spool guns

Spool guns are mainly for aluminum wire because it doesn't feed well through a long feed tube. Has a nasty habit of kinking and getting bound up.

Some MIG welders do have the drive mechanism in the gun and keep the spool in the machine. IIRC, this is called pull feeding. In fact I think there are push-pull feed systems as well, with drives in both ends of the torch cable. I believe that even with the wire being pulled through the liner it is still prone to binding if the torch cable becomes looped, etc. Any changes in feed rate can raise hell with a weld's quality and can make keeping an arc established difficult as well. Spool guns solve this problem by providing a short straight path for the soft, easily kinked and galled aluminum wire to travel in. The real downside to spool guns is their ridiculous expense! I guess part of the expense is because spool guns must be kept light in order to reduce operator fatigue, and the entire mechanism, including the spool housing must be kept air tight, thereby complicating the design.

Aluminum wire is too soft to be pushed through a long gun lead. What I understand happens is, you get birdsnesting a lot. Google on it. - GWE

As Artemia says,some guns do have the drive in the gun and the spool at the machine.Esab had plants for aluminium thirty years ago that had apull drive in the gun and a speed control drive at the machine.IIRC they were feeding aluminium wire a hundred feet,mainly used in shipbuilding. regards,Mark.