I decided to construct a small portable forge to be able to work at home or away from the workshop. Its built out of an Illy coffee can, diameter 20cm, length 30cm. Lined with 5cm of refractory blanket.
I also tried to make a smaller propane burner, instead of the 3/4 inch Zoeller sidearm burner I use on my larger forge. This one is made out of 1/2 inch pipe, with a 0.6mm gas tip. I had some trouble making the air inlets without a drill press, and I will probably have to go to a machinist to drill them properly, but for testing they suffice. The rules of thumb for such a burner are a length at least 9 times the diameter of the pipe, a flare at the end, and an air inlet area equivalent to the opening of a 1 inch pipe.
After some tweaking here is a first acceptable flame. The good thing is that this type of burner runs well even on very low gas pressure. Also the 0.6mm tip used instead of the 1mm for the 3/4" sidearm burner should keep gas consumption to about 1/3 of the larger burner, which will mean much lower running costs. I should also built a sleeve around the air inlets to be able to control air intake and oxidizing-reducing burn.
On a first test the forge went up to 920C in 1-2 minutes, but I still have some doubts as to how well the forge will handle such heat. More testing will be posted shortly...