That is one excellent idea that i applause, and as a matter of fact, this is the correct way of recycling! This type of machine is not original, but the use of it, is. Such machines are used by the tube manufacturers. They make a groove near the edge of the tube, so that the tubes do not bend. But calischs did this for another reason. First of all, he did the groove near the bottom of the can. This way, the diameter at the bottom is reduced, and it can be inserted into another can laying under. The groove is made with a pair of round pins, one of which is manually rotating. Awesome idea!
These are the round pins used to make the groove:
This is how the cans are stacked one above the other:
Watch the following video to see how the groove is made: