I assembled an atmospheric injector burner loosely based on Michael Porter's design using plumbing parts and a .035" MIG tip. When you figure my time, buying miscellaneous hardware like small taps and drill bits, multiple trips to several area hardware stores and ordering the schedule-80 1/8" pipe nipple, I'm not sure it's more economical than buying a precision-made burner like those from Rex Price or Steve Gensheimer but it works (and I learned a bit). The flame is very stable and it easily brings a 1/2" square bar to a light-red heat. I can't wait to build the forge.
!http://www.lonsteins.com/blog/images/33.jpg (burner body)!
!http://www.lonsteins.com/blog/images/34.jpg (burner gas feed)!
!http://www.lonsteins.com/blog/images/35.jpg (burner operation)!
!http://www.lonsteins.com/blog/images/36.jpg (burner with hot steel)!