I have to drill some half inch holes through 2″ of concrete. I have a hammer drill, but I’m concerned about tearout (or whatever you’d call it for concrete) on the other side. Would using a fast spiral bit w/o the percussion be the best way to get a smooth hole?
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if you need a clean hole on both sides, here is my suggestion. Take and make a pilot hole with a 3/16" or a 1/4" masonry bit. You'll have a little blowout with both, but not much. The slower you go when you are about to go thru the better. While drilling your pilot hole make sure you stay straight both horizontal and vertical. Now take your 2" bit. Start from one side of your wall and drill though 90% of the wall. " use a piece of tape on the bit to show how deep you are. Then go to the other side. Find your pilot hole. Start again to finish. Be careful!! Don't push too hard when the bit is about go thru. The bit could catch and throw you for a loop.
Excellent idea. I'll go with that (BTW, the hole is only 1/2" - the concrete's thickness is 2" - but the principle still applies.)
EDIT Add:
Should I avoid using percussion & stick with just rotary when drilling?
Edited 4/6/2005 12:11 pm ET by Johnny
no, i think you should use the hammer drill. Just remeber to be careful when the final holes hit each other.
If you need perfection appearance wise, go with the diamond hole saw, and cut it wet. If you only need it pretty close, starting the first 1/4" or so from both sides rotary only with the drill will be the way to go. Turn the hammer function on for the middle of the job.
-- J.S.
Diamond hole saw.
Test.
drill all the way with a 3/8 then drill each side with the 1/2