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  • Fish Plate Welds???

    So I decided to cut the frame of my project truck to make it a short wheelbase. I cut the frame, welded it back together and then make some fish plates to put on the inside of the frame. This is a 1985 Chevy 1 ton 4x4 frame (1/4" thick). I Welded the plates on thought i did good. Few days later I was looking at the roll cage of my Dozer at work and seen that on those fish plates the ran the weld bead about an inch past the plate and flared it outward away from the plate. Why is this? also I did not do this, should I? Can I(now that i have already stopped the bead of weld)? any insight would be greatly appreicated. Thanks, Pat.
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  • #2
    Hopefully you didn't do a straight cut on your shortened frame, you should use a "Z" cut which is significantly better. Can't help on the fish plate? I've seen that somewhere recently but didn't understand the reasoning behind it.
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    • #3
      Originally posted by nocheepgas View Post
      I've seen that somewhere recently but didn't understand the reasoning behind it.
      This is probably the thread where you noticed it: http://www.millerwelds.com/resources...05&postcount=1

      The first picture is exactly what you are talking about.

      Although I have never dealt with such a repair, I believe it is to reduce the chance of a stress related crack forming from the very corner of the gusset. As for if you can add that bit of weld after... that I don't know, sorry I couldn't be of more help.
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      • #4
        Where I work it is called a "tail out". I don't know if this is a regular trade term or just what they call it at our shop. I have seen it done on man lift booms, boom trucks, and cranes that I have operated but I never did it myself until I started working at my current job.

        I am under the impression that it helps to prevent cracking by having the weld terminate out of line with the main weld. Like in the pictures in the link, the fillet weld runs past the end of the fishplate then curls away from the line of the weld.

        I don't know if cracking is what it prevents, but thatís my guess. We have a welding engineer that specifies stuff like that. I thought about asking him what it's for when I first saw it on a print, but when he starts talking about welding he makes my eyeballs hurt.

        If you want to add them to your truck frame splice, they will work best if you grind your welds back an inch or so. Just adding a tail out to the end of your weld won't be as effective as having the weld tail out merge into the original weld 1 or 2 inches past the end of the fishplate.



        http://www.millerwelds.com/resources...05&postcount=1
        Attached Files
        Will

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        • #5
          It isn't something I would lose sleep over, you shortened the frame which by nature will reduce load. How hard and long will you run this thing? Lot of equipment is under continuous use, high stress, abuse.

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          • #6
            Tail outs

            Seen them on excavator booms 2. My impression is they reduce stress risers at the corners of the doublers. I think they probably do work - Never seen one crack before! Most of the ones I've seen are feathered out flush at the ends with the original base material. They are all factory welds?

            Usually like 6" long and curved with a lot of attention to how they are feathered at the ends?
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            • #7
              "runoff" ,"tail" or "pigtail" (depends on the angle it runs off at and who welded it). Main purpose is the prevent a stress concentration/stress riser at the point of a diamond/fishmouth/square scab and reduce the chance of a crack forming at that point. Whenever I see it done I always think to myself "nice touch" because not many people are aware of the stress concentrations that an abrupt transition point will produce.
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              • #8
                Originally posted by MR.57 View Post
                "runoff" ,"tail" or "pigtail" (depends on the angle it runs off at and who welded it). Main purpose is the prevent a stress concentration/stress riser at the point of a diamond/fishmouth/square scab and reduce the chance of a crack forming at that point. Whenever I see it done I always think to myself "nice touch" because not many people are aware of the stress concentrations that an abrupt transition point will produce.
                Hmmmm.....the "runout" prevents a perpendicular crack along the flang, tube, plate or whatever you are fishplating. If you wrap the weld completely the HAZ can cause the base material to crack across thus possibly breaking......usually with a "runout" just the weld will crack near where it meets the fishplate IF too much stress is placed upon the piece. I have repaired several "runout" welds but I have never seen one go into the base metal. Dave

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                • #9
                  why inside

                  i have 2 of those things sitting out in the yard 1 a cucv 1 ton the other 1/2 ton, i chopped them both, i make a simple straight cut, weld the frame back together and then plate the out side of the frame, are you building some thing to show, is that why you hid the fish plate, just curious

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                  • #10
                    If you use the z pattern, I dont think you would need a fishplate.A couple of flat bar on the inside flange welded length wise only not all around for added safety wouldn't hurt.
                    But if you fishplated like the diamond pattern and welded them all around I dont think they would get stressed enough. Just keep and eye on them when ever you go 4wheeling and do those big jumps

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                    • #11
                      down here, we call them "cat tails" and its exactly as described earlier. it terminates the weld at a place different than the main weld, diffusing stress risers. a crack will almost always form at the end of a weld or at sharp corners. cutting rosettes into the scab plate and plug welding them will also help alot for strength as well.
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                      • #12
                        Thanks to everyone for their input on this matter... i've gathered im not going to lose sleep over it and just run it. i plan on bolting the plates in place as well due to a cross member thats going there as well. i think it'll be just fine. Thanks again, Pat
                        Millermatic 180w/autoset
                        Spoolmate 100
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                        • #13
                          every body gets very technical on this issue but some thing hardly ever get mentioned is, what material to use, thick, thin??????????????? or the same size as the frame is made of, that is to me far more important than the way the splice is done, ive seen guys use 1/4 plate an a jeep to guys using gym lockers on their frames, just a thought

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                          • #14
                            Originally posted by kevin View Post
                            every body gets very technical on this issue but some thing hardly ever get mentioned is, what material to use, thick, thin??????????????? or the same size as the frame is made of, that is to me far more important than the way the splice is done, ive seen guys use 1/4 plate an a jeep to guys using gym lockers on their frames, just a thought
                            I was just wondering the same thing, What is the rule of thumb for determining the thickness of the reinforcement plate? Mike

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                            • #15
                              Rule of thumb is you use the same material and the same thickness or less,
                              Never use thicker material as it makes the fishplate stiffer then what you're putting it not a good idea.
                              The fishplate has to move with the material you putting it on and not work against it.
                              Hope this help.

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