The bellows hex-frames
The bellows frames and the end box frames are identical, apart from the fact that the finished bellows are wider across the flats, by this amount:

(leather thickness+cotton band thickness)*2

Practically, leather+cotton = 1 mm, so a desired 6” (152.4 mm) across the flats means frames that are 150.4 mm across the flats.

This means that the end box frames need an extra 1 mm of something – as described
here. In this case I have chosen my trusty 0.4 mm aircraft plywood plus 0.6 mm birch veneer. It doesn’t matter which - they are going to be black anyway.

Material
I am very fond of aircraft plywood, so it will be 6 mm ply for the frames. It’s dense and hard, almost like a ceramic material – if you ding two frames together it has a nice “ring“ to it ;-). And yes, it’s probably a little heavier than other woods.

As hex as possible
The joints are not the usual 60° – it is an interlocking design that I call the
Gammage Joint – a concept I got from a UK mate of mine, Richard Gammage:

GammageJoint

Very neat. I made a sort-of-adjustable mould to ensure I could control everything during gluing:

Frame mould

It is “calibrated” across the flats in all three angles with a 150,4 mm aluminium block.

Angles, angles
Now, all this 30°, 60°, 120° leads to the question: what is the length of a frame side, when the width across the flats is X mm? I realized that I would be asking myself that question many times. Enter the next ActionScript program:

Hex calc

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