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SCUBA tank bell

Picture of SCUBA tank bell
I was at an event  recently where someone had the most amazing array of instruments made from recycled stuff.  The one that really captivated me was a hanging set of gas tanks that had been turned into bells, though I suppose you could call them a tuning fork (though they may not be in tune) or a gong.

Essentially a line is cut across the bottom of a gas cylinder continued about 300mm (since imperial people rarely include metric measurements, here it is back at ya) up the sides with the cut being on opposite sides on the way up.

This splits the lower end of the cylinder into two and when given a decent hit with a striker of some sort (wood is best), will ring loud and long and if made with care, in tune.

Since I had a well out of date SCUBA tank lying around I thought it absolutely vital I made one of these and at the same time, my first instructable - please forgive phone camera.

What you need:

An empty gas cylinder - scuba, oxygen etc.  This may work with a round tank but I have only done it with a long cylyndrical one.
Angle grinder and a few 2.5mm cutting discs 
Maybe a hacksaw (with a spare blade)
Dressmaker's tape measure  or builders tape measure and a piece of string
A marking pen
2 saw stools (to use as a jig)
Spirit level (if your work space is a bit uneven)
Chalk line (optional)
Other stuff 


I just noticed something about the video.  When the tank is spun rather than going wow - wow - wow, every time a cut passes, it goes wow wow - wow wow - wow wow  one wow as the cut approaches the front and one as it departs the front, reinforcing the idea that the wow doesn't happen when the cut is right in front of me.  There must be an explanation for this.

 A couple of words of caution that should be obvious, but here they are anyway:  Make sure there is no pressure in the tank you are going to use - open the valve, leave it open, maybe even remove it.  Also, if the tank has been used for any sort of flammable gas, release any pressure, remove the valve and fill it with water (then empty it) before cutting.
 
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You should look up propane tank hang drums (or Hank drums) on Youtube. They are a different type design where...tabs, I guess is the best word, are cut into an old propane tank and vibrate when hit with mallets or a hand. They're similar to xylophones and the like in that respect - stiff surfaces connected at one end (embedded cantilever-type). You might enjoy making one, and there are lots of fantastic instructions online - I think it would nicely complement this tank instrument.

This is a very cool build, by the way. If I ever come across an old scuba tank, I'd like to build one. My folks' garden is filled with windchimes and gong-type instruments - I've always loved these types of things.
rimar20003 years ago
This is wonderful!

Many (many!) years ago I read that aluminum is the most sonorous metal. At first I can't believe it, but as I had a broken Al bicicle ring (almost a circle, open 10 cm on the break), I did a try: hung it from a branch of a tree by its middle, and hit it with a stick. The sound was very, very strong! After this I thought the alum pans/pots are very noisy, and I think it is truly: Aluminum is the most sonorous metal. But a search in Google today says nothing about the matter.

Maybe you know that better than me, ¿is it so?
My thoughts are that the cut is not to let the sound out but to let what is left vibrate more freely. Or in other words, the sound is not coming from the cut out section but from the vibrations made by the outside surface of the tank

Without any knowledge of acoustics or engineering I am really only guessing when I suggest the the metal near the cut would be vibrating more than the metal in the centre of each curve.

Is there an engineer type of person out there who can confirm, deny or expand on this? If you confirm my theory as correct I will feel very clever. If you show how wrong I am I will be almost as happy to be learning something new.
Microbe (author)  waynevanwijk3 years ago
likely. Maybe widening the gap gave it a bit more space to vibrate, though I think I would have heard it buzzing had the two sides been touching.
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