I have a German Meyer flute from 1880 which is in good playing condition, but unfortunately plays slightly flat of A=440. It’s not really a problem with other tunable instruments, but I find it challenging to keep in tune with the concertinas and accordians. I can manage being in tune, but I feel I am compromising tone for in-tuneness. I’m wondering what can be done short of doing major surgery on the flute to rectify this problem?
Arbo
Hi:
There is a couple of things that you can do:
1-Do all the tone holes a bit bigger
2-Do the embouchere hole a bit bigger.
You can do it with sandpaper, very carefully and slowly, trying to keep the instrument in tune with itself, and preserving the undercutting.
At the end of the process you should to polish the inner of the tone holes/embouchere hole.
I have done the process in several flutes and it works. Be a good observer before do the job and take a lot of care.
S. Moro.
Arbo
The easiest “Tweak” to raise the pitch of a slightly flat instrument is to employ an old Bagpipers trick. Insert a long narrow straw(bamboo?dowel?)inside the bore to decrease the cubic area and raise the pitch.
If you decide to have it “fixed”, I suggest increasing the length of the tennon joint for a shorter bore. If you want to switch back, the simple addition of some brass/silver “washer” shaped shims around the tennon will restore the length.
Speaking as an uilleann piper, we use rushes to flatten a chanter or regulator note that’s too sharp, but that’s because of the wierd physics of the double reed.
What you’re suggesting for a flute might just work, though, and I’m curious to learn of the results.
I just gave the rush concept a try. I used the Bb fife that sits next to my 'puter and thin brass rod (sorry, don’t recall the gauge), and almost no discernible difference. Then a chopstick, thick end at the bell, and there was a distinct difference (sharper). I thought that the chopstick, thick as it was, would make it quieter, but it didn’t seem to, much. I tried it the other way, pointy end at the bell, and the bell note and overall intonation was bollixed up. Interesting. I imagine conical and straight bores would have their own quirks in this matter.
Then a chopstick, thick end at the bell, and there was a distinct difference (sharper). I thought that the chopstick, thick as it was, would make it quieter, but it didn’t seem to, much. I tried it the other way, pointy end at the bell, and the bell note and overall intonation was bollixed up. Interesting. I imagine conical and straight bores would have their own quirks in this matter.
How did you affix the chopstick into the flute. And by ‘bell,’ do you mean the foot end?
Arbo
Yes, Arbo, the foot end. I didn’t affix it; I just stuck it in there to see what would happen, and really didn’t take into account its precise position. It was mere idle curiosity and not very scientific, but it worked.
Best,
N
Okay, I’ll give it a try. My initial concern was holding the flute level while plaing in a session (pints vs gravity thing?) and what might happen when excited about a certain tune the boxes might be playing…
(by the way, what happened to you in that photograph?).
Arbo
As for keeping it in place and specifications, I’m sure that Tom Hastay would be better suited to advise you. Remember, it was a straight-bore fife, and I just ran thru the scale, so the gravity/pints thing wasn’t an issue.
As for what happened to me in my picture, that was a textbook case of the gravity/pints thing: more pints, less gravity. 
To be “specific”
A long narrow dowel rod of consistant thickness running the entire length of the bore, from plug face to bore end, would be best. Placing a small dab of “permatex” sticky putty at both ends will hold it in place. lay the dowel opposite the toneholes. You may need to try different diameters for a “perfect” fit because I don’t know how flat your scale is. A litttle bigger/sharper is better so you can use the tuning slide for “heat correction”.
I made this suggestion as an alternative to permenant modification of an historical antique. Too many antique instruments are modified and ruined.