We will start with a high-quality bellows like those by Bruguier, Frisard or Rochat. After checking the problem with the bellows, the first thing to do is to remove it completely and clean off the remaining adhesive. These bellows are very delicate, their valves are metal and they have a delicate steel spring to close off the air. In order to work properly, it is essential that the valves opens and closes perfectly. It is necessary to check the valve closure, as their operation is very delicate, and that the airflow meets no resistance when the valve actuates. In this case, two of the three air chambers, the chambers that blow in the air , measure 6 mm and the reserve chamber is 8 mm to 10 mm, depending on the model.
In this post I am going to explain how to reconstruct a bellows. Not all bellows are the same; depending on the period, the mechanisms can be very different.
To get the correct measurement for the chambers, I have built a jig and some separators with the right measurements, in order to put the leather in place with the right measurements. The leather is cut to the required size, folds are made in the leather if necessary and the proper adhesive applied to the edges of the bellows plates. After leaving it to dry, the process is repeated on the other sides. After closing in the bellows with the leather, the bellows must not be folded or forced. To make the holes for the air outlet and nuts I use a red hot needle. Now the bellows can be folded and the folds in the leather put in the right place.
The sound pipe and piston or modulator is screwed into the bellows. The pipe also has a valve that must be checked, as it produces the sound and the changes in pitch.
The bellows is then subjected to movement and checked to see that when the chambers move they blow air into the reserve chamber. When the modulator valve is closed, the reserve chamber inflates easily. Then all the components are assembled in order to check their operation and the song.
It is normal that after making the bellows, if the valves are not correctly adjusted, one can be faulty and even when the bird sings, the song is cut short and is not cheerful. Then it is necessary to open up the bellows again, check the valves, and redo it.
I use different types of leather. To cover the upper and lower plates and the modulator valve, I use a thicker, non-porous leather. For the bellows, I have various thicknesses. In this case, the normal thickness is like cigarette paper.. The leather needs to be treated before being applied. It must be washed and cream applied, to get a softer texture and not make annoying noises, since these calf skins tend to have a texture very much like paper. A high-quality fabric adhesive must be used to glue the leather to the metal, and to get the metal to adhere to the leather no ordinary glue or contact adhesive will do.
After mounting the bellows, it must be checked without connecting the mechanism completely, to see if the two chambers blow air and whether there are leaks. It must also be checked to ensure that the reserve chamber inflates easily when the bellows is moved by hand.