> Kevin, I found what worked best was to form the vanes into the chimney itself. This has the advantage of increasing the surface area in contact with the water.
LOL! I obviously didn't make myself clear; that's exactly what I did, but my thinking was also that it would be much better heat transfer (simple press fit gives poor thermal contact), and it would ensure that the can wall (and epoxy) never got hotter than 100C.
This is a great example of congruent design; we've both approached the same problem, and come up with an identical solution, even, coincidentally, using the same brand of beer can, although I suspect yours is one of the big 24oz cans, whereas mine is a small 440ml can. There are a couple of other minor differences; I cut a hole in the dimple, which makes the top of the inner stable (but makes filling a little difficult), and I used an odd number of vanes, as this seemed to improve the useful cross-section area of the top opening.
> Maybe it wouldn't be prudent to give all my secrets away, especially given the Bush Buddy/ Bush Cooker debacle.
That was an unpleasant and unnecessary debacle, IMHO. On the thread, I argued the case for congruent design, and lo, Roger and I have given a perfect example of the phenomenon. No doubt bpl's worthies will be along later to shout "RIPOFF!"... I can look back and see how the idea came about, given the past history of things I've experimented with, and I bet Roger can do the same. No doubt the design history is different (and collides a little where Roger's aluminium water bottle kettle gave me a prod to play with some ideas I scribbled on heat exchanger pans when I got a JetBoil), but the end result is remarkably similar. We even made the same error of folding the wall the wrong way so that the paint is the water side, rather than the epoxy-phenolic coating (corrected in the earlier photos)!
OM Bush Buddy Ultra thread
OM How To Make Meths Stoves Q&A thread