Concrete – Masonry bits dulling after 3-4 holes

bitsconcretedrillmasonry

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

Best Answer

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.

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