masonary bit question

April 19, 2016
Today I installed five clocks, four were on cinder block wall. Using small platic anchors, and a 1/36 masonary bit in a high speed hammer drill.
What I noticed, after about 1/8 or so into the wall, the bit progress was a bit faster. Took a lot of work to get the first 1/4 inch or so.
Are the surfaces of cement harder? Or does the tip of the bit heat up and work better when it's hot?
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Christopher A. Young
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| Are the surfaces of cement harder? Or does the tip | of the bit heat up and work better when it's hot? |
No. Better to cool it with some water. You may have hit a pebble. Concrete can vary a great deal in terms of hardness. Some is soft. Some is nearly impossible to get through.
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wrote:

Depends how much Viagra was added to the cement. More viagra makes it get HARDER! :)
Seriously, the very surface often has more portland cement because of troweling. So, it may be a little harder. Also, the rock may be quite a bit softer, but that depends on where the quarry is located. Your bit is going thru stones, sand, and the actual cement. So there will be a lot of variances as you drill thru it. Also, some concrete blends are harder than others. It depends on how much portland cement is added, and in the case of precast concrete, it's harder yet, based on other additives. Dont forget, you could drill thru rebar and wire mesh too.
You DO NOT want your bits getting hot. Run a slow trickle of water as you drill.
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On 4/19/2016 10:39 PM, snipped-for-privacy@unlisted.moo wrote:

Well, that makes sense. Might been different hardness, near the surface.
In this case (four holes, about 1/2 inch deep, timed about ten minutes apart), not much chance of over heating a drill bit.
I'm guessing if I set up a garden hose or some cooling system, the church would not be pleased with all the water and cement dust running down the class room walls.
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On 4/19/2016 9:12 PM, Mayayana wrote:

Interesting. I remember all four were about the same. Slow going at first, and then the speed improved.
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On Tuesday, April 19, 2016 at 7:38:55 PM UTC-5, Stormin Mormon wrote:

...even if you meant to say 1/32"? They don't plastic anchors that small...3/32" possibly. I've bent 1/8" in masonry...can't imagine putting the necessary pressure with a hammer drill on "1/36 in"! Never noticed any difference in hardness.
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On Tue, 19 Apr 2016 18:12:57 -0700 (PDT), bob_villain
I bet your wife does ........... :)
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I have no idea about the relative hardness of specific areas of concrete, but what size bit were you really using?
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On 4/19/2016 9:21 PM, Gordon Shumway wrote:

Total brain failure. Sorry. 3/32, which was smaller than 1/4. It's the bit that is sold for 1/4 tapcons. My apologies to the gentle readers of this list.
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Stormin Mormon wrote:

Remember that he tip of the bit - the cutting part - is "V" shaped. When you first start drilling, only the very tip is in contact with the concrete and the going is slow. As you go deeper, more and more cutting surface is in contact and the cutting is faster.
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On 4/20/2016 7:10 AM, dadiOH wrote:

Maks more sense than most ideas. Might be the correct one.
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[...]

Yes. Concrete continues to harden for decades, by absorbing carbon dioxide from the air. This obviously happens from the outside in, and, yes, the outside *is* harder than the inside.
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