I designed this unit off a modular shelf unit I saw some time ago. I used gears instead of tubes and designed 3 possible shelf sizes to fit however is needed into the gears. Each gear can be added or removed separably for reconfiguration of the unit. The units are 1 foot in depth and internal diameter but could be any size, even mixed sizes, because they are gears, they can be fitted more solidly than tubes. You could do the gears out of metal and the shelves in wood or reverse.
Art's Folly 
Functionally it works as shelves.
However, gears that look as if they cannot rotate niggle at me.
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If not attached, they should be able to actually. That is actually part of why the shelves are not all the same direction. Both because they can be put where needed and the shelves can turn anyway. It would take some work to design a system that would turn them without your input.
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They looked interlocked to me; if they are designed to rotate that is great.
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One probably could not rotate without all of them rotating unless I altered a few things, but there is no reason they couldn’t. That is why I angled the teeth actually, if they are not angled then there is only one spot they fit together. Because each unit is made separately, the choice to lock them together or simply mesh the teeth is one of instillation.
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