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Thin stock, lots of holes

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  • Thin stock, lots of holes

    Neophyte questions:

    I need to drill a lot of holes in a 9" x 5" x 1/8" thick aluminum plate.

    27 holes total, 5/8" diameter and tap hole for 10-32. Will probably use an end cutting end mill for the 5/8" holes.

    The plate is the base for a potting fixture for cyclindrical electronic modules.

    I'm assuming the best approach for drilling is to fasten the plate to some backing material and bolt directly to the bed of my mill.


    1. What would be a good choice for this material, plywood, particle board, melamine ????.
    2. I suspect the aluminum plate will want to "curl" afterwards as a result of all the point pressure from the drilling. Any counter measures I can employ? Will a particular backing material help alleviate this?

  • #2
    I'd use particle board. If you can start the holes with a stubby 1/4 inch drill
    bit before using the 5/8 end mill it will go soooo much better. I do the same
    thing on a pair of holes in 0.100 steel as part of a pattern that gets cut out
    later. Depends on how close together the holes are but I don't think it will
    "curl" up much if any if it's 1/8" thick and 6061 matl.


    • #3
      drill press with a brad point drill is how i'd go....manual layout, centre punch and DP is that fastest way to make holes when you don't need .001" accuracy.

      I take that back...partially. still manual layout and drill press but forget the bradpoint. Didn't click how large the dia was and 1/8 is getting too thick for the brad point.....pilot hole and step drill
      Last edited by Mcgyver; 12-16-2012, 01:14 PM.
      in Toronto Ontario - where are you?


      • #4
        carefully lay out and centerpunch your holes and then for goodness sake punch the holes! Or lay the part out in CAD and send it to a waterjet or laserjet shop.


        • #5
          An electricians step drill. They open a hole up in 1/16 inch step from a 1/4" hole.


          • #6
            Melamine is good. It has a pretty consistant thickness.


            • #7
              Your going to thread just the aluminum plate? I'm no electrical guru but just wondering if the one or two threads in the 1/8" plate are going to be enough for those round electrical pot thingies.

              Do you have access to a punch for the holes? Would be fast, easy, and nice clean holes.


              • #8
                Use a uni-bit (step drill) - not one of the cheap Chinese knockoffs. Clean holes, no sheet distortion, and minimal support for 1/8th needed. I'd just have a 2 inch hole in a piece of wood beneath the drill, and move the sheet. Squirt some wd40 onto the bit to stop build-up on the edge. Predrill tip holes - better than using the uni-bit to drill the starting hole if the AL is "gummy". Use a battery hand drill or drill press. Easy stuff.

                You can get Uni-bits in 1/32 increment steps on the smaller sizes, and 1/16 above 1/2".
                Last edited by lakeside53; 12-16-2012, 01:08 PM.


                • #9
                  One more option to threading the aluminum would be to use a press nut (aka: clinch nut). You would drill an oversize hole (about 0.25" as I recall for 10-32), then press the nut in from the back of the plate with an arbor press. They are available in steel or stainless. Check into McMaster.


                  • #10
                    10-32 in 1/8 gives 4 threads. Plenty strong for most uses of #10 screw. In 1/8 AL drill the tap hole, mount a taper point tap in a battery drill and tap in one pass on the L speed range.
                    Last edited by lakeside53; 12-16-2012, 01:09 PM.


                    • #11
                      If I was doing this, I would use a 5/8" Rota-Broach and a combination drill-tap. This would create the fewest tool changes.


                      • #12
                        Originally posted by vpt View Post
                        Your going to thread just the aluminum plate? I'm no electrical guru but just wondering if the one or two threads in the 1/8" plate are going to be enough for those round electrical pot thingies.
                        Wow, thanks for all the good suggestions, so quickly!

                        I thought someone would bring up the 10-32 threads in the 1/8" plate question!

                        All the 10-32 screws will only be finger tight, and serve to hold a "top-plate" in place just to keep the mutiple cylindrical potting forms from falling over while curing. So the lack of threads isn't significant.

                        The 5/8" through hole diameter is not critical but the more square, and distortion free, the better to form a better seal and keep the potting epoxy from leaking out of the form due to gravity. I may need an o-ring here. Although I love and use Uni-bits frequently, I think a 5/8" center cutting end-mill is the best choice here. Although a water jet operation is intriguing!

                        There is a couple of top plates required for the fixture, one to keep the cylindrical forms from falling over, and another to accurately suspend some additional hardware within the form, and within the pot. I need good registration across all three plates, so I need to do this on my mill drill (with a new DRO) for accurate location, as opposed to my drill press.

                        The backing plate material I was thinking of, but couldn't remember, when I made the original post is called "MDF" (medium density fibreboard) and is available at Home Depot. It's flat and will hold a wood screw thread good for attaching the alum plate.
                        Last edited by jmarkwolf; 12-16-2012, 03:07 PM.


                        • #13
                          If it were me, I would rough out the 5/8" hole with a 1/2" first, then come back and hit them all with the 5/8" end mill.
                          It has been my experience that you will get a cleaner more uniform sized hole in doing this.


                          • #14
                            If you really want them round, rough drill as suggested above then single-point bore them.


                            • #15

                              MDF makes a great backer as long as you don't use coolant. Very accurate in thickness.