For those that made a flute instrument, how did you make your hole smaller? I tried hot glue, wax and both of these methods didn't work that well because it only stuck for a few minutes. I might consider using PVC glue.
You could put tape over part of your holes, like cover the top half of the hole with tape. I don't believe the holes need to be perfectly round per se, so you can just put tape over part and adjust the position of the tape as you tune.
2018: Hovercraft, Thermo, Coaster, Solar System
2019: Thermo, Circuit Lab, Sounds, Wright Stuff
2020: Circuit Lab, Chem Lab, Wright Stuff, Machines
It's not science if you don't glue your hand to it at least three times.