The Home Machinist!

Hello All,

Just bought a new Millermatic 255 mig welder. I set it up with an 11 # spool of P3 .035” wire from Airgass. Have had nothing but trouble with the wire... or machine, not sure which at this point... after about an hour of doing a bunch a short welds on 3” steel channel, experienced numerous problems feeding the wire through the gun. I loosened up the spool settings several times, but the wire still comes out knurled, and at the last, started immediately burning back into the tip. Several times in a row as soon as I hit the trigger. Each time with a burst of blue flame and actually watched the wire vaporize right up into the tip. Had plenty of stick out etc each time. It’s as if the voltage took a huge jump and just vaporized the wire as it came in contact with the work.

Observed burnout frequently when the gun was hot and starting in an overhead, or vertical weld. Make a normal horizontal,weld .- no problem. Try vertical - burnout immediately.

Also, the wire itself was wrapped poorly and buried in the spool in numerous places. I ended up pulling off and throwing away several hundred feet as it wouldn’t come off the spool without a lot of random feed problems.

Anybody know if these are common problems with this P3 wire. Wondering if this wire is known to be problematic, or if something else is going on with the leads or gun?

Thanks
Glenn

I'm familiar with an Airgas, but not an Airgass. I use the former's P/3 wire in my Century MIG welder in both 0.030" and 0.035" sizes, and have never had a bird's-nest problem as you are experiencing.

The symptoms you describe suggest the wire is being fed too slowly for the machine's voltage setting. I presume you are using the correct-size gun tip and the correct-size wheel in the feeder mechanism. Also, is the wire spool able to freely rotate? A little bit of drag is okay, and is preferred to prevent the spool from coasting and unraveling wire. A lot of drag will give you no end of grief, as the spool will lurch, causing an abrupt change in feed rate.

BDD, yes correct tip and wheel size. The machine is so new I don’t know what is normal or not. It does seem like the spool of wire was not turning at a uniform rate... although I read miller’s have a slow speed start up wire feed. Still it seemed jerky at times. Also all my problems were with the gun twisted upward. Maybe the wire is binding in certain positions somehow... I’ll work through the list.

Thanks ,
Glenn

It sounds like the voltage settings are way too high and the wire speed is too low by it vaporized back into the the contact tip on the MIG stinger. Vertical welding are you welding up or down the peace of metal? For overhead welding you have to set the welder for horizontal welding (i.e. settings that are required for the thickness of welding in the horizontal position), I normally lower my voltage just a little bit for welding overhead like only by -0.3 or -0.4 from your normal horizontal welding settings this helps preventing less splatter falling on you and the peace that you are working on. If you are welding vert down you have to move quick to keep the puddle from running and pooling up and not getting any penetration in the toes of the welding puddle. If you are still having trouble with it look up on YouTube welding tips and tricks the person that makes these videos are very helpful and he goes in depth with each position of welding for all types of welding styles.

Andrew S.

Thanks Andrew,

High voltage, low wire speed sounds right, but worrisome as I was welding fine for an hour or so before this started to happen. I was doing vertical down on a new spot on the frame. And didn’t get a chance to even start the puddle before watching the magic blue flash. Several times in a row.

Also, interestingly, the 255 is a new model. It has a series of automatic settings that Miller preprogrammed for voltage and current/wire speed. So very surprised when it started acting up.


The gun was rather hit by this time. I am wondering if the heat somehow distorted the tip or mechanism causing the wire to drag??
Glenn

Your machine has what appears to be a Tweco-style gun, which is a common type. My welder has one as well, and I have never had any problems with it. Most likely, the repeated burn-back of the wire into the tip has damaged the latter.

As for the preset voltage/feed settings, I wouldn't rely on them—there are too many variables. The "old-fashioned" method of tuning the feed to the voltage remains the best way to get things just right, especially if making out-of-position welds.

BTW, what are you using for shielding gas and at what flow rate are you using it?

Glenn:
Be sure to install a new contact tip. Especially after trying overhead welding when crap can get on/in it.
I learned that after any burn back, the tip required replacement to prevent the wire from dragging inside the hole.
Every time. It was a huge relief to learn that a new tip resolved my welding issues. I bought a bunch of replacement tips and use them freely.
That was with my Hobart machine.
RussN

Thanks, yes I replaced the tips each time- 4 times in a row before giving up for the day....

Gas is 75/25 mix at 50psi...

I've never seen welding shield gas regulated by psi. Typically flowmeters are used. 50 psi seems high to me.

Glenn Brooks wrote: ↑Mon Jun 07, 2021 4:09 amGas is 75/25 mix at 50psi...

Shielding gas flow is metered in standard cubic feet per hour (SCFH), not by gauge pressure. For most applications, 15-20 SCFH with 75/25 is a suitable flow. If I'm doing heavy, overhead welding, I might increase that to 25-30 SCFH, but never that flow rate for horizontal or vertical welds. Excessive gas flow will cause the arc to be unstable and weld quality will be poor.

Yep, I misspoke. It is indeed CFM, not psi. So set up at 50cfm. What Miller recommends for this particular machine...

But I don’t remember them differentiating between horizontal and vertical. See to check that...

Glenn

Glenn Brooks wrote: ↑Mon Jun 07, 2021 6:42 pm Yep, I misspoke. It is indeed CFM, not psi. So set up at 50cfm. What Miller recommends for this particular machine...

But I don’t remember them differentiating between horizontal and vertical. See to check that...

Glenn

50 cubic feet per minute? No way! You'd empty your cylinder in a couple of minutes.

15-20 standard cubic feet per hour is considered typical for welding low- to medium-carbon steels in flat or vertical positions. A higher flow when overhead welding aids in reducing the amount of spatter that gets back into the nozzle and in my experience, causes the puddle to solidify a little faster, reducing a tendency to drip. In the Millermatic 255 manual, they state the following:

Typical flow rate for shielding gas is 20 to 30 CFH (cubic feet per hour).

I run mine at 15, except when overhead welding or working with thick sections where I have crank up the voltage.