I've been learning about tuning reeds, by embarking on retuning a brass-reeded Lachenal tutor to concert pitch from old philharmonic pitch. I bought it as a wreck some years ago and have been restoring it intermittently - see lachenal_52313.html. I realise that retuning is hard, and tedious, and I'm likely to make mistakes, but I'd prefer to make mistakes on this instrument which will never be a great one. A famous physicist once said that an expert is someone who has made all the possible mistakes in their subject!
I've done a first pass on all the reeds, and now doing a second pass. It's all going reasonably well, except that I have three reeds which are within four cents of true pitch when blown gently, but when the pressure is increased slightly, they warble and go sharp. There was another like that, but by repeatedly tweaking the setting of the reed in the frame I managed to make it OK. However the remaining three (low Ds and B on RHS) are resisting my efforts.
So, does anybody have any hints for how to correct that scenario? I've already tried cleaning the edge of the reed and the frame. Note that this happens when the reed is in an external tuning jig, as well as when re-inserted into the instrument, so it's nothing to do with the fit of the frame in the wood slot.
It is of course quite possible that in my learning, I've manage to file the reed to a strange cross-section, so if nobody can suggest a solution, I could send the reeds off to Concertina Spares to be replaced or fixed, but I'd like to understand the cause of the problem and see if I can fix it myself if someone can suggest an approach.
In general, are there any hints on setting of reeds beyond the description in Dave Elliot's Concertina Maintenance Manual?