A question that occurred to me as I was plotting the widths of David's reeds is how did they manage to cut reeds to fit these slots so accurately? I've done a lot of sheet metal work over the years, predominantly in association with custom research electronics equipment. My experience with cutting metals on guillotines and shears is that it's pretty hit and miss because of creep, and you end up with distorted strips - usually with a twist, and often with a compressed and sloping edge. Not my ideal starting point for a precision end product! And we mostly worked in aluminium, brass, copper and mild steel, while the steel for reeds is much harder.
Now, I imagine there's a fair amount of filing in the final fitting, but obviously one would like to get pretty close from the start. So, what's the trick?