I have a soldering iron type with a feed tube and an air welder, I prefer the "soldering iron" because i can smooth out the surface of the two pieces with the tip of it, less sanding involved. The air gun pretty much just melts the pieces so you can paste them together, you can use rods with both, but the speed tip (soldering iron) works best because it is more precise... If you combine the speed tip with a standard heat gun it is possible to mold the ABS into what ever shape you desire... A good way to make parts i have found is by fabricating a solid structure out of plaster or wood, then heating up the ABS with a heat gun allowing it to form over your solid structure, then using the speed tip to correct imperfections and piece it together. Make sense at all? Hope i could help.