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  • Drill holes in granite?

    I need to drill some holes in a piece of granite about 3/4" thick.
    What's the best tool for this?
    Carbide, HSS, hole saw or something else I can easily obtain and power?
    I need 4 holes for 1/2" bolts.
    I have a hammer drill and a set of carbide tipped drills that I use on concrete but that doesn't seem like the correct tool.
    First time I have tried this and have no idea how to proceed.
    Bill
    I cut it off twice and it's still too short!

  • #2
    https://www.amazon.com/dp/B06XW9C44P...a-350598468123

    sam

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    • #3
      Hollow diamond drill worked for me. Continuous flush with water or build a clay dam around the hole and fill with water. They're not very expensive.

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      • #4
        For that thin I'd go with the hollow diamond bits. Keep the bit around after for doing holes in glass or other similar rocky materials.

        The hollow diamond bits also do a great job in concrete. Just use more water as the matrix cuts faster and will mud up and clog more easily.

        To ensure a good flushing at the diamonds be sure you "clear" the end by pulling back and forth fairly frequently. Like push for no more than 5 seconds or about 1/32" (whichever occurs first) worth of movement then pump the drill back and forth in the hole a couple of times to flush the cutting face. You'll cry if you let it mud up and catch. The drill will still turn but you won't be able to pull it back out through the schmoo that cakes up on the walls behind the diamond front.

        If the bit isn't long enough to go all the way through you can drill down to around 1/2" then with a screwdriver reach in and snap off the core then carry on through. Don't get closer to the far side than about 1/4" before you do this or it may spall out the surface on the far side.
        Chilliwack BC, Canada

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        • #5
          Simpler yet, a length of tubing of the appropriate size and some lapping compound, clay, and water.

          Build a little dam around the location of the hole with the clay to contain the water and the lapping compound. Put the tube in the drill press chuck, the hole might have been aligned before, spread lapping compound on the circumference of the hole. Put moderate pressure with moderate speed, flood with water to help the recirculation of the grit in the compound, let the abrasive do the work. It goes fairly fast.

          Ok, it might not be simpler but it is cheap, you can drill as many holes as you want, the bit won't become dull!

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          • #6
            I also would go for the diamond, not using hammer reduces the risk of cracking the granite.

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            • #7
              I used a masonry drill when I put holes through a three inch thick granite surface plate. Sacrilege, I know. I also used a garden hose to supply a steady stream of water.

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              • #8
                I was going to suggest a hammer drill as well. But then I noticed the 3/4" thickness. Didn't figure that would be too wise for THIS case.
                Chilliwack BC, Canada

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                • #9
                  Hammer drill may work if you drill from both sides and meet in the middle. Go gently.
                  Probably not good to have a pilot hole.

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                  • #10
                    Don't hammer drill it.
                    As stated the diamond coated hole saws readily available work well with patience, and flood. I drilled through a 5" granite plate with one via drill press, and many though a concrete slab with a hand drill. Getting them started can be tricky if using a hand drill, as they want to 'skate' (no pilot). I set up a couple of stubs of 4x4's so I had a 90 degree corner to rest the drill into to keep things perpendicular.. once the cut starts, there's no issue. Brace the back of the cut to minimize blowout.

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                    • #11
                      Originally posted by softtail View Post
                      Don't hammer drill it.
                      As stated the diamond coated hole saws readily available work well with patience, and flood. I drilled through a 5" granite plate with one via drill press, and many though a concrete slab with a hand drill. Getting them started can be tricky if using a hand drill, as they want to 'skate' (no pilot). I set up a couple of stubs of 4x4's so I had a 90 degree corner to rest the drill into to keep things perpendicular.. once the cut starts, there's no issue. Brace the back of the cut to minimize blowout.
                      They also have hole saw guides like this
                      https://www.amazon.com/Adjustable-Ho.../dp/B000NB72P2
                      https://www.amazon.com/DRILAX-Fixtur...RWKJQ0GWP03AG9

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                      • #12
                        Thanks for all the replies.
                        It looks like "diamond" hole saws are the way to go.
                        I had no idea they were so cheap. Less than 15 bucks for several sizes.
                        I know they can't be real diamond. I wonder what the material really is?
                        Bill
                        I cut it off twice and it's still too short!

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                        • #13
                          Synthetic diamonds mostly produced in an autoclave type environment. Diamond drills used to be natural diamond but advances mean that they can control the size, shape and density more closely by using synthetic. Some diamond core bit segments even contain diamonds set in a geometric symmetrical pattern. I'd like to know how they achieve that.
                          Peter - novice home machinist, modern motorcycle enthusiast.

                          Denford Viceroy 280 Synchro (11 x 24)
                          Herbert 0V adapted to R8 by 'Sir John'.
                          Monarch 10EE 1942

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                          • #14
                            Even if natural diamonds are used, industrial diamonds are far cheaper than those used for jewelry, especially in small particles as used for abrasive in this case.

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                            • #15
                              i've drilled lots of holes in granite surface plates with regular hardware store masonry bits - no problema on the drill press, running dry.
                              Cheers,

                              Frank Ford
                              HomeShopTech

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