Not so much the weight you have to worry about Ade, it's the balance.
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For a brake drum you could work out the rotational RPM at say 100 MPH and then spin the thing equivalent of say 150 with safety. As long as the drum is in good Nick to start with and balanced, you should have no problems.
Balance - agreed... and I have no way to balance it other than statically, which is almost certainly not good enough... However.. my unit will be nowhere near 25l in capacity; that must have been a bloody monster of a machine!
I reckon the capacity of my brake drum, by the time you've added the centre spigot & lid, will be around 1.5-2 litres tops. It's about a foot/30cm across, if I recall correctly, and about 5"/12cm deep. I'd like to spin it as fast as humanly possible...
Assuming it used to live inside a 13" wheel (which seems about right, given its age), that would have had a 4 or 5" sidewall tyre fitted, so about 23" total rotational size, which is about 72" circumference (handy), or 6ft.
100mph is 8,800ft/min, so the brake drum is doing 1470rpm just about. So your safety margin gives me 2200rpm. I was hoping for at least 3600, and maybe even higher...
Next up - work out how many g's that is. That's beyond me tonight... I'll have a go tomorrow.
Anyway, as I wouldn't trust it not to explode at very high speeds, I intend to wrap it in a 5mm thick steel enclosure. I guess I should be able to calculate the centrifugal forces on the side of the bowl at a given RPM, then assume a 1lb lump flies off I can calculate the energy in that when it strikes the outer casing, which will tell me if I need to put a second 5mm steel ring around the inner one for protection purposes... although I might just do that anyway. Steel is a LOT cheaper than internal organs, and a damn site easier to replace...
