12 half-inch holes around the bottom of the coffee can, 24 quarter-inch holes around the top of the soup can, and the bottom of the soup can is perfed with as many quarter-inch holes as I could fit without violating the integrity.
The only trick is in cutting a hole the size of the smaller can in the top of the coffee can, instead of removing it with a can opener. The inner can then will friction fit quite tightly.
It burned like a champ from the get-go.
The photos are in reverse order, but the daylight photo shows it just top fed to burn off the interior coatings, while the top one shows it in action. You build up a snug bed of smallwood right up to within an inch or so if the top. Then you light your fire on top of that, and it will burn down through the pyrefication levels below. As it comes up to heat, the volatile gases are pulled down through the pyre, and then rise up the space between the two can walls where they ignite. This gives you an incredibly hot, incredibly efficient burn. Once it is going it is almost smokeless.
I understand that you can even fire it with wood stove pellets. I'm going to have to get a bag full of those from my buddy and try it out. I am also going to keep my eye out for one of those piles of wood chips along the roadside that get left behind by the tree trimming crews. Dry those out in the sun nicely, and I'll bet they would work just as well. Free fuel is good fuel. "Leave No Trace"...
I have to build a "set off" ring from a cat food can to go on top and provide ventilation between the fire and the cooking pot. Once I get it going for real, I'll post more photos, and give you a time-up-to-boil. I may be able to give this a workout next week. There's a pretty fair possibility that my buddy and I will be taking a hike up along the AT, and if we do, I will take this long.
It looks like you should be able to just toss a second coffee can on top as a deep boiler. A couple of MREs ought to fit nicely.
