As I keep forgetting how to do it, I have written up a simple method for designing bellows graphically. The method allows for basic bellows with different tapers on the top/bottom and sides etc. as well as rectangular or square bellows. The approach also will let you start with one depth of fold, and end on another; the example bellows I have used for the write-up start with a 10mm fold depth and end with a 5mm fold depth. It is also possible to change the fold depth however you like along the length of the bellows: my 8x10 bellows start with a 25mm fold, increase to 30mm and then reduce to a 15mm fold.

A PDF file of the design process is here.

Best regards,

Evan