I heat treat the lower rails before I install them. The best way I found to align the lower rails in a flat so they were both parallel with the upper rail and aligned with the trunnion was to use a drill bits of the proper size to locate the lower rail and I would then clamp the lower rail in place prior to spot welding. This is one of those things where you want to check and double-check prior to and after each weld to make sure nothing shifted on you.
I use a Harbor Freight #45689 115 Volt spot welder with AK-Builder upper replacement tong and also tips. It’s lasted me through quite a few builds over the years and is still going strong. The tong makes it way easier to reach in and make the weld and the tips make the spot weld look a lot more like the real ones. I have had to replace the tips once so far, just FYI. You need to keep them clean to be most effective.
For beginners, there is no way to tell you how long to clamp and trigger the current for – many factors can affect how long it takes to heat the steel up enough for the two pieces of sheet metal to weld together. You need to practice and you’ll notice the color, sound of the welder. the amount of time it takes to get a good weld and especially the feel of the clamps as they come together during the weld. With practice you’ll feel when you have a good weld especially but it all adds up but you need to actually do it to learn.
Get scrap metal of about the same thickness to practice with. AKM receivers are 1mm thick. 18 gauge is 1.02mm so it is good to practice with and old scrap receiver stubs are another. With your first practice weld, go long and let the pieces really melt together so you can see. You want to burn a hole to understand how long it takes, the sound and the feel of the tongs. Then practice with less amounts of time until you find the sweet spot. These welds should be pretty strong and not pull apart easy. I do more spot welds than most and some guys look at photos of the rifle they are building and try to approximate the count and location, which is just fine. One thing, if you do heat treat your rails before hand like I do, be careful you do not get the tongs up against the ejector and ruin the heat treat. I’ve done it and the tell tale sign is that the ejector will be discolored from the heat. If you do make this mistake you will need to heat treat the tip while it is in the receiver or else it will definitely peen over and be deformed in its softened state. By the way, the steel should be relatively clean also and not have tons of grease or other contaminants on it either that might inhibit a good weld.
Just double check alignment very carefully before you spot weld and also that your welder’s tong does not get against the ejector and ruin the heat treat – assuming you did that before installation.
I hope this helps you out!
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