Making Bellows the Easy Way

by Melvyn Wright

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Making Bellows the Easy Way
When I made my first bellows by following the John Smith video, it took me a week and ended up being a total disaster!  Glue everywhere, stiffeners all over the place, and the glue had dried before I had even finished trying to line everything up. I vowed to find a better method - One that worked!

Since then, I have made around 15 sets of bellows, either for organs or for my various experiments and 'inventions', and I have developed lots of easy tricks to simplify the job.  I used to hate making bellows, now I quite enjoy it!  This is a collection of all these hints and tips:

   
If using blackout material for the bellows, make sure that it is airtight.  I bought some expensive 3-pass blackout cloth from ebay and, although it was light-tight, I found that I could blow straight through it!  So don't think that the expensive stuff is the best.

MDF is perfect for the bellows boards - preferably 1/2" (12mm) thick.  Seal it with diluted PVA glue.  Drill holes halfway through with a flat bit, from one side then the other.

When cutting the cardboard stiffeners, allow a gap of 1mm between the edges of the cardboard and the boards, top and bottom.  This is to allow the sides to fold inwards without being restricted.  There is no need to leave a gap between the upper and lower stiffeners because the cloth folds in the opposite direction along the centre line, which moves the stiffeners further apart.  In fact, the lack of a gap down the centre will help prevent the cloth from blowing outwards.

Cut away the corners of the front stiffeners very slightly where they butt against the side stiffeners, to allow the cloth to fold 90 degrees around the front of the boards.

I use duck/duct tape for the internal bellows hinge.  It's much easier, stronger, and sticks instantly.  But beware that PVA glue won't stick to duck/duct tape, so use cloth or leather for the outside hinge.  Don't mess about trying to fold the internal hinge in half, position the two bellows boards together and stick the tape straight across the joint.  Use a strip of 3mm thick MDF to act as a spacer between the two boards when they are closed.  To be honest, I am not convinced that the internal hinge actually does anything!

 

Cutting out the leather
You will need to buy a complete animal skin to cover the bellows.  This will be a completely random size and shape, and will probably be much  too big to fit on your table.  You will undoubtedly need to reduce this into a more convenient size before you can work on it, and it's difficult to know where to start.  What I do is to cut it into long strips to make it more manageable.  Start by cutting a straight edge along the top of the leather, removing the irregular edge.  This gives you a reference to work from.  This seems very wasteful, but you can probably use this spare leather for making the valves, as long as it's nice and flat.

Now cut the leather into strips which will be the width to suit the open bellows.  For instance if you want your bellows to open 3", the width of each strip will be just over 5" (3+" plus 1" for the thickness of the boards, plus 1" overlap).  It is likely that you will need 6 of these strips, unless your leather is so big that it will stretch all the way around the bellows boards.  Two of these strips are glued together end-to-end to make 3 very long strips that will go around each of the 3 bellows.  The length of each strip should be equal to the length of the bellows boards, plus the width of the bellows boards, plus 2" for the overlaps.  When glued together they should be long enough to go around the bellows boards, allowing for a 2" overlap at the hinge and at the front.  Before glueing the strips together, make sure to roughen up the smooth side of the leather with sandpaper.

When finished, draw a centre line along each of the 3 strips.

 

Double-Height Stiffeners
I recently tried this trick to simplify the task of making, cutting, and glueing on all the cardbooard stiffeners. This is a fiddly job at best, and accurate placement of all 6 pieces is not so easy.

Instead of 6 separate bits of cardboard, I made just 3 double-height ones and scored them down the middle. This eliminates half of the marking and cutting out work, makes it much easier to position them accurately, strengthens the central fold, and prevents them from lifting off the cloth. Quite a lot of advantages for doing half the work!

These bellows ended up very slightly stiffer than the normal method (as you would expect) but the difference is negligible, and doesn't affect their operation at all. I would guess that the score will eventualy separate after prolonged use, but that won't matter. The idea is to simplify construction.

If you are using thick leather for the bellows, this idea probably wouldn't work so well because the leather would try to pull the 2 halves apart at the score line.  The result would be a stiffer central fold.  I have tried it with leather up to 0.8mm thick and it works fine.


The three stiffeners, cut out and scored, ready to fit

 
Measuring and Cutting the Stiffeners

The middle stiffener should be equal to the width of the bellows, and the height of the bellows minus 2mm. The cut-outs are not exactly 45 degrees (although 45 degrees works).  They should be cut away slightly more, to make more room for the sides to fold in.
The side stiffeners should be the same height as the front stiffener, and taper down to a point where the two boards meet at the hinge.  The 1mm clearance at top and bottom is produced automatically by the MDF spacer between the boards at the hinge.  You could cut out one stiffener and then draw around it to mark out the others, but I prefer to measure each one out individually, as it is more accurate.  Draw a line down the centre of all the stiffeners and score along the line. Fold the stiffeners in half and flatten out again.  Before glueing on the stiffeners, you need to cut the point off the side stiffeners (around 2" from the point) and trim the 4 points off the middle stiffener.


Cut the stiffeners out with a sharp knife, then snip the points off

 
Marking Out the Cloth/Leather (Don't bother!)
I now save a large chunk of time by not marking out the bellows cloth at all. I just draw a centre line. After you've cut out the stiffeners, they can be lined up on the centre line and glued on, without any other markings on the cloth.  Then cut the cloth around the stiffeners, leaving about 3/4" margin all around.  This method is particularly useful for leather, as the leather easily pulls and stretches out of shape during marking and cutting, so the marks end up being mostly meaningless!

Apply glue to the 'valley' side of the stiffeners  with a brush, and carefully place them on the cloth, lining each one up with the centre line drawn on the cloth.  Start with the middle stiffener, followed by the side ones. For extra accuracy, check that the distance between the two side stiffeners is exactly equal to the width of the bellows.

Wipe any surplus glue off, so that it will not ooze out onto the cardboard stiffeners. When dry, trim around the cloth, remembering to leave about 3/4" margin to glue the cloth onto the boards.


The stiffeners glued onto the bellows cloth, each one aligned with the centre line.  No other marks are needed.

 

Glueing on the Bellows Cloth/Leather
I found that the method of glueing on the bellows cloth by holding the bellows vertically in a vice (as shown in the JS video) and starting from the front was very fiddly and inaccurate.  Accurate placement is rather hit and miss because you are working from the outside and can't easily see the position of the cardboard stiffeners in relation to the edges of the boards.  It's also slow, the glue gets in places it shouldn't, and the glue has started to go off by the time you get to apply any clamps. As if that wasn't bad enough the bellows are closed so the cloth keeps trying to pull itself away from the boards and come unstuck.  A complete disaster!

I found it was very much faster, easier and more accurate to do it the following way, (and you don't get glue all over your fingers neither!).  PVA glue is alright for glueing leather, but not so good for glueing blackout cloth.  I use Copydex to glue blackout cloth.

Before starting, it is best to make sure that the front cardboard stiffeners are exactly the same width as the bellows boards, and make the two small cuts in the front corners of the cloth that allow it to fold outwards along the top board (see John's video if you don't know what this means).  It doesn't matter if the front cardboard is not exactly the right width, as long as you take this into consideration when positioning the cloth on the boards in the following procedure.

Method
Lay the bellows cloth flat on the bench.  Apply glue along one long edge of the bellows (both boards).  Apply it quickly with a brush and wipe away any that runs down between the boards.  Place the glued edge carefully on the cloth, lining up the cardboard exactly between the two bellows boards (remember the 1mm gap).  Check that the corners are in the correct position.  Press down hard for a minute to press the boards firmly onto the cloth/leather.

Now apply glue to the front edges and also along the upper edges of the boards.  Put plenty of glue in the corners.  Fold the cloth up the front edges and check that the cardboard is sitting in the correct position.  Finally, fold the cloth over the top edges and line the cardboard up with the hinge end of the boards.  Pull the cloth tight and press it well into position all around, then place a heavy book or clamps on it and leave it overnight (or preferably use the edging strips described below).

This method is very fast.  I did a pair of bellows and a reservoir in under 5 minutes, with no fiddling about at all.  The weights or clamps can be applied very quickly, leading to a stronger joint.

It might seem more logical to start with the front of the bellows first and then glue the sides; but I have found that method to be much more fiddly as the bellows keeps wanting to close up, and the front edges don't lie flat on the bench.  Try both methods and decide for yourself.

Note that the bellows remains fully open throughout the entire operation, there is no need to close them or crease the cloth, as it tends to unstick the glue.

When dry, trim the ends of the cloth, fold them over the bellows hinge and stick down.  This should be done with the bellows closed. (Don't forget to roughen up the surface before glueing onto the smooth side of leather.)

Leave for at least 24 hours for the glue to fully cure before testing the bellows or putting any pressure on them.


 


Bellows placed on cloth and accurately positioned against the cardboard stiffeners. Note the 1mm gap


Glue applied to the board edges


Wrap the cloth around the board in one go and pull it tight.  Making sure that the cardboard stiffeners are centrally placed. This  method only takes a few seconds!


Completed bellows. The spare cloth is trimmed off around the edges when the glue has dried

 


If using blackout cloth, instead of trimming it off, it is a good idea to fold it over the edges and glue it down onto the boards.  Especially on the corners, where leaks are more likely to occur

 

Rather than use weights or clamps, it is preferable to pin strips of wood or MDF down the sides of the bellows to hold the cloth or leather firmly in place. Use veneer or panel pins. This is a good idea anyway, as it prevents the stiffeners from trying to force the cloth off during use.  If you are going to do this, it is a good idea to do it whilst the glue is still wet, and prepare the strips with the pins in beforehand.  Check that the cloth/leather is pressed onto the boards all the way round and add extra pins if not.

To make your bellows more flexible, close them, clamp them up tight, and leave them for a day.  This presses the folds and sets them.  You may be surprised at the difference this makes.

Simple Spill Valve

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