Back to the Suomi. To recap; it started as a demilitarized kit, meaning all original parts except someone at the ATF took a plasma torch to the receiver. I ground off all the slag from the bits of receiver, and machined a jig (in the form of a fake bolt with a barrel plug attached to the front) out of aluminium.
Yesterday, I tried the first welds. One of the theaters I work at has one of those cheap wire-feed welders -- the ones that will plug into a household wall outlet. And I made a nice hedgehog.
(In my defense, besides being rusty, and more used to stick welding anyhow, I didn't have good light and could only really see the arc -- which is not quite enough to really see by.)
(This isn't the full hedgehog glory; I've already knocked off some of the slag and given it a quick wire brush.)
And it seemed to work. I was worried about filling the wide gaps, and worried about the aluminium backing. Well, the latter survived without real issue, and I was able to remove the most-stuck one with a few twists of a wrench. The former, it turned out bridging was relatively easy, but I didn't get as much metal down inside the gaps as I would like.
Flux-core wire is very slaggy stuff, and you tend to get a lot of voids and inclusions with it. I made it a point of puddling until I could see metal glowing (about the only thing I could see!) and that seems to have floated much of the slag to the surface.
And then to grinding -- mostly Dremel so far, plus a whole bunch of hand file work. I expected this to be the worst bit; the plasma torch cut is right across where the lugs mate with the rest of it. And it turned out I'd made one mistake in alignment; I put the piece in about 1/16th of an inch too close, meaning I had negative headspace.
But it made it all the same. Barrel and shroud sit tight and feel solid. Now to do the other two welds!
(Post title is a reference to one of the songs in "Mary Poppins" -- in fact, my favorite in terms of the orchestration. There's just this lovely little period brass oompah going on under that one.)