Miller MIG question

I'm helping a friend who's having problems with his Miller MIG, a 172, IIRC. A 220 wirefeed running .035 wire and CO2. The machine will click, but not push out wire. You have to click it several times to get wire to advance, then the arc is sometimes sputtering like the wirespeed is varying. At other times, there is no click, and no wire advance. The outcoming wire has indentations from the drive rollers, and I even backed down on the tension thinking it may be causing burrs that are dragging on the liner. When I clicked it on, I was pulling the wire with some pliers thinking I'd see if it was dragging in the liner, but it was stuck tight and not coming off the reel at all. I did not check to see if the wire was energized on the times it would only click, or not click. Anyone have this problem with this machine? Help, advice, solutions, opinions welcome.

Steve

I suspect from the way it was running when we shut it off that it will go to a service center soon, and I will report the findings. Right now, I'm just trying to get ideas to take back Monday to make suggestions on what he might try or check just in case we've missed something simple or obvious. The boss is retired ex military who used to build and run radar systems for the AF, so some DIY electricital repairs are not out of the question.

In the meantime, I'll take my Lincoln 175 Plus over there to finish the job. This Miller has been used a lot to make ornamental metal, and is probably just in need of a full service call. Too bad they don't last forever. I did have a MillerMatic that was shop used for eight years, and I never even had to change the contactor points. Some are just built better than others, and some have more frequent service intervals.

Steve

1. Call the service shop and ask them what the top 3 causes for this behavior are from their experience.
2. Make a checklist for each area involved:

- supply spool: is there an anti-backlash brake that might be sticking

- tension mechanism: is it even or erratic; take the wire out of it and see what it does

- drive motor: does it run smoothly without a load

- cable body: is there a permanent kink somewhere; has dirt accumulated

It should be possible to cut the wire just before the feed rollers and use that piece of wire to manually test the whole mechanism - a

Try swapping out the gun liner. They cost about $10 and all your problems sound like classic dirty liner syndrome.

The liner is a steel spring inside the gun feeder that guides the steel wire to the gun. As you weld, small flakes of copper plating and bits of steel wear off of the wire, and eventually clog the liner, causing feed problems.

I had the exact symptoms recently on a Miller Matic 35.

Turned out to be a small double pole relay. One pole switches the wire feed motor on, the other supplies currently to the contactor coil. Although the switch was no longer available for my specific machine, it was easy to find one locally that would suffice.

Might also be your trigger switch too.

Try swapping out the gun liner. They cost about $10 and all your problems sound like classic dirty liner syndrome.

The liner is a steel spring inside the gun feeder that guides the steel wire to the gun. As you weld, small flakes of copper plating and bits of steel wear off of the wire, and eventually clog the liner, causing feed problems.

I tend NOT to think it's the liner because:

at times, it does not click when the trigger is pulled. at those times, the tip is not energized. at that time, one cannot pull out wire with pliers. when I get a click, and am pulling on the wire at the same time, it will not come out, and it it was bound, I'd be able to bring even a little out by the pulling. when it does weld, sometimes it runs just great, and if it had a sticky liner, it would run slow all the time. when it does run, the speed seems intermittent because the behavior of the transfer process changes from hissssssssss to splut, splut, splut.

Anyway, as I say, the Lincoln goes to the rescue tomorrow, and the Miller will probably go to the shop soon. The guy is leaving for Cal from Utah in a week or so, so may take it there with him, or to the shop in Vegas where all St. George work is sent anyway.

Steve