The leather working handbook from,..
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her name escapes me, but I think it's English
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...anyway, she describes an intetesting method I've not used yet.
Instead of a piped welt as describe above, she cuts a narrow strip. I guess it would want to be at least 2 or 3 times the thickness of your seam.
But one edge of this strip is sewn first to one panel, right sides together, then the other edge to the other panel, also right sides together.
The second seam might be much harder by machine, than hand, because of the clearances needed for foot or roller.
But you end with the look of a softer welted seam. I'm intrigued by this technique, but haven't tried it yet.
A little test corner would reveal practicality.
Anybody ever used it?