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A spinning top made with a sea urchin shell

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Iacopo:

This is a decorative spinning top, very different from my usual ones.
I used the shell of a coelopleurus, a kind of sea urchin.
These shells, for their shape, dimensions and simmetry are suitable for making tops.  The protuberances in the shell are the joints for the spines, which the animal can move, for defense, and for slowly walking along the seabed. The shells can be brightly coloured, often with pink, red and violet stripes. The violet parts in the shell I used seem like painted, but they are not, it's their natural color.   

The shell is very light and thin, so I filled it with resin, mixed with metal powder, to make it more robust and heavy, so that it can act as a flywheel.
Since the simmetry of the shell is good, but not perfect, I had to balance the top, with the techniques explained in one of my old videos.  The wobble you see in the video is not unbalance, but precession.

I used boxwood for making the stem and the stand of the top; boxwood is very fine grained and hard, so it is suitable for making  fine, detailed turnings.  Some parts of the stem are very thin, (little more than 1 mm), so I inserted a 1mm steel rod reinforcement inside it, otherwise the stem would be far too weak for to spin the top.

Given the proportions of the top, tall and narrow, the relatively high contact point/center of mass distance, which makes for a high toppling down speed, and the rough surface of the shell, which makes for more air drag, this top doesn't spin for long;  usually it spins for 60-90 seconds, my best spin with it is 1'46".





I find sea urchins fascinating.  The following are two short videos about them, while it moves, and while it eats, (their teeth are a bit impressive):





I painted digitally the first picture in the video.  Here is a real photo of a Coelopleurus: 

https://fr.wikipedia.org/wiki/Coelopleurus_floridanus#/media/File:Coelopleurus_floridanus_NOAA.jpg

Jospin:
Very cool!

Iacopo:
Thank you, Jospin !

the Earl of Whirl:
You are amazing, Iacopo!!!

Yes, those teeth are impressive.....and kind of scary!

Jeremy McCreary:
Absolutely stunning, Iacopo! Getting 60-90 s of spin time out of this shell without appreciable wobble was no mean feat.

Now that you've joined me in the world of high-drag finger tops, can't wait to see what you come up with next!

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