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Will welding distort tapped holes?

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  • Will welding distort tapped holes?

    I have a 5" wide by 20" long x1/2" thick mild steel plate. This plate will have numerous 3/8" holes drilled and tapped. Holes will be 3.75" center to center in the 5" dimension. These will serve as potential pillow block mounting locations. This leaves about 5/8" from the holes center to the edge of the plate. This 5" x20" plate will be welded to a larger 1/2" mild steel plate.

    I was going to drill all the holes and tap PRIOR to welding but then just had an ugly thought. Could the welding AFTER all the drilling/tapping distort the holes so that they would be unusable? It would be much easier for me to go with plan A of drilling and tapping all of the holes prior to welding. I would not be able to drill all the holes I wanted if I have to drill after the welding.

    Am I good to go with drilling and tapping prior to welding? I greatly appreciate your help and potentially saving we from a cluster. Thank in advance.
    Last edited by PT Doc; 12-28-2013, 11:47 PM.

  • #2
    Sorry to nit pick but in the dimensions you give, how thick is the first plate, the one you would be putting the holes in?

    Asking as it is written as 1-2" thick...did you mean 1/2"? as that matches the thickness of the plate you intend to weld this one to...

    Not an expert but that thickness dimension, to me, would certainly change my thoughts/answer.


    • #3
      corrected original post to 1/2" thick.

      I guess another option would be to have the 3/8" screws in the holes while the plates are being welded. Thanks for the help.


      • #4
        The "Tool and Die Guy" has this recent vid regarding cold rolled. In his case he was creating cutouts, not holes, but it does show what can go wrong.

        Any pre-drilled holes in his work would have moved with the work.


        • #5
          Drill and tap away and then after welding run a tap back through the holes and wipe out any distortion present before installing bolts in them.I fabricate stuff with tapped holes all the time and it's SOP to re-run the threads before use if there is a chance of a problem.
          I just need one more tool,just one!


          • #6
            I agree 100% with weirdscience , as I often have to fabricate or replace pieces with tapped holes when repairing machines.
            More often the tap will clear any spatter from welding , those little balls of hot metal can get into strange places.


            • #7
              Thanks for the help.


              • #8
                Do a lot of welding and never had a problem with the welding messing up tapped holes via distortion (unless you are closer to the hole edge than its diameter), but as posted you can get splatter in all sorts of spots. I either plug the hole with a bolt or tap over it when welding (unless its close). Will use a tap to clean the hole if I have to, but work hardened spots are not kind to tap teeth, especially small ones.