I had posted my efforts on Outdoor Magic and got an interesting idea from Captain Paranoia regarding separating the airflow to the main burner from the airflow to the upper vents in the firebox. I had a vague idea of how I could modify my design to incorporate Captain's ideas so spent another day in the garage/workshop trying it out.
I made my Firebox as before, cutting off the base, shortening the can and pressing the base back on. For the outer part I needed 2 x 1250g cans. I used 2 cans so that I would have a top and bottom with no holes allowing me to cut out a hole in each to fit the firebox. I cut the smooth section with the lip (the actual top of the can) off one can and then shortened it to about 10mm less than the height of the firebox. The top smooth section with the lip I kept to use as the base. I then cut the base off the second can and pressed it onto the open end of the can I was using for the outer. I then cut a hole in the top and bottom to allow me to press the firebox into place. Once the holes for the firebox were cut and prior to pressing in the firebox I drilled a series of holes to feed air to the firebox upper vents/Jets, that done the firebox was pressed into place. The base section that I had previously removed and kept was then drilled to supply air to the base/grate of the firebox, as this section had the rim the main unit stacked securely on top.
One other aspect of Captain Paranoia's design was to have two rings with holes matching both the base intake holes and the secondary vents holes, these would rotate and allowing the air supply to be adjusted offering control of the airflow to both grate and upper vents independantly. I haven't got around to that yet but it shouldn't be too difficult.
The pic's below should help make the build clearer.
Left, base to be pressed onto outer can, right, section to use as base. Both cut from one can.
Firebox slightly taller than outer can, outer can with base from other can pressed on, both ends cut for Firebox.
Firebox pressed into place.
The secondary air supply is now isolated from main burner/grate air supply.
Main Section (Outer/Firebox) seated on base (Rimmed section cut from top of other can) Mesh potstand simply rests on the top held in place by the edge of the can.
Stove set up to operate, the pot is a Stainless Steel one from a set of 3 I bought today, £3.99 for the set from B&M.
The stove fits the pot nicely.