I have been planning on making a full size air raid siren, but before I invest the time and money into that, I wanted to test my design with a scale model. Much to my suprise, the scale model works if you spin it with a compressed air line! In this tutorial, I will step you through how to create the working scale model, or the mini air raid siren.
For the purposes of this instructable, I will have to assume that you have access to and operator's knowledge of a CNC laser cutter.
This is a complex assembly. It involves dozens of parts. As such, I am only posting the Illustrator file that I have already prepared to be laser cut. If you would like the CAD files, comment and I will upload them.
CNC laser cutter
Hot glue gun or wood glue
12" x 15" of 0.125" plywood
One 1.5" machine screw or bolt with 4 matching washers and 2 nuts
Step 1: Laser Cutting the File
Model size: If you want a larger model, scale the Illustrator file up by 200% and use 0.25" plywood.
Otherwise, proceed to your favorite laser and cut out all the parts. When removing the pieces, group them according to steps 3, 4, and 5, as it will make assembly much easier.
Step 2: Building the Frame
First we will assemble the frame. For this part, as well as parts 4 and 5, you will need a hot glue gun or wood glue. I opted for the former because I wanted it to dry faster.
Starting with one of the side pieces (the only frame piece that has 2 copies of it), begin with picture 3. Follow along until picture 7, at which point the whole frame should be fitted together. Then run some lines of glue along all the joints, and let it dry.
Step 3: Building the Rotor
For the rotor, you will start with the circle with the smallest inner hole (it also has 8 small holes around the inner hole). Glue one of the larger fins onto the cutout that marks where they go. Then glue a second fin on top of the first (see pictures 3 and 4). Continue this process and stack large fins 2 high on all 6 of the fin cutouts.
Next glue a circle with the smaller fin cutouts ontop of the first set, like in picture 6. Just like we did for the first layer, we are going to glue on small fins 2 layers high on each cutout. Finally, glue the last circle on top of the assembly you have built so far, then set the rotor aside to dry.
Step 4: Buidling the Stator
The stator will follow a very similar process to the rotor.
The first ring is the one with only 6 marked spots. Glue the long spacers 2 layers high on all 6 of the marked spots for the first ring. Then, do the same with the smaller spacers an the other ring.
This time though, turn the first ring assembly upside down, and glue the smaller space ring assembly on top of it face down as well. See pictures 5 and 6 for illustrations.
Lastly, I wanted this to be a functional model, so I sanded the inside of the stator to smoothen it so that the rotor wouldn't be rubbing on anything.
Step 5: Putting It All Together
Put 3 washers on your screw, then slide the rotor onto the screw. Follow this with another washer, and then secure it with a nut. Next, insert the back end of the screw into the hole in the frame, and secure it on with the second nut.
After the rotor is in place, apply some glue to the stator and glue the stator to the frame, such that the stator is around the rotor but does not touch it.
Use a compressed air line in your workshop to spin the rotor. Using my 50psi line, I was able to get a really loud high pitched whine. Next, Ill be using a 240 volts DC motor to power a 12" air raid siren, which will hopefully be much deeper and even louder, so stay tuned. :)