The Indian flute is unique in that it has two chambers, the sound chamber and a Slow Air Chamber.
Start by setting the router bit to 1/2 the diameter of the bore.
Most of what I've read calls for 7/8 inch bore. I haven't been able to locate a 7/8 router bit, so I use 1/2, 3/4 and 1 inch. 3/4 shown.
There's a law of physics that limits the length of the bore to 18 times its diameter. Longer than that and you get no sound.
Charles W. (Charlie) Brown said:
Finish the Slow Air Chamber.
Pick the side with the best figure and rough out the transition holes. You only need to mark the spot where they exit. These can be 1/2 the diameter of the two chambers. I'm using a 1/2 inch chisel here. Because moisture in the breath condenses out in the SAC, waterproof both sides and the mouthpiece hole with lacquer, shellac, urethane, etc. sand the sides smooth so glue will stick.