Tone holes - aargh!

I used a small drill bit on an extremely low speed to drill the initial positions of the tone holes at the suggested spots on the whistle. I was a bit concerned about the large spacing between the last and second-last holes, but I thought it best just to follow the basic instructions for my first attempt (the pdf does include many suggestions for customisations, including how to change hole spacing by compensating with different hole sizes).

I then drilled each hole out to 4mm, then 8mm, the diameter of the smallest holes, and then enlarged each larger hole after that. A slow speed was very necessary, as the drill bit would grab and then dive towards the other side of the tubing as soon as it bit into the plastic.

The last tone hole, which produces the note E, needed to be enlarged by about another mm, as the sound of the second octave E was very weak and breathy. I didn't have that sized drill bit, so I used sharp little scissors to scrape around the inside of the hole until I got it right.