Here's a gif file showing a detail of the pattern I used to design the square bellows. (Note the pattern is different for a conical bellows.)

layout pattern detail

Dimension "A" is the width of the fold. Dimension "B" is the length of the inside opening of the bellows and dimension "C" is "B" - 1/8". Stiffeners are illustrated in gray tone. You need to have a 1/8" gap between all stiffeners in order for the bellows to fold properly.

In this bellows the dimensions are:

A = 1.00" (= width of corner fold)
B = 9.25" (= inside dimension)
C = 9.125" (= rectangular stiffener length...width is A - 1/8"...trapezoidal stiffeners formed by adding a 45-degree right triangle to both ends of the rectangular stiffeners.)
exterior dimension = B + 2A =11.25"
maximum extension ~ 24"
minimum extension ~ 1.75"

There are 15 pairs of stiffeners (30 total inches) for each of the 4 sides. This gives a comfortable extension of about 24" and the bellows compresses to less than 2" minimum. I planned the extension based on a dimension to get a life-sized, 1:1 magnification with a normal lens (~10.75") for the full plate format (6.5" x 8.5"). Thus, I wanted at least 21.5" extension and figured I'd need about 30% more length to achieve the proper extension. So 21.5" x 1.3 = 27.95" and so I rounded it upward to an even 30" hence the fifteen 1" pairs of stiffeners per panel. There is also an extra 3" of material at top and bottom to allow for attaching the bellows to a bellows frame which is then screwed onto the camera front and rear boxes.

For this camera (under construction) the inside bellows opening was designed to allow the use of an 8.5" square #6 synched Packard Shutter mounted internally behind a large 8" lensboard. This shutter has a opening diameter of 5" and will allow the use of very large barrel portrait lenses (e.g., 18" f/4 Verito, 16" f/3.8 Vitax, etc.) on the camera. That's the reason a 9.25" inside square bellows was needed. It had to clear an 8.5" glass plate (horizontally and vertically) at the rear of the camera, and allow for the 8.5" square Packard Shutter and air fittings at the front.

More to come...