My G flute can hit about 2 octaves easily and 2.5 octaves if you push it. My D fife can hit 2 octaves. There are already a number of good sites out there on how to make flutes, but I thought I would add some of my experiences making my own flute collection that haven't been addressed.
For a primer of how to play a PVC flute check out my website: How to Flute
Step 1: Design
I made a G flute as originally designed and a CPVC D fife to which I also made a modified version. The G flute works great as is, but I was having a lot more trouble playing the fife. It was very difficult to reach into the second octave. Part of the problem I found was to do with the thin walls of the 1/2 inch CPVC. To create for thicker walls with the same pipe, I decided to add a lip plate (like those used on metal flutes) made out of a 1/2 inch CPVC connector.
I also made some original flute designs out of the same material as the G flute but higher pitched in the keys of A and C. These are both easier to play in the bottom octave, but take more coaxing to push into the second octave, especially for the C flute.
To make your own designs or to adapt these designs to different PVC tubing or drill sizes, the flutomat is a handy tool that automatically calculates the hole placement from the tubing specs, drill sizes and key you would like to play in.
Step 2: Construction
Step 3: Drilling Holes in PVC Tubing
I hold my pipes for drilling and cutting in a workbench which has two move-able table sections with a grove on their sides that can clamp together. If you don't have something like that, then a v groove or two pieces of wood spaced apart the right width will help to hold the pipe from moving around while drilling and cutting.
Which Drill Bit?
Either brad point or standard twist bits will do an equally effective job at a clean hole, but they are different. Brad point is easier to make an accurate hole with while they tend to be more likely to hurt the opposite side the pipe when punching through. The tip of the brad point has almost punctured the opposite wall on some of the holes I've drilled. I also tried using a drill press thinking it would be easier, but the feedback and control you lose with the drill press made it more difficult for me to use than a hand-held drill. It is a good idea to test out your drilling skills on a test piece before you invest time in your flute. It took me a few shots to get a clean hole the first time.
Step 4: Making the Embouchure
Start with about 45 degrees between the outer and inner edges. Depending on the size of the tubing compared with the diameter of the embouchure hole, it may not take much to reach the right angle, but it is critical to getting the most out of the flute. More filing is needed on larger pipes and on smaller embouchure holes to get to the correct angle. It may be easiest to go ahead and finish the rest of the instrument so it is playable, and then tweak the blown edge until you can get the best tone and control. But don't get greedy: you can always take off more material later but you can't put more on.
Edit: Thought I'd add a picture to clarify how to undercut the embouchure as I've gotten a few of questions about it. The flute will probably work without any undercutting, but they are much easier to play over a wider range with the right angle and a sharp edge. The blown edge is to the right in the new image. After the hole is drilled (the straight lines), undercut the side of the hole by removing the red material in the image. Make sure the edge marked by B stays sharp and the surface marked by A stays straight and smooth. Don't remove any material from the outside of the tube, only from the inside surface of the hole. After you're done undercutting the blown edge, the tube and hole should look no different from the outside from when you first drilled it.
Step 5: The Cork
My preferred cork material is, not surprisingly, actual cork. It looks professional in the end of the flute and doesn't swell or shrink and come loose when moist. This is what I used for my favorite G flute. The problem with cork is I haven't found source that doesn't need modification for it to fit 1/2 schedule 40 PVC. A standard wine cork needs to be cut down to fit with a plug cutter. This was difficult, labor intensive and frustrating. I also couldn't find any workable cork locally or sufficiently thick cork pads to cut plugs from
So, I tried wooden dowels. With a bit of a bevel on the end for easy entry and some sanding, a 5/8 inch diameter dowel fits well. I inserted the dowel to the correct depth I then cut off the dowel and smoothed the ends of the pipe and dowel to one smooth surface on the disc sander. This worked well for a while, but eventually moisture caused the dowel to loosen and fall out of the PVC.
This brought me to the rubber stopper from my local hardware store. The stoppers are tapered but to big to fit in the pipe without modification. To install a rubber stopper, I insert it as far as it will go, then cut of the excess with a wide chisel using a smooth slicing motion. This works fairly well, but isn't as clean or nice looking as actual cork.
For CPVC Flutes
For 1/2 inch CPVC it is probably easier to find cork stoppers at a craft store of the correct size (there were non large enough to fit the 1/2 inch PVC pipe.) I haven't tried to make a cork of either actual cork or the rubber stopper method for this type of pipe, so I don't know how well they work or how hard it actually is to find suitable material. Dowels are much more difficult to use for the 1/2 inch CPVC since no standard sizes fit. I had to turn down a dowel on a the lathe to get it to fit properly (although it hasn't loosened like some of the dowels in my PVC flutes.)
Step 6: Tuning Slide
The easier method uses the 1/2 inch connectors already available for the pipes. To add one of these, it only requires that you use two sections of tubing for the flute. One section of the flute, the head joint, has the embouchure; the other has the finger holes. The only tricky part of this design is getting the head joint the right length so it is within range of the correct pitch, when near the center of travel in the connector. This can be difficult due to the small range over which the tuning slide can move.
Although more time consuming, the acetone method can make for a better tuning slide since it can be as long as needed. The acetone softens the PVC so it can be stretched to fit on another piece of PVC. To start this method you will need acetone, which is sold as a solvent in the paint section of home centers. You also need a container that won't degrade sitting with acetone in it for a few days. Glass works well for this. The container should be as tall and narrow as possible so as to not waste acetone (once the acetone is used once, it is best that you dispose of it properly or store it separately rather than put it back into the original acetone container since it probably leaches all sorts of unknown chemicals from the PVC.)
To make the slide, I started with enough acetone in my container to submerge as much of the PVC as I wanted to stretch. The PVC sat for at least 24 hours before it was soft enough. At this point I took out the acetone soaked pipe and stretched it over another piece of pipe. I let the pipe dry in this position for another 24 plus hours before it was solid again at which point you can finish the flute as usual. You can stretch either the head joint or the body but it would be best to do this labor intensive process to which ever part you plan on sharing the most between other complimentary sections.