As promised: no details, or only very few...
It is based upon a few measurements on old bellows plus a few photos of Geoff’s mould, as I saw it in High Bradfield in 2010. It illustrates very well one of his sayings (and my favorite one): “None of this is really difficult – there is just so much of it!”:
The mould’s dimensions are based on the assumption that the “peaks” are 20 mm high (with 45° slopes) and that the distance between the “valleys” is 40 mm.
There is a lot of material thicknesses to take into account: an “inner hinge” of cotton band on the inside of the valleys, another on the inside of the peaks, a cotton band on top of the peaks, and a leather band on top of that. And then there is the thickness of the card board. So – what’s the height of a card? All this led to the writing of an ActionScript (Flash) program to calculate just that:
The first (and so far only) bellows was a replacement for an old 56-key English concertina. Here it is, halfway:
The wood & elastic band-thingies add pressure on the critical ends of the gussets after gluing them on (with “Fiebing’s Leathercraft Cement”):
Finished:
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