Introduction: Soft Pneumatic Wind Instrument Key Concept

This instructable will guide you trough the process to make a proof of concept for a novel way to make a musical instrument key.

It will guide you trough :

1 - The idea, where the working of the proposed "technology" is explained.

2 - The supplies you will need to replicate this proof of concept, or to get to work with the technology yourself.

3 - How the drawing this in cad was done

4 - The printing of the needed parts

5 - The making if the thing trough using the moulds drawn in step 3 and printed in step 4

6 - The proof of concept, the testing.

7 - Thoughts about where to go with the technology from here


Step 1: Idea

Few years ago I did some experiments with inflatables. I started with human sized bubbles. In my search for information I discovered soft robotics. After playing around with it (see the gif of a soft gripper) I wanted to do something with the technology that is closer to my interests than pure robotics. This is one of the ideas I had to use the soft robotics techniques in other settings.

The idea is quite simple.

A key is made out of a hollow chamber filled with air. This key is connected to an actuator that is placed over a hole of a wind instrument without obstructing the airflow. If you press the button, the air from the button is pressed in the actuator and the actuator covers the hole. This obstructs the airflow which makes the tube longer so the tune of the wind instrument is lower.

That`s it basically

Step 2: Supplies


  • a computer with fusion 360 (or other cad software)
  • a 3d printer (or a 3d print service)
  • silicone caulk gun
  • plastic pot (to mix)
  • mixing spatula
  • protective gloves
  • protection for your workspace (old newspaper)


  • 3d print material (I used PLA)
  • Silicone caulk (best pure silicone)
  • corn starch
  • Paint as colouring, if you like

Step 3: Draw in Cad

If you want to make a hollow thing with moulds you will always need 4 moulds. These 4 moulds produce 2 parts that will be added together later.

To draw this in cad you can best start with the model that will be the finished part. Once the finished part is drawn you have to split it. It is best that you think in advance where you are going to split it. After the split you can draw the 2 moulds per part.

It's not easy to write down how to draw something in CAD. In the pictures I have attempted to write a little guide with the steps I took. In the pictures the guide is written on screenshots. It will give you an indication of how it was done.

The best way to learn the steps undertaken to get to the parts is to take a look at the parts history in the original files. In the link provided here You can look for yourself how the moulds were drawn.


Step 4: Print Moulds

The moulds can be printed on a standard FDM printer (I use the geeetech a10 but forgot to take pictures). The moulds were drawn is such a way you will not need any support material.

Since the finished part will be a functional one you can print it quite coarse. infill between 20-50% wall thicknes of 0,8-1 mm. As already mentioned there is no support needed.

Attached are the stl files for the moulds.

If you have a 3d printer these prints will not give you any problems. If you are a total beginner you can start here .

You can also choose to outsource your print.

Step 5: Fill the Moulds

I made my parts in oogoo. Oogoo is a mixture of silicone chaulk and corn starch.

here you can learn how to make oogoo

Before you start you have to know that oogoo is quite messy. Best is to wear bad clothes and to use gloves and protection for you workspace. (I once had some oogoo om my pants. It sticks, looks like you've sneezed on your pants. I tried to get rid of it with silicone lubricant. It worked, but now I can't get rid of the lubricant and my pants keep slipping off :)

The moulds are filled with a 4 to 1 mixture (4 part silicone 1 part corn starch). The best is of you overfill the moulds. the excess will come out of the air holes and al the other ......... After the upper part and lower part are ready you can glue them together with some more mixture (. Watch out that you don't glue the middle of the actuator circle, otherwise the key will not work.

Take a look at the guide in the pictures. It will guide you through the moulding process. There is probably still a lot wrong with it, but it is a start.

Step 6: Test Your Work

After you have finished the assembly of the parts you can test the key.

I used a plastic soprano recorder for the test.

added the key with some rubber bands to the recorder.

It works .... sort of

Step 7: Next Steps

The next steps for this project now a "proof-of-concept" (proof of idea) has shown that this is possible will be to make a working prototype instrument. There are no keys on a soprano recorder so it makes no sense to add more there. A saxophone on the other hand has too many keys and is not suited for a prototype.

The Bass recorder would be a good prototype candidate (the great bass is also a great candidate) The first drawing is a way the upper three holes of the great bas could be made. The second drawing gives an indication of how it could be done.

The holy grail is the saxophone. It would be great to make a part with all the buttons and keys already included. This could be added to the saxophone body. It will probably not be cheaper to produce nor will it improve the sound of the saxophone. But it will be a lot of fun to try.

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