Drilling Concrete

[Leapy]

OK, here's one for the builders amongst us...I'm installing a 12v front-of-the-Land Rover-type recovery winch in the garage to winch the RIB in. I need to drill four holes into the garage concrete floor for rawlbolts that will hold the winch down.

So, using a Bosch 240v 800W drill (set on hammer) and a new Bosch 16mm masonry drill running at or abouts the Bosch recommended 1000rpm I've got exactly...nowhere significant. At best, I've got several holes about 5-10mm deep: I need to get to 60mm for the rawlbolts. The garage floor must be made of recycled industrial diamonds or perhaps harder

What's the professional advice?

[Limey Linda]

1000 rpm sounds awefully fast!!!!. My guess is the drill bit is just skidding.

[PeterR]

Hi,I would imagine you have a high amount of flint/stone in the concrete and your drill is very diy or old and you need a neumatic action and more modern drill.You could try starting with a smaller diameter bit 6mm to act as a pilot hole

[chewy]

Like Pete said make a pilot hole first but most importantly use decent quality bits.

[Leapy]

Originally Posted by Limey Linda

1000 rpm sounds awefully fast!!!!. My guess is the drill bit is just skidding.

Took the speed recommendation straight off the packet the drill came in

[Leapy]

Originally Posted by PeterR

Hi, I would imagine you have a high amount of flint/stone in the concrete and your drill is very diy or old and you need a neumatic action and more modern drill.You could try starting with a smaller diameter bit 6mm to act as a pilot hole

The drill bit is (was) brand new and Bosch branded. I figured the job would be hard - no pun intended - so went for a good quality drill bit.

Thought about pilot holes to build up to the 16mm but a friend recommended against it. I must admit, it seems a sensible way to go.

[Nasher]

As has already been said the 1000rpm sounds a bit too fast to me at that diameter, despite what the packet recommends. I'd be tempted to go with @650rpm.

The Pilot drill should also be the way to go, but to get to 16mm I'd start with a 6mm, then open it up to 10 or 12mm, then finish off with the 16mm.

I had exactly this issue when we moved @10yrs ago, and I needed to bolt my Lathe and Pillar drill down to the floor in my new workshop. Despite having been put down as a normal garage floor by the builders several years before, the concrete slab was really hard. I only needed to go out to 12mm for the holes, but did it in 3 stages.

My Bosch Hammer drill(I think it was 850W) coped well, but I had to change the brushes very soon afterwards. We had however just moved in and Mrs Nasher had me drilling holes all over the place to install stuff.

Nasher.

[Erin]

I bought a pro grade Bosch SDS hammer drill (2-26DRE) http://www.bosch-pt.co.uk/boptocs2-u...object_id=8733 a short while ago and have never looked back. Compared to my dad's bosch 850w diy drill it makes hard concrete seem like cheese and it's actually only 800w. You really cannot imagine the difference it makes until you've try both. My suggestion would be to hire an SDS hammer drill. I think mine is referred to as 3 joule 2kilo type.

[Bigmuz7]

16mm is big for a hand drill .. you dont state the type, so hard to know the specs, 1000 rpm is too fast too If you dont have enough weight to force the bit down, your progress will be minimal.

All these points have been mentioned, as has this,.. drill a pilot hole first but as Nasher says..in two stages, I'd prefer 8, then 12 , then your final, by that time witha 16mm, you'll really feel the torque on your wrists believe me plus you'll probably waste all three drills in the process, cos if its hard stuff they will get hot and not cope, so use water to help with that.. but its the only way for an 800 watt job if is a strong concrete mix ..

If you hit reinforcing inside it, you'll be humped with a masonary bit unless you want to buzz through several best plug the hole and try another spot, or if that fails, time to get a jack hammer out

[Polwart]

Originally Posted by Leapy

Thought about pilot holes to build up to the 16mm but a friend recommended against it. I must admit, it seems a sensible way to go.

simple solution tell your friend to drill the holes (with his tools and bits!)