Hi. In this video I'll show you how I built my air raid siren.
So what inspired me to try and build a siren
was when I was experimenting with building a blower for my dust collector.
It howled a lot like a siren already so
why not build a fan that's designed to make maximum noise instead of minimum noise.
I knew the way to cut the hub all concentric with the shaft
And I figured out a dangerous way to do that on the table saw.
It worked out OK.
The hub fits exactly into a hole the size of my largest forstner bit.
I used a large nail and a key to lock the hub onto the shaft.
Here's gluing up the first layer of the rotor.
Now spinning up that rotor and see if it works.
Holy shit.
So, I could never find the part that flew off of
here, so I made a new one and glued it back on.
And I flattened all these down a little bit
so now they're only about 3/4 as thick so hopefully they'll make less wind.
And next I'm gonna glue on the next ring on here.
I'm using my table saw to trim, what I've got so far, perfectly round.
I made a piece of plywood the shape of one of the
winglets and I just need to mark that 10 times
to cut all the pieces that I'll need.
Now I need to put these winglets on here
and I need to space 10 of those out evenly.
Now the problem is I should have done that
layout before I cut that hole in the middle.
'cause this is much more difficult now. I don't even have the center.
So I just measured that there is exactly 95 centimeters
around the circumference of the thing here.
So I'm just gonna attach the tape measure
here and
'cause I need to divide that circle into 10 pieces.
And now I know that every 9.5 centimeters I can put a mark on there.
So the first one is at 9.5. The next one is at 19.
Mark that one. And I just marked 19.
Now just push equal on the calculator
gets me to 28.5
I could do this in my head but I'd probably make a mistake.
Equals. Next one's 38.
So with the 2 layers of wings on this rotor now
it's quite heavy, so balancing it is very important.
So I've got a marble jammed in where the shaft is gonna go and
balanci8ng that.
Let's see. It's obviously heavy on this side.
If I put a piece of wood on here.
That looks like it just about balances it.
Which means that the amount of wood that I need to cut off from this side
is exactly about as much as here, so
I only mark here is where I'm going to have to drill out stuff.
So I end up drilling a bunch of holes along here
and it looks like its pretty balanced now.
It needs to be 'cause its gonna spin really fast.
So this rotor fits on the shaft a bit loose
so I made a shim out of a pop can
to line my hole with.
If I can get that on there.
It's always difficult to figure out if this is going to fit, ahead of time.
It seems to be going in
So I had a bit of excess shim that I ended up smashing with a mallet.
I put a v-notch in the wood and
gonna put this nail in here.
That'll act as a key way. And its in the keyway of the shaft and in the v-notch
so that prevents the shaft from spinning inside.
So for this test, I put the rotor on the floor
already. Just in case it falls off again.
And I'm gonna be at a safe distance. 'Cause I don't
know what's gonna happen when I power it up.
Ok. Here we go.
I had not anticipated that thing wandering the way it does.
Let's try that again.
And we're at 1100 watts, so that's a bit less than a motor.
But it should be ok.
Building this siren, I did a lot of work on the scroll saw
for cutting all these inside holes.
Here's cutting the hole in the front plate that's gonna be my stater.
I've got the first layer of my stater complete.
And the way this works, imagine this was a rotor
And it's got these little veins on it so
Let's just put down 2 of these to get you an idea, and it rotates.
And just like a blower, centrifugal force makes the air want to come out.
And so as long as I don't have theses things on the other side
the air just rushes out.
But if I do, then when it's like this, the air can come out
and then it can't, and then it can again.
And it can't.
And because I have the same number of these little winglets in here
as I have gaps on the equator here
that will cause pulsating air to come out all of these
which should give it a very loud note.
So here's my 6 gaps.
And these line up with the gaps behind here
So I have the rest of this thing, as it is, just clamped together
Is if the rotor hits the stater it will probably self-destruct
so I won't run up to full speed.
Oh, it's making a nice note already.
Now on the actual siren rotor, I've got 2 layers here
and this one has 10 whereas this one only has 6.
So, both of these together will produce 2 different pitches.
So I have to put another layer on the stater to have 10 of these
to correspond with the second layer.
Here's gluing the next layer.
Let's try it with the second layer of the stater.
That should add a higher pitched note to it.
And again, I'm just clamping this on temporarily.
Hopefully nothings going to self-destruct.
All right, second test.
Oh, siren-like already.
So it should get a lot louder once I spin it up to full speed
but just with clamps like that
I'm too afraid it's gonna wreck itself.
I got the motor running on a 2 x 8
and I've got these 2 brackets for holding
this part here.
And that's the outer ring.
And I have to make that so it lines up so that's in the middle.
So I'm gonna stick some spacers in here.
It should be bringing it front and middle.
Well, that should be the right thickness.
Might need another one.
And that looks like it is now in the middle
So I'm just gonna, for the time being, clamp that front face on here.
Making sure it's level.
And now pulling spacers out.
And that looks like it's got an even gap all around
and it doesn't hit.
So, I'm pretty happy with that alignment so I'm just gonna freehand
some drywall screws in here.
This is all very freehand.
Oh boy. I'm kinda afraid to plug it in
but here we go.
It works. It works.