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    I have intermittent need to make square holes and slots in .040 aluminum boxes. These are in pre-made boxes. The square holes and slots sizes needed are:

    1.75" round
    .5 x 1.5
    .675 x .50
    .5 x .375

    I have been drilling them out mostly and hand filing to dimension. Since it seems I will need to continue this intermittent job for a long time, I want to speed this part of the job up a couple of notches.

    Best recommendation while not breaking the bank ??

    Work holding seems to be a problem in the mill. The Al. is that soft "gummy" type too.

    Thanks !

  • #2
    A hand nibbler would speed up the rectangular holes and a knockout punch would make the round hole.

    You may want to print and photocopy an overlay, glue it on, drill pilot holes, then cut to the lines.


    • #3
      You may actually be able to find greenlee knockout punches for those dimensions.

      Check an electrical supply company like Newark.



      • #4
        A round punch for that size is simple to make for that material. Some mild steel bar stock will do the job. To cut the punch cutting end to shape chuck it up in a four jaw perpendicular off the centerline and do a slow interrupted cut on the business end. It will make a perfect cutting shape. You might want to case harden it afterwards. This has worked well for me.

        For the orthogonal holes I would be tempted to try making some punches for them too. You will need to weld up the female end to match the die. I'm not sure how well this would work, I haven't tried it.
        Free software for calculating bolt circles and similar: Click Here


        • #5

          I looked at Greenlee, they do have the sizes I need, but they are expensive !
          I suppose I can make something of a punch in the shop. I doubt it will be as good, but it may do the job.
          There are a lot of Greenlee products on E-bay I noticed too. I may have to lurk around there for the size I need.
          A flycutter in the drill press does do the job nicely for the larger round holes, even if it is a little scary.



          • #6
            I posted a question like this a while back and got some really good info. The subject line was "Greenlee-type Punches?". Check out the archives - a user named J Tiers replied with info about a punch he made - like a Greenlee, but better.

            The curse of having precise measuring tools is being able to actually see how imperfect everything is.


            • #7
              Please explain your punch making tip. What is off center and what would the shape be when cut? Thanks--Mike.


              • #8

                I went and looked at that thread. Thanks for pointing it out. I may just try something like that. I think I'll find a cheap greenlee punch on ebay, just to figure out how it is suppose to work. From there I can likely make what I need.



                • #9
                  I've made similar (round) punches for ali. Oil hardening silver steel, AKA drill rod. Just hardened the tip of the rod then hollow ground it on the bench grinder.
                  Rgds, Lin