After I bought a pressure gauge, I found that my first bellows did not
maintain pressure as the demand for air increased. My first thought was that the pantagraphs weren't working
properly so I removed them and placed enough weight on the top plate of the bellows to get the correct pressure.
I knew that weights were sure to keep a constant force on the bellows. I measured the same drop in pressure
as the demand increased. After some experimenting, I found that the force needed to increase by several
pounds as the top plate dropped to keep the pressure constant. There is a certain amount of tuning you
can do with the pantagraphs to make the force not constant but there was no way I could make the output
force of the pantagraphs increase as much as it needed to. So then I decided to make new single fold
bellows with an internal curtain valve. When I designed the first bellows, I was afraid of trying to make
a bellows with folds with all the leathering of the corners. Now that I have a little experience working
with hot hide glue, I decided to give it a try. There is some information on making bellows in the books
but I got the most useful information from the following website.
The leathering turned out to be a lot of fun. I really felt like an organ builder doing it. The results
are a little sloppy looking but they work. The bellows crackle and pop a little as they go up and
down but hopefully it won't be objectionable.
Here's the top frame being glued:
I first used doubled sided tape to hold the ribs in position while I glued the first strip of leather:
I didn't glue the ends because they will go on the top side of the gussets in the corners:
Then I folded the ribs over and glued a strip of leather on what will be the inside edge:
The next two photos show the strips on the outside edges of the ribs:
I made some braces to hold the plates in the correct position while I installed the ribs:
And finally here are the gussets. One thing I learned is don't get any glue on your fingers because then it's really hard to push the leather down.
Here's what the bellows will look like when assembled:
Click here (2.1MB) for a movie of the curtain valve in action.
Here's the pulley mechanism for the curtain valve: