Bellows frame detail

[wunks]

I'm contemplating a modified Jeff duet prototype build starting with a nice pair of 6" Shakespeare ends I purchased not long ago.  I have a woodworker friend who is interested and feels capable with his skills and tools of doing a first rate job.  We're going to start with the bellows and frames.  I've looked at some of the very helpful online tutorials but find nothing concerning how the inside edge of the frame is modified to accept the bellows themselves.  All the best quality boxes I see have some degree of rounding or chamfer and a truncation of the corners to make a nice transition.  Is there a standard for this and how are the bellows cut to fit?  Also if the ends and action board frames are 6" the bellows frames must be slightly shy of that to account for the thickness of the leather.  Is that correct?  One method that seems to have been used on my own instruments is to use a veneer strip to come up to the finished dimension.  Any suggestions will be appreciated....🙂

Edited July 17 by wunks
sp.

[alex_holden]

17 hours ago, wunks said:

I'm contemplating a modified Jeff duet prototype build starting with a nice pair of 6" Shakespeare ends I purchased not long ago.  I have a woodworker friend who is interested and feels capable with his skills and tools of doing a first rate job.  We're going to start with the bellows and frames.  I've looked at some of the very helpful online tutorials but find nothing concerning how the inside edge of the frame is modified to accept the bellows themselves.  All the best quality boxes I see have some degree of rounding or chamfer and a truncation of the corners to make a nice transition.  Is there a standard for this and how are the bellows cut to fit?  Also if the ends and action board frames are 6" the bellows frames must be slightly shy of that to account for the thickness of the leather.  Is that correct?  One method that seems to have been used on my own instruments is to use a veneer strip to come up to the finished dimension.  Any suggestions will be appreciated....🙂

 

You can see the transitions in this photo.

 

I use a 3/4" radius on the bellows side (draw around something that's 1 1/2" diameter) and sand it to make a pleasant transition from the rounded corner on the bellows side and the almost-sharp corner on the action box side.

 

I usually make the outer across-flats dimension of the bellows frames about 1/16" smaller than that of the action boxes to account for the fabric and leather thickness.

 

The bellows cards are made to be the right width to fit the frame so there is a slight gap between them when the bellows are fully closed.

 

A tip for gluing up the bellows frames: I make them from spruce, which is strong and light, but the end grain soaks up glue like a sponge causing glue starvation in miter joints. I find I get a much stronger joint if I size the ends first. i.e. paint some thin glue onto all the joint surfaces, wipe off the excess, and let it dry, then lightly sand the surface before doing the actual glue-up. I also put in a bunch of splines made from 1/16" hard maple to reinforce them; possibly overkill but I have repaired some vintage instruments where the bellows frames came apart and I don't want it to happen to one of mine.

[wunks]

Just what I was looking for.  Thank you.