On Sat, 20 Aug 2005 11:51:22 +0000, habbi wrote:

What is the advantage of having the spool at the gun, why not just have the
drive system in the gun and leave the spool at the machine. I guess one
reason would be if your gun was far away from the machine. But I am
referring to a 10-15' gun. It would make a small 175 amp mig machine ideal
for small aluminums jobs. I might try this on my Lincoln sp-170.

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.