Tumbler Stable Kiln: Open Design Disclosure for an Open-Top Flame-Cap Biochar Kiln

The Tumbler is an open-top flame-cap kiln for making biochar. Its frame is a pear-shaped hexagonal prism, the shape commonly called a hopper. Each end is a hexagon with a flat bottom edge, two lower facets at 35° and two upper facets at 70° from horizontal. The kiln rests upright on its flat bottom and can be rolled onto a facet to load, tend and dump the charge; frame members act as the stops. The kiln has no hood, no cover and no moving parts. The sheet-metal walls hang from the frame and carry no load. This disclosure gives the idealized geometry, a member list for a welded frame, and a bend-and-bolt version built from 3/4" EMT conduit with no welding, plus dimensions, materials, a cut list and variations. It is published to place the design in the public record and to make it free for anyone to build, use and change, under CC BY-SA 4.0.