"just finished my first bellows - yep, its a chore indeed - especially a pyramid style (non-square) type - if your doin it mathematically there is only one other duplicate of each strip - takes aaaages to cut them all -"
Wait until you make a odd-size bellows (4x10 ; 8x20);-)). It's much easier just to draw it out full size and use standard size pleats (2 ribs=1 pleat) that way the corners match up. Just remember the growth rate from front to back X1/2 per panel AND the growth rate per pleat X1/2 per rib.
Now to throw the monkey-wrench into it: if you use the same size pleats the full length it may bind on the frame with front tilt (Korona; Agfa/Ansco; converted Kodak 2D) and it will vignette in the rear SO you have to allow for an inside taper by changing the size of the pleats. Now you get to work with 3 tapers, inside and outside, front and back; AND how they fold-up. The math goes out the window at this point and you need to draw it out with a compass and fine graph paper.
Yes, making a bellows is a major PITA but once the design is done, you can make 1,000 of them.