I was asked to provide pictures and review of the Lincoln SG100 Spool gun, so here goes (you might want to get a cold drink, this is a bit long winded)…
I’ll start with the bottom line; is it worth the ~$200 – yes. It makes MIG welding aluminum significantly easier. The actual welding is not any easier, rather the SG100 takes care of “nearly all” the wire feed problems associated with MIG welding aluminum with a conventional pusher system. I’ll get into the “nearly all” bit in a moment.
Next, I want to stress that I’m not a pro-welder. I’m a self taught hobbiest. Chances are, some of the welding techniques I’ve learned/developed over the years (that work for me) aren’t 100% correct. So take this review with a grain of salt. Individual results may vary and if you have more or less success using a SG100 (or any spool gun), please share your experiences as well.
Set up – Either there was not complete information in the Lincoln website, or I simply didn’t pay enough attention, but I was put under the impression that to hook up the SG100 to my Lincoln ProMIG 175, I would need an adapter kit that wasn’t available through Lincoln. Like the good little lemming, I quickly ordered a SP125 kit from Oxarc.com.
http://shop.oxarc.com/lincoln-elect...oolgun-to-sp-100-sp-130-sp-175-model-welders/
(This is not an endorsement or negative critique of their product, only to say it worked). Turns out, the only part needed out of the Oxarc kit, is the female plug receptacle that gets mounted in the front panel of the MIG welder. The rest of the wire, terminals and switch were included with the SG100. It irked me a bit to spend $50 for a simple part. Someday when I have nothing better to do, I’ll peruse the electronic resources I use to find an appropriate plug receptacle for less $$.
Budget 2 hours for installation. Some folks will finish the work in far less time with far less profanity . . . I don’t like any of you. The descriptions and graphics in the instructions (in my case) didn’t exactly match the innards of my older ProMIG 175. It was a little scary messing with the wiring inside the welder while not being 100% certain I was doing the correct thing. A little deductive reasoning and circuit chasing proved to me I was doing things right.
A word of caution, before drilling the required holes for the switch and female plug receptacle, take a moment to mock up where these items will be installed and evaluate that you actually have enough wire length to place these items where you are instructed. In my case, the wires for the switch were a bit too short to make things easy. I ended up routing wires outside of the stock insulated wire loom to gain the needed length. It might have not been necessary, but I salvaged a bit of insulating wire loom from a PC power supply to protect the re-routed wires. Conversely, there was ample wire available for the female plug receptacle and I could have positioned it where it looked a little better.
Use. Again, this is just my experience, but to weld using the SG100, I had to toss out the journal I kept of what setting worked for what aluminum conditions. Using the spool gun required less amps (about 20% less) and slower wire speed. Also the wire speed out of the ProMIG 175 internal drive system is about half of what the SG100 puts out. The wire flat out screams out of the SG100. I ended up welding with my wire speed setting at about 60% of what I was accustomed to.
It seems that the electrode tips used on the SG100 have a propensity toward melting. Settle down all you pro-welders out there…I’m sure it’s something I’m doing wrong, but in the 10+ years I’ve been MIG welding aluminum, I’d never actually melted an electrode tip. The electrodes that fit the SG100 are tapered versus a blunt tip like I’d been using for years (and of course, they’re not interchangeable.) Maybe the lack of material makes them more prone to melting. So with that said, expect to turn down the amps and wire speed. It wouldn’t hurt, before you get started, to find and purchase a package of electrode tips. I paid about $8 for a pack of 10. (Also, for what it’s worth, I also drill out the .035” tips using a 1mm drill bit to ensure any inconsistent wire condition won’t cause the wire to stick.)
The wire drive system in the SG100 could stand for some improvement. The pressure roller is not adjustable. It’s basically a sealed roller bearing on a spring plate. Prying the pressure roller away from the drive roller to load new wire (or put the misaligned wire back in the groove, more on this in a bit) is not the easiest chore. When prying the roller out of the way, the little engineer in your head will be convinced you over flexed, and permanently deformed the spring plate. I sacrificed a tiny flat blade screwdriver, bending the end, to make a tool that made this task easier. The pressure roller doesn’t have much support. In fact it appears to be only balanced on the edge of the spring plate.
This allows the bearing to pivot, which allows the filler wire to slip out of the drive roller groove and get stuck under the pressure roller bearing. This is made worse by poor quality wire (BTW, it was the spool of .035” 4043 that came with the SG100 kit). I’m working on a solution to the pressure roller dilemma and will share the fix when ready. So the long, profanity laced tirades that used to be commonplace while trying to feed aluminum wire through a 10’ torch cable or unf*cking a birdsnest, were replaced with a new tantrum brought on by the weld wire suddenly stopping, leading to yet another melted electrode tip.
Again, find and buy a supply of electrode tips. The kit only came with 5 - .035” tips and I melted 4 inside of 15 minutes while I figuring out this new system.
Yet you still don't give an example of what you want to weld. 
Within reason. Even the 250-class don't really have enough snot to run some 1/16" solid steel ER70S-6 wire in spray mode with C10. Nor some 3/32" Lincoln Ultracore 70C FCAW-G wire (which, with enough machine, can be put down to the tune of over 20 lbs of weld bead per hour!). Just saying. 
