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MM 250X - difficulty starting arc

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  • prostreetboy
    replied
    PJS,

    Thanks for the feedback. It looks like the run-in adjustment has really helped. It's not perfect yet, but at least I can get the arc started about 70% of the time. The adjustment to the R65 pot was factory set to 5 o'clock, I moved it to about 4 o'clock. We'll see how it continues to go.

    Dave

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  • Paul Seaman
    replied
    prostreetboy: When I was brand new to mig a few years ago I ran into a similar problem, it was a bit of dirt in the screen on my regulator sometimes it would feed gas sometimes it just wouldn't it cost about $60 to fix not a problem after that. Just another idea if all else fails.

    ps my supplier will check regulators for a nominal charge, I think $15, peace of mind vs cash. Good luck and weld well

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  • prostreetboy
    replied
    Lee,

    I just got off the phone with Miller. The MM250X is set up to run .035 wire because that's a majority of what people use. He knew exactly what I was referring to regarding the burnback of .023 wire and said the run-in pot adjustment is the first thing to try. I didn't realize the run-in circuit is activated until an arc is struck. I assumed it was more time dependent with a fixed ramp. The R65 pot essentially adjusts the speed of the wire to some % of the front panel setting prior to starting the arc.

    He also mentioned that if a lot of tacks are being done in succession, then there is a diode (D1) that I could try snipping which controls a hot start feature. Apparently, repeated tacks will not allow the circuit to fully discharge and the starting voltage will ramp way beyond what's expected.

    I was playing with the pot last night and am starting to get better results. I'll keep you informed.

    Dave

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  • lmaini
    replied
    Prostreet - I adjusted the pot to speed up the runin. I used the old trial and error method. I would move it, try some tacks, adjust it try some tacks. I continued untill I was happy with the performance. A word of caution use the smallest screw driver you can and don`t go nuts, as there is only 270 deg. of adjustment on the pots. To far and you got big trouble.

    As far as I know, there is an upgrade available - It is called the MM251.

    Good luck and let me know how you make out. - Lee

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  • prostreetboy
    replied
    Lee,

    I hope you're right, I can't wait to try it. One question...it's not clear to me if the adjustment you made was to slow the wire down or speed it up, I'm assuming speeding up is the right direction but wanted to confirm with you first.

    Did you do any further research about "upgrading" to an externally adjustable run-in?

    Dave

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  • lmaini
    replied
    I feel your pain

    Prostreet -

    I know exactlly where you are coming from. I have the same machine and have had the same problem. It results from incorrectly adjusted run-in. If you research this, it is something Miller knows about and has fixed in the MM251, which has externally adjustable run in.

    Please see my post on the hobart board:

    http://hobartwelders.com/mboard/show...highlight=250x

    This post will give you the cause, the correction and the people at Miller to call for tech assistance.

    I applied this adjustment to my machine and have all but eliminated the burn back issues.

    Good Luck - Lee

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  • prostreetboy
    replied
    Hey Nunzio1,

    I actually do have a Miller machine, it's a 250X, about 2 years old. Still looks like it came out of the crate. Thanks again for the thoughts, I'm filling up the gas tank tomorrow for a full weekend of welding.

    Dave

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  • Nunzio1
    replied
    Dave - Next time you watch American Chopper look around the shop - they use Miller welding machines exclusively- if you ever have the opertunity to use one,instead of a Hobart or Lincoln, I think your problems will go away...in the mean time get some sheet metal the same thickness as is on your pro street 37 Chevy and practice on that while trying different wire feeds and slightly higher voltage settings. Start with what is recomended on the chart on the machine, but play around a little - it is also helpful to have an assistant vary the wire speed slowly as you are welding untill you can get that "sizzle "sound. One other thought is I use isopropanol alcohol as a degreaser in a squirt bottle on the metal prior to welding and blow it dry with compressed air to insure that the weld area is clean. Caution - the isopropanol alcohol is highly flammable - so proper ventilation is necessary. Another thought - any little residual grinding dust left in the seam of the metal will make welding more difficult. If all of these hints do not work - your welding machine is not feeding the wire at a consistant rate and perhaps the wire feed mechanism is faulty - you should be able to adjust the wire feed so that if you feed the wire from the end of the gun against a wooden 2x4, it should push your hand back with considerable force.

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  • prostreetboy
    replied
    Andy and Nunzio1,

    Again, thanks for taking the time. Here are some of the specifics of what was happening a few days ago even though it's happened routinely since I've owned the unit.

    I'm welding on 16-18 gauge sheetmetal using .023 wire. I'm not sure of the exact alloy, but it's what the local welding shop recommended for general auto use (either ER70S-3 or ER70S-6).

    Gas flow is set to ~20, rollers and contact tips are all sized for .023 wire. I do know that I've been running the roller pressure lighter than recommended, so I plan to bump that up. I've tried stickout form 1/4" to 1/2"+. It does seem the shorter the better. It also seems to happen for frequently the more perpendicular the gun is to the material.

    When stitching this particular panel in, I probably placed 30-35 spots over a period of 1/2 hour to try and minimize warpage. I have tried snipping the end of the wire each time to eliminate the ball. My sense is that the popping and sticking to the contact tip is reduced but not eliminated. What I did notice is that when I finish a stitch and go immediately to another one when the mig wire is still red, it usually doesn't pop. Some tacks go perfect, so go so-so and most pop and spit, all within a couple of inches of each other.

    Also, if it does start to pop and not sizzle, if I stick with it, it generally seems to settle in to a normal weld pattern (now with lots of spatter and higher bead than I was hoping for.) I was just watching American Chopper when every tack they did started immediately with a nice sizzle...how the little things in life could make me happy....

    The last observation: wire feed rate and voltage are set per the chart on the inside of the cover (+/-10%). I noticed yesterday that immediately after stopping a weld, the set voltage has dropped on the machine (maybe by a volt or so). I imagine it's the in-use number that should be set to the chart???

    Thanks again for putting up with the questions....

    Dave

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  • ASKANDY
    replied
    Prostreet,

    What size wire and thickness base material? Something that a bunch of our body fabricators do while doing tons of tacks is to clip the ball off the wire each time before starting. Some brands of wire tend to ball up more while others seem to run well all the time.
    Also, make sure your wire size is not larger than the base metal and that you have the correct liner and tips in the gun.

    Welcome aboard.

    Andy

    Leave a comment:


  • Nunzio1
    replied
    I do thin stainless steel, aluminum items for manufacturing of tea bags and at home in my shop I'm working on a monster mini-bike with a chrome moly frame, hydraulic disk brakes, 16 hp Briggs V-twin motor, 25 inch diameter by 12 inch wide knobby tires - it will be 8 feet long from the front tire to the back tire, standard fork rake (not chopped or extended. I'll try and attach a photo...

    Leave a comment:


  • arcdawg
    replied
    nunz, welcome aboard........ what kid of welding do you do in fairfeild ???

    im in the danbury area....

    brian

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  • Nunzio1
    replied
    Difficulty starting arc

    We had a similar problem with a Lincoln 250 mig - it would weld fine, then "bap,bap,bap" instead of a nice steady "sizzle". To make a long frustrating story short: The feed roller mechanism was poorly designed from the factory and would intermitantly not feed at a consistant rate. In comparing the construction of the feed rollers on the Lincoln to that of my Miller- the Lincoln used a metal roller with a plastic center core which allowed it to deflect under pressure - the Miller is all metal... The Lincoln rep finally replaced the entire wire feed unit and that fixed the problem, but this was after we replaced the gun, drive rollers, and after many frustrating months. The local Lincoln rep was not interested in solving the problem, and we had to embarrass the salesman at a Hot Rod show in front of alot of prospective customers into helping us out. I have always used Miller welding equipment and never had the problems that I had with the that Lincoln, nor have I ever had a problem with the service that I get from Miller. One other thing that might be happening is that when you first start a bead, the shielding gas may not be adequately at the end of the gun - I will pre-purge the line by pulling the trigger and letting about 6 inches of wire come out(without grounding out), snip it off and then begin welding. This seems to produce more consistant beads for me.

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  • prostreetboy
    replied
    Everyone,

    I appreciate the help and will try all suggestions.

    Dave

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  • timw
    replied
    You did not say age of machine or condition. If other suggestions don't help I would look at wire, is it clean, no surface rust, proper size for your work, spool too loose or tight, wire feeding straight or crossed on itself, is liner sticking, rollers right size for wire, ajusted properly, do you run torch lead out as straight as you can? Lets wire feed smoother. Also make sure there is no fan or moving air, it dosen't take much to blow your gas away. Good luck.

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