Welding is done on this project. It was a long but productive day at TechShop. Unfortunately I didn't stop to take any pictures.
First up was milling some scrap steel down to the correct thickness for the side plates. That meant figuring out how to use the t-slot clamps. Put the metal on a sacrificial piece of aluminium scrap and gingerly navigated an end mill around the clamps.
Once that was done, painted the scrap with "Prussian Blue" (layout fluid) and transferred the shape of the voids to it. I meant to bring in a pencil so I could do a rubbing on to scrap paper. But as it turns out, my hands were grimy enough from milling down steel I just needed to rub my fingers across the receiver to transfer the edges I needed to the paper templates.
Cut the bits out with the band saw, used grinding wheel and files to get the final fit, then superglued them in place.
Logged out of the mill and hopped on a vacant lathe; milled down a 1" chunk of aluminium rod to make a backer for the new welds I was going to be putting on the threaded end of the receiver tube. And fit the barrel plug back in to protect the space in front.
And then it was on to the MIG. I was getting good welds on a piece of scrap, so I didn't change the settings that were already on the machine. Welded the filler pieces for the side plates, tacked the front filler in place, filled a couple voids elsewhere.
So maybe aluminium backing is not the best choice. It took grinder, cold chisel, and pipe wrench to get the backing pieces back out again. But once they were out, clean-up in the voids they had filled was minimal, so perhaps it was a good thing after all.
The usual round of angle grinder, Dremel, then lots of hand files (I chose these because they are more accurate and allow me to get closer to a flat profile -- grinding tools tend to dish out).
I was very happy when the trigger group dropped back in. I thought the end cap was going to take a bit of work, but it also spun right on. The furniture is tight, though; I still need to remove some metal right near the magazine well. And even though there is visible warpage around the magazine well (some of which may be original, the remainder is probably largely from the demiliterization), the magazine catch and a test magazine both slide right in.
So most of what is left is drilling a few holes, final clean-up, and an attempt at bluing.