zondag 7 juni 2015

Air raid sirens / speakers: a tutorial

You go old school, of course.

Remeber these from yesterday?





Bear with me then :) While working on my minaret 2 years ago I thought it would be cool to have some speakers on the sides. I then looked around for speakers and found none. I have now restarted the buildingsproject and dammit, I want those speakers. Not only are they great for the minaret, but they work as air raid sirens too. You know, these:




Since 3D printing is all the rage, I looked at that. But that costs a lot of money. Which I don't have. What I do have is time and the ability to see things in 3D in my head and break them down in parts, so I went with that. These kind of speakers have a very basic shape that is easy to copy, so I cut up and laminated some flat bits of plasticcard, cut away the excess plastic and sanded it smooth. Basic shape done (top picture, red shape on the right). I then took my trusted Oyumaru moulding clay and made 4 moulds of the basic shape. Job done. For the inside shape I repeated the process but made sure the diameter was smaller then the shape I just moulded, drilled it and glued a handle in it. (Top picture, left shape). Now I was set to test this (it's one thing to make up things in my head, another to make it really work), so did a test cast with greenstuff.

Not perfect but the theory was sound. I let these dry and popped them out this morning to see if it worked ok, no too thin walls or anything. I cleaned one up and removed the excess greenstuff, sanded it down a bit and drilled a hole through the back. I then inserted my last clothing pin. glued it in place and bent it in the back.



 Et voila! A speaker/air raid siren. It really is that simple. It is not perfect but looks the part, even more so when painted a bit battered.

I then spent the day moving bricks out of my garden to the street and pondering on how to improve this. The greenstuff gives it a bit of flex, and I wanted something tougher. I read about using Milliput with Oyumare and the warning that comes with it (it leaves a residue) but thought what the hell. I also wanted to decrese the time used per siren.

So here goes :)

-Make master shape and indentation tool, sand them smooth.

-Make moulds of the master shape (in this case 4 as I wanted to copy the 4 horn version)

-Mix up a small ball of Milliput. Press into the mould and use a wetted knife to remove the excess

 
-Wet the indenation tool, and press down, causing excess Milliput to spill from the sides. Don't press down down all the way at once, you will get the tool stuck and rip out the entire piece. Better to press down a bit, remove, wet again, press down again, remove, wet again, and press down again
 
-Remove the tool, it should look like this:
 
-Take the wet knife again and remove the excess Milliput.

 
-I then wet the indentation tool again, and press down again if the shape is a little bit off centered. This step doesn't matter too much though.

-Wet your finger and smooth out the edges, feathering them towards the outside for a smooth transition.
 
-Fill your moulds and repeat the steps.
 
-I let these dry for about 8 hours and then popped the moulds. If you mixed the stuff 50-50 they should be hard enough now. 

The inside of the moulds was clean, the outside not, though most just broke off. This means you have to cut away some of the Oyumaru and throw it out before reusing the plastic. Seeing as these moulds will be used for some time to come, that is no problem for me.

-Sand what excess Milliput remains, drill a hole and insert a clothes pin, or keep as is and only drill a hole in the back for mounting it to a wall, or a pole.

That's all there is to it folks. I will be using the same technique to create hollow dragons teeth as I want to have at least 2 metres of them, and hollow casting makes me last my Milliput so much longer. Sure, it takes a bit longer to cast them all up, but seeing as I was quoted over 80 euros in teeth and shipping for 2 metres worth, and Milliput extra fine (which I prefer) sets me back 7,45 euros per pack and lets me create a lot of teeth, it is the way to go. With 10 or more little moulds I should have enough teeth cast in a month or so, and it only takes a little bit of time each night. Actually, I can cast them early in the evening, get up 15 minutes earlier, cast another set in nthe morning, and pop those in the evening, doubling my speed.

I hope you found this useful, and might help you tackle one of these projects yourself. It is not hard to do, it just takes time and can get a bit messy.


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