What angle?
One of the important characteristics of a concertina reed (frame) is that the walls in the slot have a slope:
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This allows the reed to evacuate air faster, leading to good dynamic range and less risk of “choking”.
It’s another hand job - involving a small file that has been planed down to 1.2 mm and smooth on three sides. Also involving marking the inside of the slot with a felt-tipped spirit marker and a bright light... should be interesting...
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