well since others have revived this thread I may as well comment too... aside from the obvious safety issues with most can crushers, I haven't made one so far because it has not been worth the effort, at least yet.
Toronto recently approved drinking in public parks. Previously we had drinking in public parks on a fairly wide scale anyway but on the down low. Evidence was taken away by industrious people collecting huge bag loads of cans to return to the liquor stores.
I have often watched an elderly couple in one park hauling huge bags and thought why the hell don't they use a cart and a can crusher? Likely renders the cans unreturnable for deposit....
I'm basically too poor to be able to buy aluminum for casting, so I keep thinking about the opportunity to collect cans during festivals and long weekends in order to get free aluminum.
IIRC it takes between 55 - 75 aluminum cans to make up 1 kg of aluminum. In order to be worthwhile for me I'd have to collect enough to make the equivalent of $25 / hr. At a scrap price of $1.25 / kg of aluminum cans I'd need to collect and crush 1200 or so cans per hour.
It would take about 6000 cans to obtain 100 kg of aluminum. How large an air pig would I need to bring to run a crusher? Too big...
That would definitely need to be a drinking event too...
So still not worth the effort.