Now that I’ve figured out the fipple, tuning is the next challenge. This site lists ratios to calculate the finger hole locations, but they are for “ideal” situations. There also is a link to a finger hole calculator. The calculator doesn’t seem to work for me. I think the walls of my flute are too thick.
I also tried to drill holes at regular intervals. This worked ok on the cherry flute, but not on the poplar one. The cherry flute was about 12 1/2 inches, with six holes, 1 1/4 inches apart, starting 2 1/4 inches from the end, not the blow hole. I was able to widen the holes to sharpen the notes and bring most of the holes into tune. The holes on the poplar flute 1 1/2 inches apart (the flute is 15 1/2 inches from blow hole to tip). 1 1/2 inches makes the holes hard to reach.
The most interesting thing about tuning is that there are so many factors, it is almost impossible to have an exact “formula” for the holes. You just have to drill and then tune the instrument.
You can tune the flute by making the holes larger. This sharpens the notes. I found that making the holes larger affects the other notes. I haven’t figured out which end to start, so right now I’m just using my guitar tuner and adjusting the holes.
Also, many hole layouts have some holes very close together or look like holes are skipped. These are for pentatonic tunings. With a pentatonic tuning, all the available notes are in the same key, so you can play anything and have it sound like music.