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Thread: Full Size Uzi Pistol Build Issue

  1. #1
    Registered User Ocean_Faux_'s Avatar
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    Full Size Uzi Pistol Build Issue

    Hi! I'm new to these forums, but I am searching for some input on trying to get my uzi build running. I've basically already completed it, but I'm running into an issue where the barrel/trunnion section keeps trying to cant up and down moving the primers out of the way of the firing pin. I've cut and welded and cut and welded over and over trying to get the receiver and trunnion sections to stay aligned, but every time I finish the weld, I fail to be able to remove the barrel without tools and the barrel is canted just enough to keep the firing pin from hitting the center of the primers. I am doing this build without a jig because they are either unavailable or way too expensive to justify for a single build use.

    The top cover and spacing all seem to fit just fine, my issue is just getting the trunnion to not warp up and down when I weld. The only issue is getting the barrel and bolt to line up sufficiently to fire. It cycles and ejects fine.

    This is my first kit build BTW, I've spent about 3-4 hours a day for 5 days (with one day totally practicing on scrap) on the build portion, and like 6 months on parts gathering here and there when I had the time and money. Its also sorta my first-time tig welding. They trained me enough to get the welder to work in my earlier schooling, but this has been a real test.

    I have one more 3 hour build day available to me this Monday before I have to have surgery Wednesday. I'm antsy because I don't know how long I'll be down after it and, I was hoping to finish the build before I head into my last semester of school. and anything that can speed up this process is greatly appreciated. Thanks!
    Last edited by Ocean_Faux_; 07-24-2021 at 07:34 PM.

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    An aligning rod is handy if not indispensable. The feed ramp is pretty much a fixed point so that needs to be welded in first. The aligning rod is stepped in the back end to fit into the feed ramp. From that point forward, the rod should be the same diameter as the trunnion i.d.. With everything dry fitted, the rod will set the trunnion elevation and angle. Sounds like bonehead advice but make sure the trunnion is in with the barrel nut catch slot up-- 12:00 position.
    Welding the trunnion is just a matter of tacking it in place, one side then the other in the rear slotted holes. Once those tacks are done, let it cool down to room temp and check that the rod slides in and out without binding.
    Next do the same through the front slotted holes and recheck. Once you're satisfied that everything is in alignment, TIG weld (better heat control) the trunnion through the rear slotted holes and let cool. Last, do the front slotted holes and you're done with that phase.
    This may sound like being overly cautious but screwing up then having to cut the trunnion out and redoing it is an easy way to find yourself in need of another trunnion... or receiver.

    Welcome to the forum.

  3. #3
    Registered User Ocean_Faux_'s Avatar
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    Unfortunately I decided to play hard mode and I'm currently building a pistol from a parts kit on an 80% with an intact rear leaf, and a front weld-on section. I wish I'd gone back and made it easier on myself, but the problem is more like the entire front of the reciever shrinks up and down and moves the barrel.

    Also thanks!

  4. #4
    Registered User NorincoKid's Avatar
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    I recently did a full size pistol, and wished I had the jig and/or alignment rod.

    I got it pretty close by eye, but still wound up having to cut the front off and redo it. It "pulled down" in the front quite a bit. I had a similar problem with the barrel being canted and the extractor on the bolt was hitting the 9mm case wrong and wouldn't engage.

    What worked for me was using some folded beer can scrap as a shim, and clamping the barrel down while welding.





    I did a small tack at the top on each side, clamped the barrel as straight as I could, tacked the bottom on both sides and then did the seams. It stayed put.

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    Sheet metal moves quite a bit. First because the thin gauge has less strength than a piece of 1/4" plate for instance so heating has more of an effect. Same with cooling down. Without a jig, clamping to copper weld backs act like a fixture and as a heat sink.
    Second, lots of tack welds, put in on opposing points, makes the piece more rigid when you're ready to do the final pass. As always, not creating too much heat will cut down on the chances of warpage so short passes on opposite sides are better than long passes. I suggest TIG welding thin stuff because the heat is more pinpoint than spread around like MIG and stick welding seems to do.
    Preheating is a good idea when practical. A piece heated to 300 deg before welding won't move around as much because the differential between work piece temp and weld is closer together. Slower cool down times will help too. When our welders are done, the piece gets shoved into a container of dry kitty litter or even wrapped in old welding leathers, then taken out when it's room temperature.

    Taking the extra time when welding is shorter in the long run and less aggravating than having to cut pieces apart and doing them over.

  6. #6
    Registered User Ocean_Faux_'s Avatar
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    Quote Originally Posted by NorincoKid View Post
    I recently did a full size pistol, and wished I had the jig and/or alignment rod.

    I got it pretty close by eye, but still wound up having to cut the front off and redo it. It "pulled down" in the front quite a bit. I had a similar problem with the barrel being canted and the extractor on the bolt was hitting the 9mm case wrong and wouldn't engage.

    What worked for me was using some folded beer can scrap as a shim, and clamping the barrel down while welding.





    I did a small tack at the top on each side, clamped the barrel as straight as I could, tacked the bottom on both sides and then did the seams. It stayed put.
    That is similar to the method I was using before I gave up last weekend. How, much did you find it to be shrinking. I used a thousandth's shim, but I don't know how much I need to prevent warping. it shrank and warped back up when I tacked the tops anyway. maybe a few extra layers of shims and some bending will do the trick.

  7. #7
    Registered User Ocean_Faux_'s Avatar
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    Quote Originally Posted by Jones View Post
    Sheet metal moves quite a bit. First because the thin gauge has less strength than a piece of 1/4" plate for instance so heating has more of an effect. Same with cooling down. Without a jig, clamping to copper weld backs act like a fixture and as a heat sink.
    Second, lots of tack welds, put in on opposing points, makes the piece more rigid when you're ready to do the final pass. As always, not creating too much heat will cut down on the chances of warpage so short passes on opposite sides are better than long passes. I suggest TIG welding thin stuff because the heat is more pinpoint than spread around like MIG and stick welding seems to do.
    Preheating is a good idea when practical. A piece heated to 300 deg before welding won't move around as much because the differential between work piece temp and weld is closer together. Slower cool down times will help too. When our welders are done, the piece gets shoved into a container of dry kitty litter or even wrapped in old welding leathers, then taken out when it's room temperature.

    Taking the extra time when welding is shorter in the long run and less aggravating than having to cut pieces apart and doing them over.
    I am on like re-cut 7. I am well-acquainted with failure at this point. I really appreciate the tips, though. I'll post any progress I make when I get over my surgery wounds in a few shorts weeks.

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