This is a method to create a simple double reed from a drinking straw, for use in a shawm / bagpipes / oboe / bombard.
Step 1: Cut a length of drinking straw
The diameter of the drinking straw should match the diameter of the top the bore of the instrument as closely as possible.
Commonly available drinking straws come in appximately 4-6mm sizes. There is apparently such a thing as a "stirring straw" for alcoholic drinks. which is about 3mm. I've found some straws of this size sold as stalks for balloons.
Step 2: Dunk in boiling water and squeeze tip
The hot water makes the straw malleable. Squeeze it so the tip is flattened.
Step 3: Sandpaper tip
Draw the tip of the straw over a piece of sandpaper. Do both sides of the reed. In the picture, I am drawing the straw to the left over the sandpaper [while holding the sandpaper where it is with my other hand].
Experiment with different angles.
If the straw is stiff, it might need a shallow angle from horizontal and lots of passes. If it's lightweight it might just need a few at close to 30 degrees from horizontal.
The straw will now produce a noise if blown like a double reed.
Step 4: Wrap straw in brown packing tape, leaving a small area near the tip exposed
The pitch the straw produces should be much higher. The pitch needs to be higher than the highest note you need to play.
I think this works because the stiff packing tape only lets the straw vibrate near the tip. The less of the tip is exposed, the higher the pitch.
Step 5: Refinement
If the required diameter is very small, try slitting the straw part-way along its length, so that the end inserted into the instrument can shrink to fit.
Sand the tip some more to work on the tone. Trim the tip back a tiny amount to raise the pitch, if it isn't quite high enough.
Step 6: Play
Print a shawm using the 3D printing technology of your choice. STL files can be found here. Insert the reed you just made, and play.
The reed needs to make an airtight seal with the instrument, or it may squeak. This might require a little extra tape to pad out the diameter, and some cork grease.
For the upper register to be in tune with the lower register, the length of reed extending out of the instrument needs to be correct.