A bellows is an odd thing to find nowadays, though still a useful one. It's essentially two wooden handles and a leather sealed chamber in which air can be blown out. They were commonly used to stoke fires and forges hundreds of years ago. You might find one in an antique shop or old stately home, but it will probably not be in working condition.
Begin by designing your bellows. Lay out a piece of newspaper and draw the outline, from a top-down view, with your marker. There are three basic parts of a bellows: the handle at the rear, the chamber at the centre which should be wider than the handle, and the head where the nozzle is. The head should be flat and at least two inches wide at the front. All together the outline is up to you to design, just make sure the very front and rear are flat, the bellows is no more than 15 cm (6 inches) wide at any point, and it is no more than 35 cm (14 inches) long. If you’re design is much larger than this the bellows will be very unwieldy and difficult to use.
Trace your design onto one of your two boards. Fit that board over the other board and use your C-clamp to secure them one atop another. Use your band saw to cut the outline of the bellows. Smooth and shape the sides of the boards to your liking with the rasp. The four different roughnesses of the rasp will allow you greater control and detail in this task.
Unclamp the two boards and set one of them aside for the moment. Use your drill with the 1.5 cm (5/8 inch) bit to drill two holes into the other board. One hole should be in the centre of the handle and the other should be where the centre of the air chamber or belly will be. These holes should go all the way through.
Take the other board and draw a straight line across the nose where the nozzle would be. This line should be crosswise and about 5 cm (2 inches) from the end of the board. Cut the nose of the board off and glue it to its counterpart, the board that’s been drilled.
Use the 1.2 cm (1/2 inch) drill bit to bore a hole lengthwise down the centre of the nose, where the nozzle of the bellows will go. The holes should be centre to cut into both the board and the wooden block you’ve glued to it to emerge visibly out of the rear.
Cut a piece of leather 7.5 cm (3 inches) to each side and lay it over the hole in the centre of the bellows on the same side the wooden block has been glued. Tack down two adjacent corners to make you valve flap. It will pull back to suck in air when the bellows expands and cover the hole to prevent air leaking when the bellows contracts.
Fit the male-to-male compression pipe coupler to the brass flare nut and slide it into the channel you cut at the front of the board to create your nozzle. Glue the rear against the surrounding wood to seal it into place.
Cut another square of leather to create the bellows’ outer hinge. Fit the two boards back together so they fit just the way they did when you cut them. The block glued to the one board should line up to the board it was cut from. Place half the leather square on the wooden block and the other half on the board it was cut from and tack the square down into place. Four or six tacks should be sufficient. You now have a hinged bellows; all it lacks is the regulating thong and the leather “boot” which seals the air chamber.
Cut a thin strip of leather from the your scraps and thread it through the hole you drilled into the handle of one of the boards. Loop it around the other handle and tie it to set the greatest point at which the bellows can expand. This is the regulating loop and without one your bellows would rip when it expands.
Now cut the “boot” which will form the air chamber of the bellows. This is a very important step. The first thing to do is fit a likely looking piece of leather around the back and sides of the air chamber to make sure you’ve got the right size when the bellows is at maximum expansion. Cut out the rough shape, making sure that there’s a little extra room for error. A thin, high quality leather is necessary for this piece as it will need to fold easily as well as stay air tight. Once you’ve got the leather cut to the right size paint the edges with glue and push the boot into place. Drive a tack into the lips of the boot every half inch to ensure the leather stays attached and sealed to the wooden paddles. Allow it a full day to dry before testing.
You should be able to find the leather and vinyl scraps in a furniture and upholstery stores. Sometimes they will even pay you to take them away as they are often too small to be of use in furniture, but they are perfect for your needs.