The Hobart Handler 187 is a wonderful 240-volt, 185-amp MIG welder that supports a lot of my engineering projects and fabrication work.

But the spool gun accessory I needed for welding aluminum on the gimbal project is compatible only with the top-of-line Handler 210.

The standard wand is designed for heavy welding wire like steel, which can be easily pushed 10 feet through the line. But aluminum is too soft for this.

There's a separate spool-gun controller available, but it's a $100 more than the spool gun itself.

One online welding supplier (BR Welding) sells a do-it-yourself adapter for $99 that supposedly works. This is what's in it (from their web site). Not much for the price, and certainly far fewer parts than in the SGA 100 above. In fact, as far as I can tell based on what I did and learned in my project, this adapter does not work!. In fact, even their customer support indicated that in some cases ("1 out of 10"), it runs too slowly (and there are no refunds). Go figure.

So it was time to put on the old engineer's thinking cap and look into this. Internally, the 187 and 210 are extremely similar units, differing mainly in capacity, not operation. (This is actually a common manufacturing practice across model lines because it allows shared parts, which keeps costs down.).

And quite a rarity these days, Hobart (and Miller, their sister brand) are actually American companies that make their products here the way we used to. In fact, they even do what was considered the norm in yesteryear: they include the circuit diagrams.

So at this point, it was time for a little MacGyver action (completely voiding my warranty, of course, but the unit is nearing the end of the period anyway). It took a few revisions (I'm not sure if this was the actual order).

I had to add a bypass switch to disengage the internal feed motor and redirect it to the motor in the spool gun. (This part is in the "Hobart Motor" box in my schematic diagram, which contains Hobart's entire schematic above it.) The redirect isn't this straightforward, though, because the two drives are substantially different in their electrical and mechanical specifications. In fact, this is the primary reason why the questionable adapter above can't possibly work. (And as a test, I tried a direct connection. Guess what, too slow!. I guess I'm that 1 in 10, right?).

So here's the little switch: up is spool gun, down is internal drive. I also had to add the white harness connector to the spool-gun cable — voided that warranty on the day it arrived!.

I know what's in the 187, and I can infer what's in the approved SGA 100 controller above, so my task was to make the same thing happen. This is a pulse-width modulator that controls the voltage to the spool-gun motor. It's triggered by the control circuitry in the main unit.

Moving the main unit around on the floor and bench is a headache. It weighs about 80 pounds, plus it's attached to a 40 cubic-foot cylinder of argon (which at this point, I guess I could have disconnected).