Summary

The classic wooden multi-tone Train Whistle you can now print (I would love to see this printed in wood).

Instructions

You will need some sort of glue for this one as I could not think of a way, due to its design, that it would work very well any other way.
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I added the ears/tabs as a way for you to slide one over the other where both flat pieces will be glued, and clamped, together.
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The body will need sandpaper on the side with the tabs (the flat part) as I originally had each piece laying flat on the glass but with the need of glue I added the tabs to help people place them together properly so I had to turn it around 180 degrees which leaves a need to smooth the top so both pieces go together well.

Classic Train Whistle with Solidworks 2014 source