Click on drawings to download - for personal use only.
CHIMNEY
The main chimney is a simple job from 10mm OD aluminium tube, thread one end M10x1.0 for a length of 22mm. Face to length and form the 9mm dia spigot on the other end. I used slightly larger OD tube so had to machine it down to overall diameter.
The base is just some 12mm stock drilled to 9.0mm and tapped M10x1.0 with the upper edge rounded off.
The top ring can be turned on the end of some bar and if you put a parting cut part way through so the bead can be easily shaped, the drill will part off the work as it breaks through.
The parts can be assembled with a drop of Loctite 648 to hold the ring in place, make sure you have no more than 2mm of thread sticking out the bottom otherwise the exhaust passage in the base will be restricted.
And a quick test fit.