museum in Sheffield. In the past I had used bag bellows, but we wanted something slightly more modern for an upcoming exhibit on the Roman presence in South Yorkshire. They were surprisingly easy to make and have held up well after many episodes of casting bronze and even an iron smelt
- Materials needed:
- Wood board
- Leather or vinyl
- 3 cm Copper coupling
- Wooden pegs
- Wood glue
- Linseed or other oil
- Wood screws
- Tacks (a box each of 25 mm/1” and 13 mm/ ½”)
- Upholstery hammer, or other hammer with a small face
- Linseed or walnut oil
- Contact cement
- Saw (preferably an electric jigsaw)
- Drill bit to match the wooden pegs
- 3 cm spade or flat bit
- Cord or clamps
A note about health and safety
I am going to assume that you are capable of safely using the tools and materials described in the tutorial. Don’t wear loose clothing when using power tools, or let long hair get in the way. Don’t use electric power tools outdoors in the rain. If adhesive has warning labels, pay attention to what it says. I’m writing this tutorial so that you will have enough information to make a set of bellows. As for everything else, you’re on your own and I would prefer you have a good time making and using a great set of bellows.
Designing the bellows
The first thing to do is to sketch out what you want the finished bellows to look like. Traditional fireplace bellows are teardrop shaped, but since I was making a set of bellows and would be sitting between them, I wanted them to have a narrower shape so I could easily reach both handles without having to rock my body back and forth more than was necessary. I also frequently work with kids and wanted the bellows to be manageable for them as well. This was also a consideration when designing the handles. You’ll be working with these for hours at a time, and so you want something you can hold easily without getting blisters or straining your wrists. Gripping the handles will just stiffen the muscles of your hands and wrists and wear you out. Design something that’s comfortable and enables you to shift or change your grip periodically. The handle I ended up with was one that I could easily lift just using two fingers and push down with the flat of my hand.
The eventual over-all design and size of the bellows was limited by the availability of places to buy boards of the needed thickness, by the size of board I was able to find, and the fact that I don’t have a car. Mega-hardware stores like B&Q in Britain don’t have proper boards. They have composite shelving, which if you look at it closely will have seams running the length of the board where two narrower boards were glued together. I worried that this would weaken and possibly break, so I had to find a place that had solid boards. I went to a small shop that does custom woodworking. It would have been nice to make them of oak, but all they had was 2 cm/ ¾ inch pine. I was extremely glad when the man there cut the board into lengths for me. It was a bit tricky since the board had knots and one large hole. We managed to figure out how to cut around the worst of them and I happily carried my supplies home.
Making the pattern
The next step was to make a pattern. I drew it out on newspaper, cut, taped, adjusted, and fiddled with it until I had it right. This really was the most time consuming part and rightly so. Take time to get the pattern perfect. Play with it. Pretend it’s finished and try pumping it. The time spent tweaking the pattern is time well spent.
Now, about the pattern. There are two large sections for the base and the top. The bottom piece would run the length of the bellows from the nose to the back. Rather than have two handles (like a fireplace bellows), the bottom would come just short of the handle (so I don’t knock my knuckles into the wood every time I pressed the bellows down. I did drill two holes in the bottom corners so that I could put tent pegs in to hold it down. My experience working with kids and plenty of adults) is that they tend to overcompensate and lift the bellows clear off the ground.
There are also two small pieces for the nose that will be laminated together with the bottom of the bellows. There are another two pieces that will serve to hold the leather hinge in place, and then the scraps that will be used for internal supports and feet. Just about every bit of the board was used in one way or another.
Once the pattern was made, I laid it out on the boards, working around knots and splits, so that it would be as solid as possible. I traced around it, and in one case changed it at the last minute, you’ll see some of the crossed out lines in photos of the interior. The important thing is to make any changes before cutting the wood.
The thing I worried about most was the valve. I searched, but nowhere could I find a formula for the size of the valve hole in proportion to the rest of the bellows. I looked at as many as I could and from what I could tell something about one third of the width of the bellows would be sound. The valve itself would be a thick, but fairly flexible piece of leather, so if the valve was too long it might have difficulty making a good seal. I remember one set of bellows that a friend from New Zealand had that were enormous, but had a problem with the valve. The valve was large enough that when drawn up the leather would flip backwards on itself. The bellows had to be flipped over and the leather pulled back down before work could continue. I fussed and fretted awhile, but knew that if I erred on making the valve hole too small, I could always enlarge it. I ended up with a valve hole 6 cm by 8 cm.
The other decision was if the valve would be on the top or bottom. For this I got some input from friends who told me that having the valve on the top was more in keeping with Viking/Scandinavian traditions and that in order to close the valve I would have to push down more forcefully. This is not as much of a problem if I was primarily using these for an iron forge, but casting bronze and smelting iron blooms goes on for hours. I need something that will be efficient and not require any extra effort. In addition, when I work with kids, I want them to be able to help with casting without having them concentrate solely on trying to get the bellows to work.
The disadvantage of having the valve on the bottom is that leaves and debris can get sucked in. I decided to put the valve on the bottom of the bellows and to put small risers underneath. Then I just have to make sure that where I set them up is free from debris. If I was worried about anything getting sucked in I could put a bit of wire mesh on the outside the valve. So far this hasn’t been a concern.
For convenience sake, I decided to make the tuyere (the pipe where the air exits the bellows) out of a 3 cm copper coupling. For this I needed a spade or flat wood drill bit of the same size.
Assembling the bellows
Now to the cutting. That was pretty much straightforward, and I found that the two pieces leftover from cutting the handle made a nice design when put back to back. I later glued them together and they became the shield shape of the hinge. Of course if you want to save time, you could just use a door hinge or some fancy looking strap hinges.
Long scraps were used for the risers on the bottom of the bellows. Miscellaneous pieces became the internal supports. These support the top of the bellows and prevent it from being pushed too far down and straining the hinge. Another support was placed at the back for the same reason. It also prevents the leather from being trapped and abraded.
Once everything was cut, it was fit together and small adjustments made. The next step was to sand everything. You want the wood to be smooth and comfortable to work with, but also to remove any sharp edges might scrape and wear holes in the leather.
Once everything is sanded and fitted, the final assembly can begin. The first thing is to glue and clamp the nose pieces together. I didn’t have enough clamps for the job, and also some of the pieces were awkward sizes, so I wrapped and tied cord around them and then twisted it with some steel chopsticks (A good sized nail would do the trick, too). Get the joins as tight as possible and then let them dry completely. Once they are good and solid, mark the centre and drill through the end using the spay bit. Fit the copper coupling in. It should be a tight fit. (Make diagram) Now from the inside widen the hole so that it is cone-shaped going back to the end of the coupling.
Meanwhile pieces of leather were cut for the valve. There is about a ½ – ¾ inch overlap on the end and sides and a bit more at the end where it is tacked in place. I doubled that part over to make a stronger hinge and used the shorter tacks to secure it.
I wanted to use wooden pegs as much as possible for the construction, but I realised that using some wood screws would make life easier. So the next step was to drill every piece that would need pegs and then to glue all the internal support pieces and secure them with wood screws. The internal supports were also cleverly lined up so the screws would help secure the risers. However, these were also drilled and pegged to the bottom of the bellows. Once again, everything was glued and clamped. Once it was dry I gave it a good coating of linseed oil. I used linseed because I had plenty on hand, but there are other good oils designed for woodworking.
Leathering the bellows
Now it’s time to go back to the drawing board. This time the design will be affected by how high you want to lift the bellows and your budget. Ideally this part should be made of soft leather, such as goat or pigskin. I’d love to have had the money for that, but had to opt for vinyl. Despite having used the cheaper material, it has held up amazingly well, and I do have the option of replacing it with leather on later. But whatever material you choose, a pattern must be made first. Bin liners / plastic trash bags are ideal for this.
Sit beside the bellows and lift the top up as comfortably as you want. Ideally you should be able to open the bellows to about 45° or a bit more. Think about your shoulders when you make this measurement. Measure the length from the handle to the bottom of the bellows and then add a few extra inches for rolling the edge under. Also remember you’ll be pumping up and down for hours. Also take into consideration that you don’t want the bellows to be so short that you lift them off the ground every time you pump them.
Now measure from the centre back around to the front. You’ll also need to have enough that both ends of the leather will overlap on the block where the tuyere comes in. The next dimension you need is the height of the front end. The leather should be a few inches higher than the block. Now a paper pattern can be made making sure that the sides and ends are symmetrical. Make sure to add an extra inch along the top and bottom to allow for folding the leather under when it is tacked in place. Get the pattern symmetrical by folding it in half lengthwise and adjusting it, and then fold it in half sideways and adjust that. Keep tweaking it until it’s exactly what you need. Use this to make a pattern from the plastic bags. This can be taped to the wood, and you’ll have an approximation of how the bellows will work. Try it out and make any adjustments before cutting into the leather.
Once it’s cut out, working from the centre back of the bottom, fold the leather so the cut edge is inside and secure it with tacks. I used the shorter tacks most of the way, but for some areas that get more stress, like along the corners, I used the longer tacks. Once you come to the front, pull the leather gently so that the edge is along the bottom, and tack it in place.
Put some tacks around the tuyere hole and cut the leather so there’s an opening. Do the same for the other side, overlapping the leather and cutting another hole. Put tacks in around the tuyere and the edge of the nose.
I had thought that I would need to glue the leather along the edges of the bellows, but I was pleased to find that the tacks did a good enough job and that there was no leakage.
Now for the top. Starting at the centre back again tack the leather along the edge, folding it like before. Overlap it along the front edge. There will be excess leather and you’ll have to push down a bit to get it to meet. At this point there will be a gap where the leather overlaps. Use some contact cement to seal the pieces together and let dry overnight. You’re almost there!
At this point you can test the bellows and feel how much air they put out. They work, but they’re a bit wobbly, so the final step is to make the hinge. You should have two drilled pieces of wood (if you didn’t drill them for pegs, wood screws will work well). One will fit closely over the top piece of the bellows and the other will go on top of the nose of the bellows. Push the top of the bellows down (it will take a little effort to cram the leather into place) and fit the top of the bellows so that it meets the edge of the nose.
Cut a piece of thick leather (the same type as used for the valve works fine) that will fit under both pieces of the upper hinge. If you’re using pegs, cut holes in the leather for them to go through. Glue the leather to the nose piece and to the wooden piece to go above the leather and secure them with pegs or screws, then do the same for the other half of the hinge. It should be a tight fit. The leather in the hinge will stretch over time, but after several months of use, I haven’t seen much change.
That’s it. You’re done. You’ve made a set of bellows suitable for bronze casting, forge work, or even iron bloom smelting. You can make them as big or as small as you want. Adjust them to fit your needs. Experiment and enjoy.
If you want to use one at a time, you can add a longer pipe (I’ve found old pipes from vacuum cleaners work well). However, if you want to link two of them together you’ll need a more elaborate tuyere. There will be more on tuyeres in another article.
Here is another bellows making website: