Hear the CPVC Chromatic Panpipe
This project was done through experimentation of pipe lengths and their range capability. I used 1/2 CPVC because it was the smallest, thinnest walled form of pipe that would be available to anyone. I made the plugs adjustable so I could fine tune it. I determined the lengths by making a test pipe longer than the pipe listed below. By sitting at the piano and sliding the plug up and down I figured out the approximate locations for the separate note pipes. I would have preferred to do this with my tuner, but I didn't have it at the time. The piano setting are close enough though. If you have a tuner, I would fine tune them using these dimensions as your starting point.
Each note pipe is rounded at the top to be comfortable against your lips. It may very well have something to do with how well the pipe sounds too. I only listed the scale lengths for C4 (middle C) to C6 because anything above or below that became to difficult to resonate. In fact, when you approach the limit on either end it just gets harder. That's why I made mine in a scale from G4 to G5, right in the middle.
I made plugs that were both flat and concave. They both worked fine but in the end I convinced myself that the concave ones were better. These would be difficult to make without a lathe and the proper tools, so I suggest cork from the same hardware store where you picked up your pipe. Even without the concave surface, it should work fine. My plugs were made from plastic rod stock. I say this because if you use wood instead of plastic, moisture may it expand and crack your tube or shrink and just fall out. Do not use wood for any of your wind instruments unless you are prepared to properly treat the wood (and maintain it for years to come).
I made the holding device out of solid aluminum. Again, this would be very difficult without a machine shop. However, it's not necessary to make it that way. I would suggest wood for this since it's not going to be getting wet. Use solid wood not laminated or your tightening screws will wear out their threads too quickly. I would also suggest using a screw or bolt with a larger thread for the same reason (you could just glue them in place instead).
You'll notice that the picture I provided doesn't match the drawing. That's because this is the first and only one that I have made and wasn't really happy with the "in-line" location of the pipes. It made jumping back and forth between notes difficult. The drawings reflect a more practical way of arranging the pipes for speed of playing.
Lastly, this whole thing was made as complex as it is because I wanted one holding device and the ability to interchange various note pipes. If you're interested in making a simple panpipe, the only useful information here is the note pipe length and their placement next to each other. Almost everything else can be done however you like.