Drilling a 6 in hole through 4 in thick concrete

[Paddy]

I have a concrete house and had to drill quite a few holes over time. I have a commercial grade splined shaft hammer drill. Bits from 1/2 in to 1 in

I can drill holes quite fast, so that's not the issue. In the past I would drill the circumference and then the long process of drilling diagonally to cut the webbing between the holes. Placing the holes to close and the drill just jumps into the hole next to it. Too far away and you get a thick web.

Ideally yo would leave about an 1/8 in of web. Even in the perfect world, getting the chunk is very difficult. So I thought there might be some tricks out there.....

Do as above but then drill a pie shape pc out? then keep expanding? Or start in the middle?

 

[groundcover]

Archer USA 6 in. Diamond Core Drill Bit with V-Tip for Concrete Drilling VB600 - The Home Depot

The 6 in. Diamond core drill bit with V-Tip for concrete drilling by Archer PRO delivers high performance and long life at affordable prices. This core drill bit is optimized for a wide range of construction

www.homedepot.com

 

[oldnslo]

I have used core drill like above but I believe they require a special drill to operate properly. The one I rented had connection for putting water in the center of the drill so it forces tailings out from under the bit. Make a nice clean hole vs the drill small holes and try to chip out the center.

 

[grsthegreat]

Ya, you can rent a core drill machine. It has to bolt to either the ground or wall to use. Uses water

 

[Paddy]

I'm drilling through a concrete roof with 4 in of foam/OSB/roof rubber on top.

So back to my question, what drill pattern works best?

 

[grsthegreat]

There is no easy way to do it. I simply drill as many small holes as close as you can then demo . Lots of cleanup of webbing needed doing it this way. Ive done it up to 4 “ myself, and it sucks. Drill always jumps holes

 

[ponytug]

There is no easy way to do it. I simply drill as many small holes as close as you can then demo . Lots of cleanup of webbing needed doing it this way. Ive done it up to 4 “ myself, and it sucks. Drill always jumps holes

I agree. BTDT.

These days, if it were me, I would rent the wet core drill for just the one. If you think you are going to do a few, but not zillions, there are cheap ones available on line. Not Hitachi quality, but many of them will get the jobs done.

Not recommending this one in particular, but just to give you an idea of the cost. This would need some chains and clamps to hold it in place, plus the 6" drill.

https://www.amazon.com/Happybuy-Diamond-Drilling-Capacity-Concrete/dp/B07B9TVF6B

or better
https://www.amazon.com/dp/B08JG1KVX4/

Figure another $130 for a 6" wet core drill...

All the best,

Peter

 

[Egon]

Is there rebar involved?

For four inch concrete a dry core bit may be the easiest.

 

[EddieWalker]

I use a 1/2 inch SDS Max bit for drilling large holes through concrete slabs. I've never had a problem with the bit wanting to go into the hole next to it, but I might be spacing my holes farther apart then you are. I think the half inch bit is perfect for this because of how quickly it goes through the concrete. I also have a SDS drill for smaller stuff, but it really doesn't compare to how quickly the SDS Max is. What type of drill are you using?

 

[LittleBittyBigJohn]

I'm for renting a core drill. If not that then: Draw a circle with the diameter you want on the centerline of the drill bit, mark a drill location then move drill dia+web thickness you want and mark again. It's not going to be fun any way you do it with the multiple drill hole process. But, it shouldn't be super terrible. Decide if you want to have a chewed up looking hole with the inner dia you want large enough to not have to grind the webbing, or if you want to make the hole smooth without webbing and have to grind it out for fit. If the 2nd, rent a core drill.

I've done both. If you just need a hole, multiple drills then hammer out the slug is fine. But, regardless how well you make your layout template, it's going to look like a dog chewed it out. Hammerdrilling concrete is not precision work. Your bit is going to walk and at least one of the holes is not going to be plumb.