Bead feedback

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Made some practice beads with my new (to me) Millermatic 250. From my limited experience I think most of the beads look good, but what I'm really wondering about is what the back side of the metal should look like. After looking at the back side of my first bead (right side of both pictures) I guessed that I was moving too slow and that was letting the metal burn through too much, so I sped up after that. The weld was always still visible on the back side, which I assume it should (for thin metal like this 14ga, at least), but how visible should it be? Should I be shooting for welds like the 7th from the left, where there isn't really much weld sticking out on the back, or should I be shooting for something more like the 5th from the left where there's a small, reasonably consistent bead visible on the back side? And how does the story change if using thicker metals? Should you still see anything on the back side if welding, say, 1/4" plate?I tried to angle my gun around 10-15 degrees, basically just enough to still be able to see the puddle while having my gun pretty close to the metal, the and was pulling back left to right as opposed to pushing forward. Actually, one of the beads was done pushing forward, right to left, but it didn't feel as comfortable to me so I just kept pulling instead. I don't remember which of the beads was done with pushing, but I guess since I can't figure out which just by looking at it then maybe it doesn't really matter?The metal was 14ga, and I was using approximately the values given on the chart in the machine: 17.5v and 170ipm (40% on the low speed setting, which is 50-350ipm). 0.35 wire with 20cfm 75/25 flow.Any advice is appreciated! - Ian Attached Images
Reply:A little bit too hot Ian cos its coming through the other end Apart from that mate they look pretty decent to me
Reply:On 14 ga you will want a less penetration than I see there. Settings for 14 ga, .035 wire, 75/25 should be around 16.5v, wire speed around 190 roughly. If you download the manual from Miller I believe it has the suggested settings in the manual if they aren't under the cover.Push vs pull. FC wire is always drag or pull. Solid wire is usually push, though there are exceptions to this. Push gives you a bit less penetration, which is definitely a plus with thinner sheet stock. Most mig students I deal with want to sit behind the gun and try to look around the nozzle. That doesn't allow you a good view of the puddle. Thus they naturally want to pull or drag the weld. You need to get your head out front of the gun and look down the barrel for an uninterrupted view of what is going on. I typically will set up so I'm not welding directly right to left ( I'm right handed) but at an angle, so I'm starting farther away on the right side and moving both closer and to the left at the same time as I lean out in front of the gun. On longer welds I'll almost weld straight in towards myself, and move my whole body backwards away from the gun if that makes sense. ( It's easier to show than explain in reality)As far as which one you pushed, I'd guess it's the one that shows absolutely zero burn thru on the back. That matches some of what I see on the front as well, but it's a bit tougher to tell from that side..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Awesome, thanks guys!The settings I was using came from this supposedly MM250 chart that shows 17.5v for 14ga/0.35: http://www.gowelding.org/images/Mill...ting_Chart.jpg  So I thought maybe the burn-through was expected to a degree. I'll try again with lower voltages.I'll also work on pushing instead of pulling. It did feel less natural because of the reason you mentioned DSW: it was harder to see the puddle. I was looking straight down onto the metal, with the 10-15 degree tilt being the only thing that really got the nozzle out of the way to see the puddle. I'll work on getting out in front of the gun to look more horizontally under the nozzle to watch the puddle (so in my right-handed case, my head will be off to the left relative to the gun). I think your diagonal movement also makes sense, since that would require my head to be less to the left and more "towards me", which would require a bit less head tilting and more just "getting lower"...I think...Also, for a noob, does it make a difference what thickness metal I practice on? Would a thinner or thicker metal be more suitable for "general" practice?
Reply:I'll agree that's what  you chart shows. My copy on my desk comes out of the manual for the MM 252, You'd think they'd be the same since voltage is voltage, and the numbers on the MM252 chart match up to what we run on the XMT's at the tech school.As far as material thickness, all depends what you want to work on. It's sort of silly to practice welding 3/8" plate if you are doing auto body restoration. On the other hand welding 14 ga won't help as much if you need to get an unlimited mig cert on 1" plate. Tech school does most of it's welding with 1/8" material. In general they also tend to set the machines hot since many of the guys will try to get a job at a local catalytic converter place and will need to mig thinner stuff fast ( place want to run hot and fast since it's all piece work). We also have 3/8" material that they use to do the 3/8" bevel but joints for those looking to do structural work. Once the student get's thru all his joints on 1/8", they can move on to do the bevels in 3/8" if they choose.1/8" is thick enough you don't blow holes in the material instantly, yet it's thin enough so you have to have some heat control. If someone was interested in just sheet metal body work, I'd probably suggest a bit thinner for general practice to start, say 14 or 16 ga instead, then move down thinner once they get the basics down. 18 ga and less requires a different skill set than thicker materials and often uses completely different techniques to try and avoid burn thru and heat distortion. It's a whole world unto itself in many ways..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan