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Squaring a small blind hole

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  • Squaring a small blind hole

    I have to build a new latch for my dive camera enclosure. I screwed up and forced it when I should not have.

    The latch has three blind cuts in that I will cut all the way through but it left a question of how would I do this.

    The blind hole is 1/8"X1/2"x1/8 deep with squared corners. Is there a way of cutting the bottom corners? If I was working with wood I would grab a sharp chisel and go to tapping.

    My plan is to replace the POS plastic with stainless steel. This will allow me to cut all the way though and file the round to square.

    Just asking to learn.

  • #2
    Pics would help

    Sent from my iPad using Tapatalk


    • #3
      I have a hand forged cape chisel that might work for you. It has a narrow blade but I haven't checked the width. I could loan it to you if you pick up the postage both ways.


      • #4
        I would either make it in two parts, broaching the square hole in one and welding the two together to create the blind square hole, or I'd mill a hole, make a round piece to press in, and broach the square hole in that round piece.

        Or find a guy with an EDM.



        • #5
          Both are very good thoughts!

          EDM Can I make one of those???? hahahahaha


          • #6
            Originally posted by metalmagpie View Post
            I would either make it in two parts,

            Im with magpie. make a weldment. Do you TIG weld? It can bee a brazed part also. JR


            • #7
              Use a wood chisel on aluminum, and maybe a dremel. Be easier than stainless


              • #8
                Here's another approach that works really well - neat and accurate. Take a piece of material and mill a slot in it such that the width and dept equal the sides of the square's . Silver solder, braze, weld or if its a light enough app even soft solder a piece forming a cap over the slot. Take to the lathe and turn the outside round. You now have an "insert" with round outside and square hole - use retaining compound or braze it into the corresponding round hole in the work.

                edit - On reading the thread, I suppose its close to or the same as metalmagpies suggestion
                in Toronto Ontario - where are you?


                • #9
                  Wobble broach in the mill spindle. I made my own for the lathe, but one popped up on ebay for the right (low) price for a commercial one for my mill so now I can make any blind holes the shape I want with a little grinding of a new broach insert.


                  • #10
                    A quick and dirty solution that might work, depending on application, is to drill out the corners. Example image at the link below:



                    • #11
                      Thank you for the offer for the forged cape chisel. Time is short as I am leaving next week to dive.

                      I would buy the part but it is back order... story of my life. I would have started on this but I am pull 12 hour shifts and working in the shop would lead to other problems.

                      TIG... I like that thought!!! Cut up the part like a Tetris game, leaving square hole where I need them. Stack up the parts, and long part for the arm part. TIG it and the shape the out side of it on the sander. For this project, I will leave the holes all the way through. The old part was plastic, this being stainless, I am not as worried about it letting go again.
                      I will try to get some photos loaded. Only because I like seeing other peoples photos of projects.

                      Fasttrack--That is the best I have seen for cutting the blind square hole. This also would address the stress point of the corners and stop it from cracking.



                      • #12
                        I assume you don't have a rotary broach. Otherwise, you wouldn't ask the question.

                        P.S. Just noticed Mr.Fluffy mentioning this tool.
                        Last edited by MichaelP; 11-04-2017, 12:17 PM.
                        WI/IL border, USA


                        • #13
                          The simplest approach, if you can tolerate rounded ends is just to mill the slot slightly longer than the original.


                          • #14
                            Originally posted by Illinoyance View Post
                            The simplest approach, if you can tolerate rounded ends is just to mill the slot slightly longer than the original.

                            That is what I ended up doing.