Do you gap butt joints for Mig welding?

[clint738]

I'm working on some little projects (moving outlet locations in my shop and building braces to hang them on the underside of the c-purlin around the shop).

Previously the shop owner had welded the outlets to the top of the c-purlin, but I'd rather them be on the underside so I can set stuff on top of the purlin.

So I'm bending 3" wide 1/8" thick strap the weld to the underside of the purlin and then I will bolt the new water tight receptacles with covers to the strap.
In addition to getting the outlets the way I want them, this is giving me the opportunity use my new Millermatic 252 and become more familiar with Mig welding with shielding gas. All I had ever used with my MM140 was flux core.

The question I'm having is with bead height. It looks like the majority of the weld it pretty tall in height so I'm wonder what ways (techniques) to use to smooth it out?

I'm using the recommended Miller settings for 1/8" (17.4V and I think 230ipm and shielding gas (75% argon 25% Co2) at ~24cfh.
I have the material butted flush with basically no gap.

I did have a few pieces where there were gaps and the weld flattened out more until it started to (key hole I guess its called) basically burn through which was fine until I got to far ahead and the wire just poked through the hole without touching material causing my arc to stop. Then I had to restart.

So I'm wondering what would be the best way to setup the material for Mig?

I just got the material from the steel supplier and it was all kept indoors so I didn't bother grinding the material where I was welding before hand.
How important is removing the mill scale? I didn't have porosity.
I just need to get use to watching the puddle looking around the big mig nozzle so I can weld where it is suppose to go. Also getting use to a new fixed shade #10 I have in a new jackson hood I bought. I like the headgear in the new jackson better than my +10 year old jackson hood I have. I have found keeping the gun perpendicular with the material helps to flatten out the weld some.

[tackit]

You don't have to gap every joint. if you're welding something that needs to be plumb you leave a gap so you can tack it plumb to it's base plate, like a tube or pipe used for a grinder stand .......or if a weld is critical and needs full penetration you gap a joint. The reason your bead is high could be your travel speed is to slow or your pulling rather than pushing the bead. You may have to turn the wire speed down for over head welds.

http://www.millerwelds.com/resources/video_library/

[clint738]

You don't have to gap every joint. if you're welding something that needs to be plumb you leave a gap so you can tack it plumb to it's base plate, like a tube or pipe used for a grinder stand .......or if a weld is critical and needs full penetration you gap a joint. The reason your bead is high could be your travel speed is to slow or your pulling rather than pushing the bead. You may have to turn the wire speed down for over head welds.

http://www.millerwelds.com/resources/video_library/

I'll try moving faster. I have a habit of moving slow from stick welding I guess. It looked like I was getting decent penetration between the two pieces just looking at the heat marks left on the pieces, but the bead height looked a little higher than I expected.

How wide should the bead be for Mig welding 1/8" plate flat butt welded?

I'll also try to work on pushing the bead. Once again, I have a habit of pulling the bead and not pushing from stick welding. I find I can watch the back of the puddle better when pulling the bead versus when pushing the bead I can't see the back of the puddle, just the leading edge of it.

[tackit]

I'll try moving faster. I have a habit of moving slow from stick welding I guess. It looked like I was getting decent penetration between the two pieces just looking at the heat marks left on the pieces, but the bead height looked a little higher than I expected.

How wide should the bead be for MIG welding 1/8" plate flat butt welded?

I'll also try to work on pushing the bead. Once again, I have a habit of pulling the bead and not pushing from stick welding. I find I can watch the back of the puddle better when pulling the bead versus when pushing the bead I can't see the back of the puddle, just the leading edge of it.

Just make your weld the approximate size of the thinest metal you are welding. It's a waste of wire go much bigger. The weld is stronger but the connection is only going to be as strong as the thinest size or guage of metal.

Try to keep your head a bit in front of the gun, you will see the puddle. Generally speaking pushing makes the weld smoother and lower. Sometimes you will have to pull, it's just what people like and the job your welding up. Try to learn both ways, you get the hang of it. Just remember wire feed speed is amps too, so if your welding overhead you might have to lower the wire speed from what the door chart says.

[clint738]

You don't have to gap every joint. if you're welding something that needs to be plumb you leave a gap so you can tack it plumb to it's base plate, like a tube or pipe used for a grinder stand .......or if a weld is critical and needs full penetration you gap a joint. The reason your bead is high could be your travel speed is to slow or your pulling rather than pushing the bead. You may have to turn the wire speed down for over head welds.

http://www.millerwelds.com/resources/video_library/

For over head do you just turn the wire feed speed down, or do you turn the voltage down and then also adjust the wire feed speed down some calculated amount?

The 1/8" strap will be welded to the 14AWG c-purlin overhead.

[clint738]

Just make your weld the approximate size of the thinest metal you are welding. It's a waste of wire go much bigger. The weld is stronger but the connection is only going to be as strong as the thinest size or guage of metal.

Try to keep your head a bit in front of the gun, you will see the puddle. Generally speaking pushing makes the weld smoother and lower. Sometimes you will have to pull, it's just what people like and the job your welding up. Try to learn both ways, you get the hang of it. Just remember wire feed speed is amps too, so if your welding overhead you might have to lower the wire speed from what the door chart says.

So lower the wirefeed speed but leave the voltage at the 17.4V value suggested on the guide for 1/8" material?

Also, when gaping the butt welds would you just gap the thickness of the wire used, sort of like how with stick welding you can gap to the thickness of the rod for open root?

[tackit]

Don't get caught up in the door chart numbers, I would experiment and see what wire feed speed and voltage works best for you on a particular weldment, those numbers are just to get you close. It's OK to adjust them to your situation. I go by how the weld sounds not the door chart's numbers.

[clint738]

Don't get caught up in the door chart numbers, I would experiment and see what wire feed speed and voltage works best for you on a particular weldment, those numbers are just to get you close. It's OK to adjust them to your situation. I go by how the weld sounds not the door chart's numbers.

well I did that on my mm140. I would set the dial for the correct material thickness and then dial the feed till it sounded right.

But with a voltage instead of a chart, i'm not sure what voltage for what thickness metal.. hence going off the door chart.

[tackit]

well I did that on my mm140. I would set the dial for the correct material thickness and then dial the feed till it sounded right.

But with a voltage instead of a chart, i'm not sure what voltage for what thickness metal.. hence going off the door chart.

Just think of the door chart as a starting point. It's not going to be that far off, you'll just be fine tuning the setting.

[Cgotto6]

Did you do any joint prep? If I want a flat appearance I have found it helps to make a place for the weld. So I will usually throw a little bevel on each edge then weld.