Date: Mon, 09 Sep 1996 14:40:22 -0500
From: Hans Mikelson <hpm@cray.com>


This document may be given away but not sold without my permission.

Here is how I've been making some PVC recorders or end-blown flutes.  
I use 3/4" electrical conduit PVC because it is only $1.50 for 10'.  
Cut off a 22" section and sand it smooth on both ends.  Next make 
the mouth piece.  It looks something like this:

   <--1"--------><-1/2"->
   --------------           -----------------------
   |            |          /  PVC angled edge
   --------------         -------------------------
3/16"-1/8"  -----Air--->    
          _______
    _____/  Wood|
   |       Dowel|
   |       Plug |
   ------------------------------------------------
   |                       PVC
   |
   ------------------------------------------------

Figure 1.

Use a power drill to make a slot in the PVC about 1" in from the 
mouth end.  Drill a couple of holes next to each other and then work 
the drill back and forth until you are able to form a slot.  Next 
work the drill at an angle until you have a pretty good angle on the 
side opposite the mouth.  Blowing against this edge is what makes 
the sound.  Make sure it is a clean edge.  Make the width of the 
slot about 1/2-2/3 as wide as the bore or inner diameter of the PVC.  
Clean up the edges with a triangle file, Xacto knife or sandpaper.

Cut a wooden dowel to about one inch length.  You may need to sand 
it to get it to fit into the PVC.  Sand one edge flat and at a 
slight angle so that the mouth end has a wider opening than the 
inside end.   The air must hit the angled part of the PVC about in 
the middle or you won't get any sound.  You may also need to thin 
the PVC above the opening in the dowel.  Put the dowel into the end 
of the PVC and blow on it.  If it does not make a sound try blowing 
harder or softer or at different angles, try repositioning the 
dowel, turning the dowel around or thinning the PVC above the 

opening in the dowel. 

Next drill the holes.  So far I have had bad luck with hole 
placemnet.  If the holes are too small they will sound too breathy.  
You may be able to tune slightly by making the holes larger so make 
them small at first.

The effective length of a tube with no holes is approximately length 
+ bore/2 because the vibrating column of air extends beyond the end 
of the tube by about this much.  If a hole is smaller than the bore 
than the vibration of the air will extend beyond the hole by some 
distance flattening the expected pitch.  Open holes down stream from 
the hole let air out and so they sharpen the pitch.  Closed holes 
also add a correction factor.

After going through all of these calculations and carefully drilling 
my holes I found that the pitches were not very close to what I had 
calculated.  It is almost as easy to just go by trial and error 
making small adjustments.

My current project is to build a multiple end blown flute consisting 
of three of these each with three holes.  The largest will be tuned 
to A, Bb, B, C.  The next C#, D, D#, E and the smallest E, F, F#, G. 
This should look similar to the following:
    _____
   /_____\
   | | | |
   |U|U|U|
   | | | |
   | | |o|
   | | |o|
   | | |o|
   | |o|_|
   | |o|
   | |o|
   | |_|
   |o|
   |o|
   |o|
   |_|

I'm currently working on perfecting the mouth piece.  This should 
play a C major chord when played with no fingers down.  The C minor 
chord would be first hole on tube 2 etc.