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I'm using an 18v makita hammer drill with a 3/16" Bosch blue granite turbo concrete bit to drill 2" deep holes into concrete-filled cinder blocks. With a fresh bit, it takes about 15 seconds to drill a hole. By the 4th hole, it slows to a crawl and it takes 2-3 minutes to drill a complete hole. After the 5th hole, the bit is completely shot and I have to get a new bit. I've gone through half a dozen bits now, trying to discover what I'm doing wrong - and I have no idea.

The hammering action of the drill isn't activating, so i'm losing all of the impact potential - I can't really apply any more force than I am already, as the drilling is happening over-head at an awkward angle... Any idea if there's a reason the bits dull so quickly? Is this a better job for an impact drill?

I should also say that I can't notice any visible difference on the tip of the bit - it doesn't look blunted, or marred, which is part of why it's so puzzling. I don't have a means to sharpen it, but just from visual inspection it looks OK

T.J.L.
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Tyler M
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5 Answers5

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The hammering action of the drill isn't activating

So the bit is overheating due to friction. It is supposed to hammer the material you're drilling into dust then evacuate it, not rub it off through friction.

You have to activate the hammer action.

Pretty much the only use cases for not using the hammer action are when drilling into ceramic tile to avoid breaking it, or drilling into plasterboard or other soft materials where hammering will smash through and make a crater on the other side...

Is this a better job for an impact drill?

Advantages of cordless hammer drill's are

  1. Light weight.

  2. Convenience, you can drill the hole and drive the screw with the same tool.

  3. It works for a few small holes (like less than 6mm diameter) in easy to drill materials like brick, cinderblock, soft stone (limestone), etc.

Drawbacks: noisy and underpowered, slow/useless on tough materials (hard stone, concrete especially if it contains rebar).

If you want to make lots of holes, or diameters like 10mm and up, or drill into tough stuff, a rotary hammer with SDS+ bits will be a LOT faster.

Don't get an impact driver for drilling, impact drivers are for bolts and tough screws, not for drilling.

I don't have a means to sharpen it, but just from visual inspection it looks OK

It's tungsten carbide, you can't really sharpen it. Besides, it doesn't need to be really sharp, it's basically a tiny hammer with a blunt point.

Giacomo1968
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bobflux
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An SDS-plus hammer drill will make holes very fast using a bit that starts hardly sharp and rapidly becomes completely dull. It really doesn't care, because it's a pneumatic hammer action and the rotary action is just to clear away the dust. (It also works with masonry chisel bits if you turn the rotation off.

An "ordinary" hammer/non-hammer drill had a very inferior hammer action (when engaged). I'd have expected it to be OK with 3/16 into cinder blocks and soft bricks, but on solid concrete or hard bricks, not much or no good. I never purchased expensive bits for use with such a drill. I used cheap-as-chips Chinese carbide tipped drills sold in 6-packs and threw them away when they wore out, which they did often.

When I moved to a house built of natural stone outside and inside, the hardest bricks I have ever encountered, I gave up and bought Bosch's cheapest SDS_plus hammer drill. It was money very well spent.

nigel222
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The hammering action of the drill linked in the picture doesn't really need anything more than turning the dial to the hammer setting - it doesn't selectively "activate." It should be pretty noticeable but nothing that's going to bounce you out of your shorts.

The mechanism is usually something like two plastic poker chips rotating, which gives you some vibration, but not true hammering action like a rotary hammer.

It's likely you're just heating up the bits and ruining them quickly.

If you're setting the dial to hammer and exerting decent pressure, it's the drill that's the problem.

batsplatsterson
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Make sure you have not accidentally set the drill in reverse mode. When the bit rotates the wrong way it causes the bit to heat up and wear out. Something similar to this happened to a friend and to myself.

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Go to harbor freight and get an SDS or SDS max. Any consumer/pro drill that has a 'hammer' mode will stink compared to a proper tool. I've gone through much harder material using the SDS-Max I bought for 100$ whereas I would ruin bits with my makita or Milwaukee.

So yes, you're over heating the bit and it isn't removing the material right.

J.Hirsch
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