11/16th Hole

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  • Smokeless
    Junior Member
    • Aug 2015
    • 7

    11/16th Hole

    Hello,

    I am hoping someone can give me a good procedure to drill 11/16th hole in 3/16th box tube. I have a drill press (rigid 5/8 shank), 11/16th split tip drill.

    I am not sure if I should drill series of pilot holes (smaller to larger never had much luck there) or merely center punch and use the 11/16 drill bit. I need the hole on both sides of the tube and am leaning towards going slow with cutting oil.

    Any advice would be appreciated, thanks
  • Captain K
    Senior Member
    • Aug 2015
    • 511

    #2
    I would drill a pilot hole, maybe 7/16", should be a bit bigger than the web in the bigger bit. Use lots of cutting oil. Don't try to turn the bit too slow, 90 feet per minute on the circumference in mild steel with hss bit is recommended, works out to about 525rpm. Use enough pressure to make the bit cut, too little and it will just rub and get hot

    Comment

    • wdtom44
      Senior Member
      • Oct 2014
      • 560

      #3
      I have better luck drilling large holes at slow speeds. There seems to be less chatter at slow speeds. I don't know how slow your drill press will go but I would want to be less than 200 rpm, drill sharp, and enough feed to make a continuous chip. I would start with maybe a 9/64" pilot hole, enlarge to 3/8 or 7/16", then drill to size with the 11/16. Higher rpms may work with rigid setups and machines with constant coolant flow but I find slower speeds work on the typical drill press with a little brush on cutting oil here and there. Thy a test hole in a piece of scrap, see what works for you.

      Comment

      • Black Forest
        Senior Member
        • Jan 2010
        • 8984

        #4
        step drill
        Location: The Black Forest in Germany

        How to become a millionaire: Start out with 10 million and take up machining as a hobby!

        Comment

        • J Tiers
          Senior Member
          • Jan 2004
          • 44281

          #5
          That is a good application for a step drill, even if almost at the limit of size.

          If you use one, drill through at the diameter of the first step first, then use the step drill to go to final size from each side. Some of them do not have 3/16" between steps, though.

          Otherwise, standard technique... pilot hole through, go to final size, drll through but don't hit the feed too heavy, so that it will cut the last bit, instead of popping through and "screwing" through with the remains of the metal as the "nut". Helps to go faster on rpm..... fast rpm and slow feed at the last bit before cutting through.

          If you are worried, you can also put a sacrificial block in the middle.

          Good application for a hole saw, or annular cutter as used with mag drills.
          CNC machines only go through the motions.

          Ideas expressed may be mine, or from anyone else in the universe.
          Not responsible for clerical errors. Or those made by lay people either.
          Number formats and units may be chosen at random depending on what day it is.
          I reserve the right to use a number system with any integer base without prior notice.
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          Comment

          • lakeside53
            Senior Member
            • Nov 2007
            • 10511

            #6
            Lots of techniques can work, but personally I like annular cutters. They will effortlessly cut a beautiful hole.

            Comment

            • Arcane
              Senior Member
              • Oct 2002
              • 4027

              #7
              What's the size of the box tube? What works for a smaller size won't work for a larger size.
              Location: Saskatoon, Saskatchewan, Canada

              Comment

              • J Harp
                Senior Member
                • Apr 2005
                • 719

                #8
                Use a "bullet drill" for a cleaner exit with less burr, and less chance of grabbing and self feeding on breakthrough. Google bullet drill, the link I found is too long, but it shows a writeup by Frank Ford.
                Jim

                Comment

                • macona
                  Senior Member
                  • Aug 2006
                  • 9425

                  #9
                  No need for pilots, especially with a split point drill. Just clamp the piece and set the DO for the lowest speed.

                  Comment

                  • Illinoyance
                    Senior Member
                    • Sep 2015
                    • 1033

                    #10
                    On that thin of material a 2 flute drill will tend too give you a 3 lobed hole whether or not you use a pilot hole. Annular cutters are great.

                    Comment

                    • Smokeless
                      Junior Member
                      • Aug 2015
                      • 7

                      #11
                      Originally posted by Arcane View Post
                      What's the size of the box tube? What works for a smaller size won't work for a larger size.
                      2 1/2 X 2 1/2 X 3/16". Today I was thinking I remember when I had to cut a few 3/8" holes in .250 mounting a boat lift to a dock. We bought some good bits and I do not think we ever got past the first bit. Comes to mind it was about 10 holes.

                      I need to punch these holes through both sides, 8 total. I am just concerned I will get wobble if I step drill the holes with individual bits.

                      thanks for the note

                      Comment

                      • Smokeless
                        Junior Member
                        • Aug 2015
                        • 7

                        #12
                        Originally posted by macona View Post
                        No need for pilots, especially with a split point drill. Just clamp the piece and set the DO for the lowest speed.
                        I have a 135 split point 11/16 manufactured by FMT (China) Black and Gold. My concern is I need to go through both sides of the box tube so the holes need to line up fairly close. Not real precision work but close enough a bolt will go through and the tube can pivot. I will try and post a pic, but I am leaning to using this drill for all 8 hoes. The holes are pretty close to the edge.

                        Thanks to all else, I will reply but kids just walked in, but I thought step drills were for just sheet good not something this thick, but I am learning all the time.....thanks

                        Comment

                        • Andre3127
                          Senior Member
                          • Apr 2016
                          • 458

                          #13
                          On the contrary, I would use a pilot drill SMALLER than the web of the drill. So the web still has some meat to support itself, and not wobble creating a tri-lobe hole. Step bit would be my preferred choice.

                          I don't think a drill press spindle is rigid enough to make a precise hole with a annular cutter. Unless you have a really nice and stout drill press.

                          Comment

                          • goose
                            Senior Member
                            • Jul 2007
                            • 837

                            #14
                            Just clamp the stock in a vise and drill it.
                            Gary


                            Appearance is Everything...

                            Comment

                            • Paul Alciatore
                              Senior Member
                              • May 2002
                              • 17491

                              #15
                              Yes, the step drill is how I would do it. They make a nice, clean hole. And I would use a standard, 1/4" bit through both sides first to be sure the holes on the two sides are aligned. At 11/16" final size you may have to use two sizes of step drills; one to go up to 1/2" and the other to finish it.

                              They do make step drills that have longer steps. I have a couple. And you can go a bit into the next step which will deburr the outer edge. That may get you an extra 1/32" or so in the depth. You can go even deeper on the next step if you don't mind a step on your hole's edge.



                              Originally posted by J Tiers View Post
                              That is a good application for a step drill, even if almost at the limit of size.

                              If you use one, drill through at the diameter of the first step first, then use the step drill to go to final size from each side. Some of them do not have 3/16" between steps, though.

                              Otherwise, standard technique... pilot hole through, go to final size, drll through but don't hit the feed too heavy, so that it will cut the last bit, instead of popping through and "screwing" through with the remains of the metal as the "nut". Helps to go faster on rpm..... fast rpm and slow feed at the last bit before cutting through.

                              If you are worried, you can also put a sacrificial block in the middle.

                              Good application for a hole saw, or annular cutter as used with mag drills.
                              Paul A.
                              s
                              Golden Triangle, SE Texas

                              And if you look REAL close at an analog signal,
                              You will find that it has discrete steps.

                              Comment

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