MM 250X - difficulty starting arc

[prostreetboy]

Hi everyone, long time reader, first time poster. I have a MM 250X, using C25 gas that I'm using to build a '37 Chevy prostreet car. The problem I'm having is the consistency of starting the arc. Sometimes it will go right into the "frying bacon" sound - no spatter - nice weld. Other times, the wire will pop and burn back the contact tip (usually getting stuck)with spatter going everywhere. I've played with the feed and voltage w/o much luck. It's especially frustrating when I'm trying to do a bunch of stitches on body panels. Any suggestions?

Dave

[arcdawg]

make sure that your ground is on a nice and clean piece of metal. then worry about your STICK OUT, grab some scrap and try it out before you kick the welder or the car

brian

[cope]

Try posting this at the Hobart site. Dan over there uses a 250 at work I think and has some input on them.

http://www.hobartwelders.com/mboard/

[HAWK]

prostreetboy,

When working on body panels you definitely want the mig welder producing a crisp crackling short arc. Stick out, as arcdwag mentioned, is the primary culprit in inconsistent welds. If all other parameters (wire speed, voltage, gas flow) remain constant, then look to operator technique. Keep the torch in close to your work and the wire at the leading edge of your puddle. A very slight weave motion may help you in this case. Once you find a torch to work piece distance that produces good result, concentrate on repeating it.

[timw]

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.

[prostreetboy]

Everyone,

I appreciate the help and will try all suggestions.

Dave

[Nunzio1]

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.

[arcdawg]

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

im in the danbury area....

brian

[Nunzio1]

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...

[ASKANDY]

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

[prostreetboy]

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

[Nunzio1]

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.

[prostreetboy]

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

[lmaini]

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/showthread.php?threadid=3450&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

[prostreetboy]

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