Willow whistles can only be made in spring and early summer, when the tree is growing strong. This job requires bright green twigs with long spaces between the bumps, or nodes, where the leaves come out. The fresher and greener and fatter and smoother the piece, the easier the whistle will be to make. A sharp knife is the only tool needed. Find a long space between the nodes and cut it out by rolling it between a flat surface and the knife blade.
A whistle whistles when a jet of air is directed at the edge of an opening in the chamber. Differential air pressure causes the air stream to oscillate on either side of the edge, somewhat in the manner of a fluttering flag. Make this edge in the willow whistle by first making a perpendicular cut through about one-third the diameter of the willow about 3A inch in from one end. Then cut down from the far end at about a 35-degree angle and remove the little chip.
To make the chamber, you need to take out the insides of the twig, and for this the green willow is very obliging. In the spring the layer of cells between the bark and the wood is rapidly growing and dividing, and it is very fragile. You can crush this cambium layer by gently rolling the willow between a flat surface and the side of your jackknife. Don't press too hard or you can crush or tear the bark as well. When you feel that you have rolled over every spot, place the end grain of the stick on the corner of something and push down firmly on the bark as if to slide it off. The crushed layer of cells should give with a snap, and the bark can be slid off the stick. If it doesn't give, you can try rolling a bit more. If it still doesn't work, it's the wrong time of year. The expression "clean as a whistle" is said to come from the pure whiteness of this inner stick.
Set the bark aside and cut the stick in twain by rolling the knife blade on it right where the first perpendicular cut was made. The shorter of the two pieces will become the ramp, or fipple block, which funnels and directs the air at the angled cut in the bark. Slice this short piece lengthwise, taking off one-quarter of its diameter on one end and angling to about one-half the diameter on the other. Push this piece back into the bark, larger end first, so that it will aim the air right at the sharp angle. Stick the other piece of the stick a short ways into the back end of the bark and you're in business. You can change the pitch of the whistle by sliding the long stick in and out.
Once you get the hang of it, you can turn out a whistle in about a minute. This was our fourth day with nothing to do, and it wasn't long before every one of us was armed with a brace of willow whistles and attempting to play them all at once. They are shrill devils, and I guarantee that if you get twenty people all tuning and playing willow whistles while simultaneously rattling away on their multiheaded whimmy diddles, you can crack even the most hardened mountain forest rangers. Within an hour they had scrounged together a set of horseshoes and a volleyball, putting an end to our whittling diversions. The willow whistles had dried out by late that afternoon and were unplayable. We later traded all the whimmy diddles to one of the rangers for ramps (wild mountain onions) and venison. A few of us were even called on that evening to help put out a fire— and we just about beat that barbeque grill into the ground.
"The Woodwright's Companion: Exploring Traditional Woodcraft" By Roy Underhill
© 2012 The University of North Carolina Press