LTD Stirling Engine
I am noodling with an LTD Stirling engine. I have wanted to build one for a while, and it may work in as a project for K-12 students. I am creating this page to post some notes as I go through.
First Parts Picture
So far I have made the power piston, cut down two large tuna cans and a standard 2 liter, and made a displacer piston.
The power piston (little orange thing on the lower right) is a diaphragm type using a gatorade bottle lid, 1/4-20 x 1" machine screw and nut, two 1 1/4" dia fender washers, a punching balloon, and two rubber bands just the right size to go around once. The gap between the fender washers and the wall seems pretty ideal. Wide enough to give a decent stroke without stretching when tight or wrinkling in mid stroke, but small enough that it should keep power loss reasonable.
Large tuna cans and a standard 2 liter are just the right size for each other. I used a side-cutting can opener -- the weird ones that don't leave a sharp edge -- and I think I'm going to be able to get both cylinder heads out of a single can.
I used the dumb-guy method of cutting the displacer out of a leftover piece of polystyrene packing material; cut a smooth edge on one of the tuna can walls and press it through cold. I think heating the can with a torch to hot-cut the foam would be worth the effort, but the cold method worked well enough for the first draft. To get the billet out of the tin can, I just lightly heated the sides of the can to shrink the polystyrene a bit. I then ran a low flame around the circumference to shrink and harden the edges a bit more, testing the fit in the tuna can as I went (it should fall under its own weight when you drop it in).
Random Thoughts
Cut Sheet Steel Is Sharp
Cut sheet steel is sharp. Little slivers of cut sheet steel are sharp and nearly invisible.
When cutting tuna cans with tin snips, if you back the snips out of the cut by even a little bit, or don't keep them tight against the end of the cut when opening the handles for the next snip, it is really easy to catch a hair of metal on one side of the existing cut -- which will create one of those sharp, nearly invisible slivers.
Therefore, if you maintain constant gentle pressure holding the snips against the end of the cut, you reduce your chance of getting an annoying metal sliver in your hand.
Gloves probably would have helped too. :)
Solid White Albacore Is Better
I got one can of chunk light tuna and one can of solid white albacore so I could do a shootout. The chunk light tuna is OK, but I think the solid white albacore is worth the 50% markup.
After writing the previous paragraph, I decided I wanted to check the state of commercial tuna fishing. Wikipeda: Tuna has good info. Bluefin tuna, the most prized, may already be collapsing. Albacore and some of the other relatively rare species are on the Greenpeace "red list," meaning they think those species are in trouble. Skipjack, which makes up most "light tuna" and other can and envelope tuna in the US, is not considered as being over-fished.
Just providing the info, of course -- not saying if or how it should affect your tuna budget.