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  • Miller Thunderbolt XL 4 position switch

    Hello, I'm looking for help with my Miller Thunderbolt XL. I bought it used a bit ago. I had only ever tried it DC and it has been working fine. I tried to run some 6011 on AC for the first time and it didn't work at all. No arcing.

    Today I took it apart and was trying to figure out how it works to know what could be wrong with it. My main issue was that the diagram doesn't really tell me how the 4 position switch SHOULD work. I don't know what happened with the welder before I got it. It kind of feels to me like the switch isn't right. I think that the rectification portion is only for DC and should have no bearing on the AC function. Is that correct?



    So I went through and tried to figure out how the switch would activate the current. I couldn't even get continuity to the electrode or the work wire on low AC. On high AC I got continuity to the work wire but not the electrode.


    PS: I just wanted to look into this more before posting so I went back to analyze it a bit more. I noticed earlier that I saw some electrical tape in there and figured there wasn't much chance it came from the factory that way and someone had monkeyed with it. I decided to take the switch apart. Apparently they used some pieces of rods to push the copper connectors. I would think this should be spring driven to keep constant pressure, especially as the copper wore down and to make up for different tolerances in the contacts from one position to another. I was worried the plastic piece was broken and that is what the tape was holding together. It's actually still in one piece. I'm not sure how the original design worked or what is missing. If anyone has taken this apart and knows I would appreciate some information. I couldn't find parts for the switch, just the new replacement switch (239110 - https://www.millerserviceparts.com/P...roductId=13119) and it's not cheap at 100+, especially when I have a mostly good switch. I guess I'm likely going to have to buy it but with an idea of how it worked I might better be able to rig it in the mean time.



    Thanks for any ideas and also, is the link above the best place to get the full switch if I go that route?
    Last edited by jtap; 04-25-2020, 10:22 PM.

  • #2
    Yes, you are correct that the rectifiers are only for D.C.; they have nothing to do with the AC welding ranges. There may be someone here with an idea on how to repair the switch, but my guess Is you're going to have to spring for a new one. Hope I'm wrong. Good contact there is essential to the function of that machine. In addition to the Miller parts site you looked at, I checked Miller4less.com and BR Welding supplies; both are around $110-120.

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    • #3
      Originally posted by Aeronca41 View Post
      Yes, you are correct that the rectifiers are only for D.C.; they have nothing to do with the AC welding ranges. There may be someone here with an idea on how to repair the switch, but my guess Is you're going to have to spring for a new one. Hope I'm wrong. Good contact there is essential to the function of that machine. In addition to the Miller parts site you looked at, I checked Miller4less.com and BR Welding supplies; both are around $110-120.
      Thanks for the reply. I am thinking about buying a box of assorted springs from harbor freight and filling up the area with whatever I can fit in there.

      My guess is that it would have been possibly quite heavy duty. The thin nature of the slot makes me think it was the type where it was a coiled piece of flat metal (spiral spring) or a v spring of some sort. Leaning towards the V since I would think the coil would need an anchor point and I don't remember seeing one. It would be nice to know as that could help me find something with a similar mechanism to steal the spring from or to buy one most suited to this for another application.

      The problem with the compression springs is fitting it to the gap in the plastic though with it being long and thin. Any springs though should be better than 3 pieces of cut welding rod!

      Edit: Did some measuring and all the HF compression springs are too big for the channel. Pretty obvious the design is something else. It's going to be crazy when I try to cram 5 ball point pen springs in there and try to keep them in while I assemble it.
      Last edited by jtap; 04-26-2020, 09:55 AM.

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      • #4
        Let us know when $100 of your time has been burned up!

        That said, if you nail it good, and it stays together during full operation of the switch, well done!

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        • #5
          If you could find a piece of spring steel about the width of the channel and bend it into the shape of a "W" it may work. That or a piece of the spring from an old pistol magazine, if you don't mind cutting it up. It would frustrate me too that probably a 75 cent piece will cost me $100, but your next project will likely cost much more than that, so a new switch may outweigh that frustration.

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          • #6
            It is hard to get a good idea of what the original spring was like but from what I see in your picture I would guess a long flat spring like a mini leaf spring. What is the white stuff in the grooves? And what looks like solder or torn metal at either end of it? Maybe find some spring brass and fabricate replacements?

            ---Meltedmetal
            ---Meltedmetal

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            • #7
              Originally posted by MAC702 View Post
              Let us know when $100 of your time has been burned up!

              That said, if you nail it good, and it stays together during full operation of the switch, well done!
              Probably already spent that on research and taking it apart and posting here. Now it's just about being stubborn and solving a problem. I might as well sell the welder if I can't fabricate something to allow me to fabricate

              Originally posted by jjohn76 View Post
              If you could find a piece of spring steel about the width of the channel and bend it into the shape of a "W" it may work. That or a piece of the spring from an old pistol magazine, if you don't mind cutting it up. It would frustrate me too that probably a 75 cent piece will cost me $100, but your next project will likely cost much more than that, so a new switch may outweigh that frustration.
              Yeah, you bring up a good point with pistol stuff. I dug up an old hammer spring but it was just a bit too wide. I could have cut it into some pieces that would have worked well. Almost!

              I am trying to find an old sear spring that I could experiment with. Pistol parts could be the solution here. Thanks for the idea.

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              • #8
                Originally posted by Meltedmetal View Post
                It is hard to get a good idea of what the original spring was like but from what I see in your picture I would guess a long flat spring like a mini leaf spring. What is the white stuff in the grooves? And what looks like solder or torn metal at either end of it? Maybe find some spring brass and fabricate replacements?

                ---Meltedmetal
                Sorry I was being lazy and didn't post another more useful pic. I was hoping my words would explain that but this will remove all confusion:



                I do agree that a leaf spring is quite possible.

                I may buy the switch just to find out how they solved this and then make my fix for the backup switch.

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                • #9
                  you can get spring stock from https://www.mcmaster.com/ if needed...Bob
                  Bob Wright

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                  • #10
                    Thanks for the better picture. I didn't notice from the first one that they had just put pieces of welding rod in there! And I really get that it is now about just not giving in to the hundred bucks fix. I agree completely; I'd find a way. Just make sure the springs are really strong to provide excellent contact, or you'll end up buying a new switch anyway.

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                    • #11
                      Originally posted by aametalmaster View Post
                      you can get spring stock from https://www.mcmaster.com/ if needed...Bob
                      Thanks.

                      Originally posted by Aeronca41 View Post
                      Thanks for the better picture. I didn't notice from the first one that they had just put pieces of welding rod in there! And I really get that it is now about just not giving in to the hundred bucks fix. I agree completely; I'd find a way. Just make sure the springs are really strong to provide excellent contact, or you'll end up buying a new switch anyway.
                      Yeah. That's where I figured knowing how the actual spring mechanism was designed could be helpful in mimicking it. Welding rod pieces make for poor springs btw

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                      • #12
                        Get a couple feet of piano wire and make a spring.

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                        • #13
                          Originally posted by ryanjones2150 View Post
                          Get a couple feet of piano wire and make a spring.
                          I tried that a bit today. I need to do more refinement of my spring making technique. I would need a small dowel to turn the spring on as the diameter of the spring would need to be 4.5mm max to fit in the slot. I did do a bit of a rig job for the time being. I haven't been able to test it yet.

                          I had an issue when I took the center of the switch out. It looked to me like it should have had 2 ball bearings but it only had one and the spring was tearing up the other side. I used a slightly smaller ball bearing since that was all I could find for now.

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                          • #14
                            Do you think the loading spring(s) was/were supposed to be behind the individual contacts or is the entire contact support assembly supposed to be spring loaded from behind the hub and is supposed to slide on the shaft?

                            ---Meltedmetal
                            ---Meltedmetal

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                            • #15
                              Originally posted by Meltedmetal View Post
                              Do you think the loading spring(s) was/were supposed to be behind the individual contacts or is the entire contact support assembly supposed to be spring loaded from behind the hub and is supposed to slide on the shaft?

                              ---Meltedmetal
                              Interesting way to look at it. I found this picture online that is very low resolution but it seems to confirm the orientation where the slots are facing all the copper on the switch with the contacts in between.



                              Edit: A little bit clearer picture of the 2 position switch where you can make out that the channel faces the other direction.

                              Last edited by jtap; 04-27-2020, 09:03 AM.

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