This is the High A hole on a WarMac chanter which had been carved out far too big and with rough edges. I had been told that there was no satisfactory way of filling it using glue or filler. But I went ahead anyway and found that the following method really does work. It looks drastic and.. yes, it is. It's certainly not for the faint-hearted. And I very much recommend practicing on a throw-away bit of plastic first. But it was either that or throw the chanter away. As it turned out, the procedure worked very well and the chanter went back into service in the band as good as any other.
I used a black heavy-duty cable-tie and melted it into the hole using a standard soldering iron. First I heated up the area around the hole to soften it up before melting the cable-tie material into it. Then I kept the soldering iron in contact with the chanter all the time while pressing the new plastic well into the original surface to make a good bond. I applied enough plastic to build up the whole area around the hole well above the level of the original surface. I also filled in the hole itself until it was significantly smaller than it was before.
Having left it for a while to go cold I then used a small, fine flat file about twice the width of the hole to flatten the whole area down to the original level. Then I used a round needle file to gently file out the hole to the size I wanted.
I then smoothed down the whole area with fine sandpaper and finally with fine grade wire wool.
The final stage was to rub the whole area down thoroughly with T-Cut (a car paint renovating cream) and buff it up to a polished finish.