Friday, June 26, 2009

Bellows in shape

There are three most important measures you need to know before making bellows.

1. the opening size of front/back frame.
2. the rib width.
3. the length when bellows totally unfolded.


As for a bellows for 4x5 format, the back opening should be 90x120mm in standard size, but sometimes it changes a little bit, depend on the cameras, there always a frame pasted on it, to fix the shape and fix the back into back stand of the camera body.

I choose 95x120mm as back size in my Polaroid 110B conversion project.

And the front opening, depend on the front frame. The frame, with a round for lens to go through, and four tiny hole for screw, to fix to the front stand. For those old folders, there always no screws for the frame, just used glue.

In the pictures below, you can see one of my favorite folder- Kodak No.1 special, and a bellows tear from 110A. folder had been replaced old ragged bellows into my silk one, shows its quality under the sun.

From Drop Box


Now as an example, let's assume the rib width is 7mm, and the length of bellows is 140mm when totally unfolded. Measure your front and back opening sizes, and draw them in graphic program, I use CorelDraw if you asked, thank you. In this example, the front/back frame will be 60x67mm, 95x120mm.

From Drop Box


Then add the rib size for them, 7mm in rib width is common for most bellows under 4x5 format, remember to chamfer on each corner. Outer size now became 74x81mm, 109x134mm.

From Drop Box


If you ask me why it is 7mm in width? Then it relates to trigonometric function I guess. You see, the width of bevel edge comes from the sum of the square of two other sides as in pictures below, nearly 10mm, very easy to draw for the days when all things need to be done in hands, that's why.

From Drop Box


Now connect the outer edges of the two correspond sides of front and back opening, form a ladder-shaped, you need two of these, showed in green and blue color in picture.

From Drop Box


then turn the horizon one into vertical, and right-aligned with the other. For next step, two shapes meet each other with their end points.

From Drop Box


Using the meeting point as center of circle, draw a circle, radius is what your bellows' length, in here, radius is 140mm.

From Drop Box


Then stretch two ladder-shape to left, make their side extended just as long as radius of the circle.

From Drop Box


This ensures that two ladder-shapes will have the same length in bevel side. You can skip this if the bellows got the same size of front/back opening.

Now the time to draw ribs.

We set this bellows in 140mm in length, so we draw 10 circle side by side, from the tip where shapes meet to the end of big circle, in 14mm diameter.

From Drop Box


And then change circle into rectangles.

From Drop Box


all we need is half part of these rectangles, cut the upper half, then we rotate them, align the edges of the shape.

From Drop Box



From Drop Box
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