Suppliment to the posting on "welding thin metal".Steve is very right in saying that all welding machines are not created equal. This is true for both the small cheap MIG's up to the biggest of the 3 phase and engine drive industrial machines with 400+ amp outputs. I'm a bit partial to Miller because they are what I own and use the most of. (I'm very happy for that too) Just a little background on me before I get someone PO'ed at me for bragging on Miller. I have been welding for about 18 years. I started on the old Lincoln AC 225 amp buzz box (which my dad still has and uses). Over the years I have own many makes and types of welding machines. Amoung these have been Airco, Miller, Hobart, Lincoln, Campbell Hausfeld, GE, Westinghouse, Harbor Freight (central electric), Marquette, Century, Esab and a few other's I can't recall off hand. Back when my welding was nothing more than making two pieces of metal stick together, the old buzz box worked fine for me. As time went on, welding became more of a refined art requiring bigger and better machines. Now, I make my living doing this work so speed and quality are most important. Because the Miller's are designed for the pro doing production type work, they often run hotter and faster than other machines of the same size and type. Having gotten used to this, I find it very frustrating and stressful when I have to use a lesser machine, like yesterday when I was forced to use a Lincoln IdealArc 400dc. This machine may be "ideal" for lincoln but I would rather see it used as a door stop not a welding machine. The older stick only machines like the motor generator and engine drives have thier place even with me till this day. I have a 1940's something GE 300 amp that I won't part with because it's great for running bare manganeze rods. Despite the fact that is sucks up more power than I like paying for and it weighs in around 800 pounds, it does some work better than the turbo charged high end machines. Where I get into hating a machine is when I need to run a rod or wire in a manner that is often not consistent with what it was intended for. The Lincoln I used yesterday would not drive 1/8" 6011's the way I needed then to run and the job took about 6 hours longer than what it should have. When choosing a machine, you need to get one that is fitting of not only the work you do but also the skill level you have. For someone who never ran a rod before to grab my Miller Dimension 652 and try to run a V-up with a 7/32" 7018 it would end up in a melted blob at their feet. On the other hand, I could give them the old GE and have them running a decent V-up with the same rod in a few minutes. The arc and current characteristics of the machine can vary greatly from one model to the next and from one MFG to the next as well. This is why someone may have a brand X 120 volt 80 amp mig and you buy brand Y same size and it won't weld for crap. Because of this, you must be willing to experiment with the machine to see what is going to work best for it and for you. Like Steve said, the polarity is different for solid and flux cored wires. Solid runs reverse (electrode positive) and flux cores runs strait (electrode negative). In the small MIG's this may mean the difference between night and day. In put power stability is also a major concern with these small machines. The big industrial ones have what they call power factor conversion circuitry in them. I don't know the whole inner workings of it but what it does is stabilize the output even if changes take place on the input side. While these big machines may be able to handle input voltage swings of 30 volts or more, an input swing on a small mig of 3 volts may cause problems in the weld output. I suggest trying machines before you buy them. I know this is often not possible but try asking around for someone who owns one you can play with a bit. Try doing what you intend to do with it and see how you like it or hate it. After the years of practice I have, I usually set my machine to run one way and modify my actions to do many different welds with it on that setting. Thus, for my stick welding, I will usually set the machine for running a V-up fast and hot the way I like it. At that setting, I will do any weld in any position without changing the machine setting. For overhead, you keep the rod straiter and wip it a bit, same goes for horizontal. When you often times work several hundered feet away from the power source, you don't want to change settings everytime you change weld positions. For MIG I tend to be a bit more fussy about how the machine runs. Too hot and you can't hold a V-up and too cold and it will not run a flat and get the bite in the weldment I want. This is when practice pays off. You can run hot with a MIG and still maintain an all position setting if the machine and wire are both compatible with what you are doing. What I'm getting at is there is no one choice that fits all users. If you are buying a machine for a specific use, you need to get one that will preform the way you need it too but still be user friendly enough if you don't have the practice to work around the internal problems of the machine. You may find that you can run a self sheilding wire easier than a solid wire and vice versa. The common problem I see with DIY'ers and welding is they don't know what a weld is supposed to run and look like and can't adjust either the machine or themselves to get a good weld. Before you buy anything, I strongly suggest you take some welding classes at nights or on weekends to get a feel for what is supposed to happen and what you are looking at. Remeber, no matter how old the dog, there are still new tricks to learn every day. I'm still learning too. BTW, I still hate welding flat with a stick! V-up or overhead for me!
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