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How to smooth the apex of the bellows?


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Hello

I'm trying replace the synthetic leather gusset for some concertinas.

That is success, but I don't like the finish of the bellows apex.

That model is like traditional Wheatstone, Lachenal, other modern concertina makers.

These instruments have leather tape glued to the bellows in a smooth circular motion.

 

I first modeled was Stagi, which simply folded in leather tape flap, I repaired for the first time.

The second time I opened flaps in two and folded it.

I use 20mm wide leather tape.

How to smooth the apex of the bellows?
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Genepinefield

 

It may be that the problem is you are using synthetic leather. How stretchy is it?

 

When I have fitted new top runs, I have used skived goatskin leather, and this can be easily shaped over the apex by puling it to stretch it slightly, and using the thumb and forefinger in a backwards and forwards motion over the curve until the creases disappear. I usually fit the top run all the way round first, then come back to each apex in turn and work it flat while the glue is still wet. Using a cloth damped in a little warm water helps with the flattening and cleaning off surplus glue.

 

The leather is skived to 0.5 to 0.7 mm.

 

Also 20mm width seems a bit big, From memory I would use about 12 mm wide

Edited by Rod Pearce
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The process is called binding, 'top binding' to be more precise. this is a strip of leather which is about 18mm wide, and about 0.6mm thick. However it does not stop there as both flanks of the strip of binding are skived over around 5mm each side on the underside of the leather. This skive leaves around 8 mm of full thickness down the centre, and tapers off to around 0.22mm thickness along each edge. This double tapering of the cross section of the binding makes for a stretchy strip with less leather bulk along the edges.

 

I apply adhesive along say 100mm of the binding at a time, then stretch the binding along the top of the flat of the fold but without full pressing the skived area down. When I get to the corner between two flats I continue round the corner and part way along the next flat. I smooth down the middle third of the length of binding, both sides, along the two flats either side of the corner leaving the corner binding flanks still standing off the fold/ gusset faces. Finally I smooth the binding down over the gusset on each flank spreading the excess bulk of the leather back along the fold flats. This distributes the bunched skived edges back along the corner radius and part of the flats. Thus there is no need to do anything fancy with the binding over the gussets/ corner

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Good advice from Rod and David.  I would add one tip. My secret weapon is to use a damp, 100% woolen sock, rather  than the cloth Rod mentions.  It does a great job of smoothing, pressing, and removing excess glue without "catching" the leather and shifting it the way a regular cloth sometimes does. 

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Thank you very detailed advice!!

I'm using goat leather tape, skived 0.2-0.3mm 20mm wide.

I cut the tape by myself, just along the direction from the head to the tail, so stretching differs depending on the part.

I need practice of this procedure, so I now make practicing bellows by stagi method. that use children's handmade workshop cardboard.

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