I started off with a stainless steel, double-walled ice bucket from a thrift store. The size is between a 1 quart paint can and a small coffee can.
14 holes at the base of the outer wall, each aligned with a ¼" hole in the firebucket. After hacking off the bottom of the outer layer, I cut a bunch of slots in the floor of the firebucket with an angle grinder.
Since I couldn't remove the firebucket to drill vent holes in the top, I used a cut-off wheel on a Dremel to cut rows of slots instead. 3 rings of staggered slots, 6 slots in each ring.
Stacked pencil-sized twigs in vertically, and top-lit it with a wad of drier lint and a few more twigs. Observations:
- I understand now what is meant by a 'smokeless' burn. There will always be a little smoke of course, but far less than an open fire, and mostly when new fuel is being added to the fire and is lit from below.
- At first I thought flames were just climbing up the walls of the firebucket, but on closer examination, it really did look like there were flames starting at the vents at the top. That's what's supposed to happen, isn't it? I was very excited to see that!
- After 10 to 15 minutes of feeding twigs into the fire, the ash pile was no more than ¼ of a cup of fine powder, with only 1 or 2 pieces of charred wood about the size of a pencil eraser.