Welding and Metalworking - millermatic 250 problem
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rkc1202
01-30-08, 09:56 PM
i have a millermatic 250 9 times out of 10 i begin to weld and when i pull the trigger instead of arching on the material it archs between the 2 rollers and melts the wire then it can't feed into the liner. when i do get it to weld the machine works great. as soon as i let go of the trigger and pull it again it arcs between the 2 rollers. i been messing with it for 2 weeks and i cannot find any problems. will someone please help me? thanks rick
MIGZICK
02-01-08, 07:42 PM
rkc1202,
I own a Lincoln 175 but there isn't a lot of difference between MIG welders in basic drive and electric circuit functions. What would normally occur when you are set up correctly to weld - work piece firmly grounded, etc. is that the contact between the opposite polarities of voltage ARC where the MIG wire touches the work piece, completing the electrical circuit. If a partial connection occurs along any part of the electrical circuit, you will have arcing at that point whenever there is a current demand. How much arcing depends on the voltage applied and available current. Enough of the technical stuff, though. I think you have 2 possibilities:
1 - Wire push problems at the wire feed to liner interface.
2 - An incompletely attached liner, right at the drive assembly.
Possibility #1
Check the drive/liner alignment. Make sure the wire can go strait into the liner, not cocked or off center. If this looks good, check the brittleness of your MIG wire. Mild steel MIG wire (not gassless/flux core) should be like string - you can tie it in knots. Gassless/flux core is somewhat less flexible and may break as you bend it at an angle. Make sure there isn't a pinch anywhere along the gun cable too - a crimped liner will cause feed problems, making the rollers work harder, resulting in a kink, etc. Check it out.
Possibility #2
My Lincoln has a separate screw that bears down on components that are electrically bonded to the liner, making it electrically one polarity (opposite polarity of your ground clamp). This also makes the rollers part of the circuit by virtue of being in contact with the MIG wire. If you're having welding at the rollers, check the mechanical connections of your liner and where your gun attaches to the machine and make sure the heavy power wires (the ones you switch to go from MIG to Flux core) are on their proper connection points. If all of that looks good and is correctly installed, check continuity from the roller assy to the gun tip with a multimeter (ohmmeter) in continuity mode (beeper). Work Safety Note: This is done, of course with the welder off, fully discharged and not a bad idea to unplug it too! If you have continuity there, then find a way to keep the meter connected on both ends (electronics & hobby outlets sell alligator jumpers that work well for this purpose) and wiggle the gun cable, listening for the beeper to silence. You must have full time connection regardless of movement. If the gun is installed correctly and you still have an intermittent connection, you may have a faulty gun assembly, broken components, etc? Hope this helps. BTW - if you don't have a multimeter - definately get one (recommend Fluke if you have the cash!).
MIGZICK
I own a Lincoln 175 but there isn't a lot of difference between MIG welders in basic drive and electric circuit functions. What would normally occur when you are set up correctly to weld - work piece firmly grounded, etc. is that the contact between the opposite polarities of voltage ARC where the MIG wire touches the work piece, completing the electrical circuit. If a partial connection occurs along any part of the electrical circuit, you will have arcing at that point whenever there is a current demand. How much arcing depends on the voltage applied and available current. Enough of the technical stuff, though. I think you have 2 possibilities:
1 - Wire push problems at the wire feed to liner interface.
2 - An incompletely attached liner, right at the drive assembly.
Possibility #1
Check the drive/liner alignment. Make sure the wire can go strait into the liner, not cocked or off center. If this looks good, check the brittleness of your MIG wire. Mild steel MIG wire (not gassless/flux core) should be like string - you can tie it in knots. Gassless/flux core is somewhat less flexible and may break as you bend it at an angle. Make sure there isn't a pinch anywhere along the gun cable too - a crimped liner will cause feed problems, making the rollers work harder, resulting in a kink, etc. Check it out.
Possibility #2
My Lincoln has a separate screw that bears down on components that are electrically bonded to the liner, making it electrically one polarity (opposite polarity of your ground clamp). This also makes the rollers part of the circuit by virtue of being in contact with the MIG wire. If you're having welding at the rollers, check the mechanical connections of your liner and where your gun attaches to the machine and make sure the heavy power wires (the ones you switch to go from MIG to Flux core) are on their proper connection points. If all of that looks good and is correctly installed, check continuity from the roller assy to the gun tip with a multimeter (ohmmeter) in continuity mode (beeper). Work Safety Note: This is done, of course with the welder off, fully discharged and not a bad idea to unplug it too! If you have continuity there, then find a way to keep the meter connected on both ends (electronics & hobby outlets sell alligator jumpers that work well for this purpose) and wiggle the gun cable, listening for the beeper to silence. You must have full time connection regardless of movement. If the gun is installed correctly and you still have an intermittent connection, you may have a faulty gun assembly, broken components, etc? Hope this helps. BTW - if you don't have a multimeter - definately get one (recommend Fluke if you have the cash!).
MIGZICK
rkc1202
02-02-08, 12:59 AM
Thanks for the info Ill let you know what happens ...Thanks Rick:)
lame_penguin
03-02-08, 02:42 PM
This is a problem I've never heard of before. Are you sure you're getting arcing at the rollers? Seems to me that one or two times of this would ruin them, I can't see them surviving it for two weeks.
If you *are* getting arcing at the rollers then most likely there's an intermittent ground condition taking place somewhere from the rollers back to the drive motor. It shouldn't be a case of intermittent failure in the power supply to the tip because that circuit should only go to the tip, there should be no point where it reaches the rollers before the tip.
Be sure you're not getting a case of the wire sticking to the tip. That's about the most common problem with a MIG. If your gun uses Tweco tips it's pretty likely. Tweco tips are pretty cheap, it's common to get several that make trouble before hitting a good one.
If you *are* getting arcing at the rollers then most likely there's an intermittent ground condition taking place somewhere from the rollers back to the drive motor. It shouldn't be a case of intermittent failure in the power supply to the tip because that circuit should only go to the tip, there should be no point where it reaches the rollers before the tip.
Be sure you're not getting a case of the wire sticking to the tip. That's about the most common problem with a MIG. If your gun uses Tweco tips it's pretty likely. Tweco tips are pretty cheap, it's common to get several that make trouble before hitting a good one.