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Drilling sheet metal

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  • Drilling sheet metal

    How do you drill sheet metal so that it doesn't leave nasty looking burr on the other side. I've tried varying the speed and putting MDF on the back but just as the drill breaks through it grabs at the remaining metal and twists it.

    Perhaps I should drill half way through on one side and then drill the rest from the other side, but this doubles the work.


  • #2

    Used to have this same problem drilling aluminum panels for electronic equipment racks. Very soft and would "smear" out the back instead of cutting. That's when I first discovered the joys of 6061 aluminum. Try different tip and rake angles or maybe one of the drill bits made for aluminum. Be sure to clamp the work down safely. Only thing scarier than spinning sheet metal is a power mower.



    • #3
      If you need a really, really clean hole, clamp securely between two metal plates and drill the whole business.

      A center-cutting end mill tends to cut a cleaner hole than a drill, if you have one of the correct diameter. Drill a pilot hole with a regular drill first, then enlarge to final size with the end mill. Needless to say, CLAMP THE WORK DOWN when you're doing this, as the end mill has no self-centering action, at all.

      And as nheng says, a different drill geometry may help. A 135 degree split point drill may work better than the generic 118 degree point drills, for instance. Whatever you use, be sure it's SHARP.

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      • #4
        USE A UNIBIT

        Best thing for sheet metal. Its the stepped-conical drill with one cutting edge.

        They work great, even on thin stuff. The material needs to be thick enough to not twist up like tissue paper. If required, some backup usually deale with that.

        But, compared to a standard drill of any point shape, its 12 times better.


        • #5
          Albert, your half way there with the MDF. Place a piece on the top as well and clamp, making a sandwich. Along with a 135 degree drill angle or a split point drill it should work well. If it still leaves a burr, try sandwiching it between something harder like 1/8" aluminum or steel.

          I use this same process when I make multiple sheet metal patterns... drilling, milling, grinding...

          If it still leaves a small burr, sandwich as above, drill under size and ream to size.



          • #6
            Surprised no one else mentioned this one, ROTO-BROACH. A very neat hole-saw for cutting spot welds. They go from .1875 to .875 diameter in a kit, almost anything else to order. They cut .375 deep for the kit, deeper on order. Money well spent in a machine shop. I use them on stainless, bronze and alum. McMaster Car, MSC, they both have them
            have them


            • #7
              Actually if you hand sharpen a drill bit to a reverse angle leaving a small point in the center it will drill the thinnest of materials with no tearout. Just take your time and don't push it. To sharpen hold the bit into the wheel at say 5 to 10 deg. rotate it and lift up slightly to get clearance. Grind only about 2/3 of the bit and you will end up with a small point in the center. For referance look at a Black&Decker wood bit! Hope I didn't confuse!!


              • #8
                Go with the Rota-Broach. I ued one the other day to drill a 5/16 hole in the bottom of a coffee can. No back-up, No burr Just a sweet round hole. Being brave/stupid I drilled it withour clamping. I held it and my buddy ran the drill press. Rota-Broaches are also known as annular cutters.


                • #9
                  A unibit is the way to go. You can also try what Jim said, sharpening a HSS bit like the bradpopint wood bits but with the end of the spurs higher than the cutting edges, so it will cut like an annular cutter. Make sure the center point is centered and slightly higher than the spurs. Sharpened like that it will cut out a small disc.

                  For small holes I like to use a hand punch and for larger holes a knockout punch. Its hard to center though. If the hole location is too far from the edge to use a hand punch I sometimes use a lead block, a hammer and flat ground pin punch.

                  Drilling sheet metal can be very frustrating. I have sometimes ended up with triangular holes when using a regular drill.
                  Always make sure its clamped down close to where you are drilling so the metal can't flex and try to ride up the bit. I've ruined plenty of work that way. Always use some kind of backup, the harder material the better. This helps prevent grabbing when breaking through and prevents flexing of the sheet downwards under drill pressure, if your DP table has a hole. The best way, as mentioned by previous posts, is to sandwich between two pieces of wood or metal. Problem is that its hard to line up the hole then.

                  Hope this solves your problem.


                  • #10
                    A unibit is absolutely the way to go. I use these at work every day. Nothing better. The only draw back is that your size of hole may be somewhat limited, depends on the unibit that is available to you. Otherwise a holesaw is not bad if the sheet metal is thick enough. There is also a type of hybrid holesaw that has only one carbide tooth, you must go absolutly straight in though, like a drillpress. Not sure what this is called.


                    • #11
                      I don`t know how small you need your holes but hole punches work great in certain circumstances, such as when you are close to an edge! I find them to be much faster and easier than drilling.
                      If you are looking for larger sized holes, posibly you could try using knockout punches. I know you can get them from 1/2 inch size up to where a tin snip can take over, and they do make a nice hole!
                      Location: Saskatoon, Saskatchewan, Canada


                      • #12
                        There's a "butterfly drill" that makes neat round holes when the material is backed up by smooth crap wood. Happy described it well. Wood butchers call the same thing "brad point". The grind is easy to do with a little practice providing you have a good clean corner on your grinding wheel.

                        I have a UniDrill set which I endorse as an excellent drill for thin materials.

                        Another alternative is to drill undersize and taper ream the hole. I have a cheap import set of machine taper reamers I use when I want a round hole of specific size (ever notice how a two flute drill makes a three lobed hole in sheel metal?) in sheet metal or plastic.

                        [This message has been edited by Forrest Addy (edited 10-10-2002).]


                        • #13
                          Thanks everyone. I would have never thought about using unibit. I've alway thought that they are to drill bits what adjustable wrench is to wrench set (in other words not much good). You guys have convinced me otherwise. I'm going to get one tomorrow and try it out.



                          • #14
                            There are specific drills made for bur free drilling of sheet goods - can get them. They are quite expensive and normally only used in high production environments and aerospace.
                            I believe Machinery's handbook has the tip configuration in the twist drill section - it is cheaper to mangle a dozen cobalt twist drills than to buy one of the real McCoy.


                            • #15
                              All of them good ideas you could just pick one and it should work ROTATE, don't feel bad I had the same impression. My tech. school teacher didn't have much good to say about them since they are fairly useless in thick steel. So it took some hands on experience to sell me on uni-bits. Let us know what you use and how you turn out.