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Accurately drilling concrete

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  • Accurately drilling concrete

    Any tips on how to drill holes in concrete pretty much where I mean to? Here's the details... I have this vise stand with four mounting holes on the base plate for fixing to the floor. I previously had this in the garage, and when I put it there it was a disaster. I marked with a sharpie, drilled the holes and installed the lag anchors. I go to screw it down and two of the four are waaaay off. I ended up having to drill out two new holes for two new lag anchors and patching the previous. This is not a new experience for me in trying to mount anchors into concrete.

    The vise stand has been re-delegated to the basement. I mark out the four holes. I install two anchors (they're the female threaded, expanding plug type). So far so good. Put the vise stand over the two, and they're good. BUT the other two are way off. Good thing I remembered last time

    I'm using a 1/2" hand-held hammer drill with a 5/8" masonry bit. With all the 'hammering' going on, it's all I can do to not have it wander. Before I screw up my basement floor some more (I have experience in that ), is my best bet to drill undersize with a masonry bit while the vise stand is in place? For some reason, I expect that to make the larger bit wander off even more or go oversize---which will ruin the whole trick with these expanding anchors.

    Thoughts for this poor fool?

  • #2
    Maybe you should use a optical punch
    Just a thought but can't you drill the size hole you need in a scrap piece of metal or wood and use it as a Jig to stop the wandering.

    Just weight the jig down or even better step on it with both feet and drill between your feet.
    Not really OSHA advice but hey "Man dismembered by hand drill" is not really a headline you will see in the paper ......yet

    Last edited by Westline; 06-01-2011, 07:22 PM.
    If you are using violence and it does not work, You are not using enough or it is upside down.
    You can always just EDM it...


    • #3
      I'd probably use a star drill and hammer to get the holes started (after one initial hole is drilled), maybe a 1/2" or so deep. which should keep the rotary drill from wandering. Or at least not as much wandering.
      Lynn (Huntsville, AL)


      • #4
        Make a template , 2x4s or something, drill accurately and then glue it to the floor with silicone or something you can peel off with a shovel.
        I've never tried it, but it might work.
        Tom C
        ... nice weather eh?


        • #5
          Originally posted by Westline
          ... drill the size hole you need in a scrap piece of metal and use it as a Jig to stop the wandering.
          Even easier:
          Use a piece of plywood for a jig.

          Even easier yet?
          Use the original base plate for your jig. Drill one hole about where you need it (at this point, you could probably just drill one an inch or two away from the ones you've already drilled). Then install the anchor and bolt the stand down with just the one bolt. Then drill one more using the base plate as the guide jig, install anchor and bolt that one down. Now you have two holding it tightly in place so you can drill whatever remains, continuing to use the base plate as the guide jig, and they'll all be correctly located.
          It also wouldn't hurt if you were careful to keep the drill as plumb as you can while drilling so the anchors don't all stick out at different angles.


          • #6
            Use a jig, as others have recommended, but make the holes SMALL, as in maybe 1/4". A small bit won't want to wander as much. Start the hole for an inch or so, then switch to the larger bit. You could even use the actual part to be bolted down if you made some bushings to drop into the mounting holes.

            FWIW: I prefer the "Red Head" style anchors over the lead sleeves. I've also turned up some sleeves from steel, drilled & tapped, knurled on the outside. Glued them into the floor with JB Weld. This allows me to remove the device and plug the holes with some round-headed bolts. I made the sleeves from 1/2" rod, D&T'd 5/16-18. It holds my Dillon loading press.


            • #7
              I'd suggest starting with a smaller bit and open it out from there. It's now pretty much the way I always drill larger anchors these days if I want them relatively precise or the starting surface is uneven. It's easier to keep a small bit aligned and with the bits used on rotary-impacts changing them takes only a second. It's also much easier on everything if you don't try to immediately pound away with a big bit just because it's a powerful machine. In other words precisely the same principle as if you were drilling a hole in steel. By using a small bit to begin with often I won't even drag out my rotary-impact and will simply use a standard impact drill; much lighter and can be used one handed if required. My rotary-impact is relatively heavy and VERY loud ... by heck they drill concrete though!

              Of course that's assuming you calibrated your sharpie before use


              Edit: Ah I see the poster above beat me to it. Ok ... what he said!
              Last edited by PeteF; 06-01-2011, 07:41 PM.


              • #8
                Drilling concrete

                Make a template out of 1/2" steel plate with holes the size of your concrete drill bit. Drill one hole, put in an anchor and bolt the plate down. Drill the opposite corner through the template. Unbolt, put another anchor and bolt the template with 2 bolts. Drill the other 2 holes a couple inches deep, take off the template and finish those 2 to depth. Then all the holes will be spot on. Edit to add: Tyrone beat me to it while I was typing.
                Last edited by Toolguy; 06-01-2011, 07:37 PM.
                Kansas City area


                • #9
                  jdunmyer, I actually think we're talking about the same style. These are just threaded plugs--when you remove the bolt, it is flush with the floor. I did that in the garage so I could remove it and screw some set-screws in flush during the winter when the car is there. You expand the plug by screwing in the screw which pushes an expander in the bottom of the bore.

                  In any case, the actual base holes are smaller than the drill. Looks like I will keep it in-situ with the two already done bolted down. Make a plug and do a 1/4" pilot. That made sense to me. A 1/4" is small enough that it won't mess up the final hole size when I go back with the 5/8" bit.

                  Thanks for the suggestions! They're appreciated.


                  • #10
                    I like the wedge type fasteners. The advantage is that you don't drill an oversize hole. Just use your piece as a template, and hammer the anchors right in. I would do one, secure it, and drill the others. Just make sure that the hole is deep enough, and that you don't have dust packed in the bottom.


                    • #11
                      Extraneous pictures just for the heck of it. Two holes drilled; two to go.

                      Garage. You can see the original goof on the two bottom holes. With setscrews installed.


                      • #12
                        I would attack it with a chisel.. To turn the sharpie marks into a nice starting divots. And because im an impaitent man, that chisel would likey be attached to an air hammer..

                        Once did that on some cement that was... in the way of a wall I was installing, just a tiny bit of cement that was too high.... Only took me about 30 seconds to realise using an air hammer would be faster and more fun then a regular hammer :P But in your case a regular hammer might do the job better, as its more controlable, and you don't need to remove much to make a good starting divot for your drill.

                        (alternatively, start with the air hammer on its LOWEST setting, and crank it higher after a small test usage untill it does the job. this will allow you to have all the finesse of a skilled scupture, With none of the repeative stress injury of a thousand hammer swings. Air hammers on low settings are VERY easy to control tools!)
                        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


                        • #13
                          Do it per shewlaces instructions. The aggregate, particularly if it is very hard will cause the bit to walk. You cannot control this with a hand held drill.

                          To be redundant - Drill the first hole and fasten the base plate down. Using the base plate as a template drill the second hole. Fasten it. Then drill the remaining holes. The base plate will keep the bit from walking off if it hits hard aggregate.

                          The other and more expensive way is to use a diamond core bit.


                          • #14
                            Originally posted by FETOAU
                            The other and more expensive way is to use a diamond core bit.
                            You use a diamond core bit to drill a 5/8th hole with a dry rotary impact drill in concrete?

                            We must have very soft aggregate here, as I said I have absolutely no problems simply by drilling with a smaller bit first. Especially in a scenario as described where you just have to drill straight down and not overhead. Mind you I do keep my masonry bits sharp, and that's possibly another tip I can offer as that definitely makes a diference.

                            Last edited by PeteF; 06-01-2011, 10:26 PM.


                            • #15
                              I usually start with a small pilot hole. Draw some large cross marks at each location so you can still see your intended location after the big drill is started. If it starts to go off center you can steer it a bit until it is pretty deep.
                              Don Young