Here is a demonstration of how it sounds.
Step 1: Materials Needed
-2" ABS/PVC Piping
-2" ABS/PVC Elbows
-2" ABS/PVC Couplings
-Pipe cutter (a hacksaw will work too, but it makes the edges rough)
Not Shown in Photo:
-2x4 and 2x10's
-2 1/2" Bore
-Power tools and screws
-Castor Wheels (Optional)
Step 2: The "Keyboard"
Step 3: Building the Base
Step 4: Paddles
Step 5: Assembling the Pipes
I got an equation from nate true that will give you the length of the pipe you need when you plug in the frequency: Tube Length (in) = (13300/(2*Frequency))+(Tube Diameter/2)
For the frequencies of the notes in the range of the piano go here: http://en.wikipedia.org/wiki/Piano_key_frequencies
My low note was number 16 (C2) in the list on the wikipedia page.
Remember, if a note is too sharp, it is too short. If it is too flat, it is too long.
Step 6: Finishing Touches
Please let me know if you have any comments or questions.