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A simple steam whistle design for 1/4 scale loco Here is a simple steam whistle you can build with a few simple tools and copper tubing and fittings.

For a .DXF version of this drawing   CAD .DXF file

Saw and file the slots in the end of the tubing, the bottom of each slot is filed at an angle to make the wall of the tube taper to a sharp edge on the inside of the tube.  The width and length of the slots has an effect on pitch, sound volume and pressure required.

Before soldering the fitting and other parts simply assemble dry and adjust parts for best tone.
To assemble, clean and set the 1¢ disk in to the spring tube, it should fit without falling out. Now slide the center into the slotted end of the pipe and slip on the 3/4" fitting.
A 3/4" dowel with a few wraps of black electrical tape on one end will allow you to tune the pipe as a closed ended pipe. Once a good length is found with the correct pitch you can cut tubing to this length and add a top.
You can tune the pipe as an open whistle or a closed top.  A discussion of tuning pipes is beyond the scope of this page.
A closed  top can be made the same way as the spring ring and 1¢ at the other end.  A screw adjustable end should be considered.
A length of 6" to 8" of 3/4 tubing is a good starting point.
This design should work as drawn but you will want to "PLAY" with the position of the parts to get the best sound.

You only need about 1/2 to 1-1/2 psi to make it work. Changing the location of the parts and size of the slots will change the air/steam pressure and flow requirements.

If you have a lathe, a better solid inside part with radius on edges will improve tone and allow a lower note.

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