The plastic needle cap only needs slight modification to become an air channel.
Cutting the sounding hole is easily done with a sharp X-acto knife.
For those who are shocked by drug use associations with syringes, think of cannons to plowshares, or doctors who save lives. Better yet, just think of them as plastic tubing.
Be sure to check out the MP3 sound file in the last step to hear how the slide whistle sounds. This is a fine little musical instrument that only costs 25 cents to make.
Step 1: Remove the Needles
The protective caps pull straight off, and the needle twists off. Pull the cap slightly off, to free it, but use it to grab and untwist the needle from the end of the syringe. When you get the needle free it can easily be removed from the cap and placed in a secure container for storage or disposal.
I still haven't found a good use for the needles, but I hate to throw them away. It amazes me how they can make such tiny metal tubes in the first place! I could never make them myself.
Step 2: Cut Off the Ends of the Needle Caps
When you are done, the caps are open-ended tubes.
As far as I can tell, both the syringe bodies and the needle caps are made of polyethylene plastic. The cap tubes will later be heated and press fitted to the syringe bodies. I am finding that different syringe manufacturers sometimes make slight modifications in their designs. If the syringes you get have needle caps of a different kind of plastic, you may have to shape them by some means other than heating. Let's hope you are lucky and they, too, are made of polyethylene plastic.
Step 3: Cutting the Sounding Hole
Having the dowel inside on the first cut helps keep yourself from accidentally cutting down too far.
After the two basic cuts, I dress the hole up as needed with the tip of the X-acto knife.
Step 4: Heating and Placing the Air Channel Tube
Heat the tip of the air channel tube on the bottom side only, where it will press against and conform to the shape of the end of the syringe. This takes a little practice to get consistently good at it. It is better to not heat it enough and have a second try than to butcher it with too much heat the first time. I was lucky, and had 40 successes out of 40.
Carefully soften the plastic and press the tube down where it belongs on the syringe body. Aim for the angle you see in the photos, and placement at the beginning of the sounding hole.
I used sections of electrical tape cut in half lengthwise to tape the air channels to the syringe bodies.
Step 5: Hear the Slide Whistle
Low notes are with the plunger all the way down. High notes are with the plunger closer to the sounding hole. Between the two extremes, there are an infinite number of notes. Have fun finding the ones you are after!