# Drilling Concrete



## Entropy455 (Feb 4, 2012)

I need to drill 12 holes, each sized 3/4" diameter, and each 6 deep. I'm drilling into some well cured 4000 psi concrete.

I have a 1/3 horsepower hammer drill, and a quality 3/4" masonary bit.

Am I asking for trouble? I.E. should I go ahead and rent an industrial rotatory hammer drill?

And should I drill some smaller holes first, and progress up to my final 3/4" diameter? Or is it best to drill the 3/4" hole from the start?


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## JorgensenSteam (Feb 4, 2012)

I was able to drill some 1/2" dia. holes in 3,000 psi concrete with a typical hand-held hammer drill, but the problem I had was that there are hard spots in concrete, and when you hit a hard spot, you can forget about going any further, and need to shift the hole over to a new position. I used up perhaps 1 bit for every 3 holes or so.
If you try and force your way through a hard spot, you just overheat and ruin the bit.

For a 3/4" dia. hole in 4,000 psi concrete, I think a commercial rental unit will be the only thing that will hold up, unless you only need maybe two or three holes.


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## n4zou (Feb 5, 2012)

No pilot holes in Concrete! They are designed to drill in solid material. Drilling smaller holes first will cause you problems as the drill wanders around in the pilot hole seeking voids or soft pockets hanging up in the process. Have a hose handy so you can flush out the holes as you drill the same as you would remove a drill bit from steel to clean out the shavings and drip in some cutting fluid. Concrete drills like cool water flushes and baths. Don't get the electric drill motor wet! That can lead to a shocking experience. Just set the electric drill on a platform safely away from the drill site, turn on the water and flush out the hole, turn off the water and wait a moment for the water to run off and take the hose off a safe distance before returning to the electric drill and having another go at drilling the hole.


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## tel (Feb 5, 2012)

Might be asking a bit much of a 1/3 hp drill, I'd think nothing less than 1 hp.


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## Jasonb (Feb 5, 2012)

I'd agree with Tel, I would be using my 1000w machine on holes that size. The problem with the smaller drills is not so much the power but the fact they don't have much of a hit on the hamnmer setting and just bounce off the harder bits of aggregate. A slower reving harder hitting drill is what you need.

If its a through hole then a diamond core bit may be easier provided your drill has a safety clutch, don't use in one without unless you want broken wrists.

J


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## Niels Abildgaard (Feb 5, 2012)

Hello Entropy.

What is concrete plus holes destined for?


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## Peter. (Feb 5, 2012)

There are no 'hard spots' or 'soft pockets' in concrete that you have to worry about for your 3/4" holes. 

How well your job goes will depend upon the drill speed and hit rate of your drill as well as the striking force, if you have a light drill which hits so fast it sounds like a missed gear shift then you might have some trouble. Your best option is to just go ahead and try. IF you find it is drilling, but progress is very slow, you might drill a SMALL pilot of up to 5/16" to ease the load on the larger drill but make sure you go no larger than 50% or your larger drill will likely jamb in the pilot hole.


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## Entropy455 (Feb 5, 2012)

Thanks for the responses guys. I think I will go ahead and rent an industrial drill.

Im in the final stages of building my dream garage. Its 40-ft x 60-ft, with 16 foot ceilings. The floor has 60 cubic yards of 4000 psi concrete.

The holes are for installing a car lift. After I get everything put away, Ill take some pictures of the garage and post them.


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## Peter. (Feb 5, 2012)

That would be best. A Hilti TE35-upwards will make easy work of it. I use a TE80 whaich will drill a 2" hole at a push.


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## machinerguy (Feb 25, 2012)

I'm about to drill some 5/8 to mount my lathe. I will lay them out, and start them with a smaller drill ,but only about 1/2" or less deep. Drill through your mounting holes if at all possible. (I can't)
 You will hit hard spots if your concrete has any kind of stone filler. 
 I've removed more concrete than I've installed and found everything from bicycles & fence to pig iron & broken china used as fill and rebar. Unless your house/garage is new, expect the unexpected.
 Expect hard spots.


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## rake60 (Feb 25, 2012)

I remember working in a plant that was moving machinery.

The old maintenance guy comes out with a 1HP hammer drill and a 12" long masonry bit.
I told him the anchors were only 4" long, why such a long bit?

He replied with: 
These floors are 7" thick and we drill to the dirt. 
You can't pull those anchors back out so when they decide to move these machines again, 
we can take a twenty pound hammer and just drive them through until they are flush with the floor.

That 12" long bit makes perfect sense now.

Rick


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## Herbiev (Feb 26, 2012)

Nice workshop . Thats a fraction over 0.055 ACRES.


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## mzetati (Mar 2, 2012)

n4zou  said:
			
		

> No pilot holes in Concrete! They are designed to drill in solid material.



Really?

When I had to drill a coupla 20mm through hole into no less than 8" of concrete floor into one corner of the shop I had the idea of reducing the strain on the drill and operator by starting with a 16mm pilot hole first. 
Then, I chuched the final final size bit, I grasped the drill with two hands, put my weight on it and "Wow! It cuts like butter!!!" Full speed! :big:
Right before reaching the end, it seized. Throwing me myself banging my head on the wall. 
Later, I discovered the second drill was only screwing itself into the hole, rather than enlarging it. A nice quick-helix thread, btw.
Removing it from the pavement took an entire afternoon of patience, iron wires, air hoses, and a few bad words, too.
What worked best was unchucking the motor and tapping (gently) the side of the drill shank: ding!ding!ding! the vibrations helped a lot into discharging the debris.
Only the hardware store bill prevented me from bringing the angle grinder into play.

Marcello


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## Mainer (Mar 2, 2012)

I've had good success with a SMALL pilot hole - 3/16" or so, just enough to relieve the point of the 3/4" drill.

If this is new concrete, you shouldn't have any problems anyway, unless it was made with very hard aggregate.


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