Was drilling some concrete today, about 2″ down was something hard. Carbide drill would not drill through and finally melted carbide on the end of the bit. what is so hard that carbide will not drill it? Maybe the ol boy put all of his X wife’s diamonds in the slab.
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George
Remember the early bird gets the worm, BUT it’s the second mouse that gets the cheese.
Replies
Might be rebar? Tough, not hard.
Bill
Could be just a bad drill. I've had a tip disappear in the second hole, changed drills and continued for another 25-30 holes in the same slab.
Yeah, rebar or a very hard granite pebble. If a pebble, insert a qood quality drift pin, hit it hard with a 2# sledge, to shatter the pebble. Blow the pieces out. Resume drilling.
Yeah, usually when that happens its the re-bar. You can tell when you pull the bit out and it has tiny metal shavings on the tip. Next time when you are drilling and it won"t go no further, stop immediately and try a different spot. You might save the bit.
Both concrete and rebar can have what is sometimes called 'inclusions'.
In concrete I understand that a considerable amount of furnace and incinerator 'clinker' is used as filler in it. This stuff can very hard, glasslike and tough. Once the clinker takes the edge off the drill bit if the bit gets through the inclusion the concrete is abrasive enough to cause the bit to heat to the point it melts and reforges itself into a blunt plug.
Rebar is mostly made of recycled steel. There can be glassy hard spots because of this. This, and other variations in the hardness of the bars, can also make these units bend funny.
These deposits can defy carbide and even oxy-acetylene cutting. Spend a long time in one spot fighting an inclusion. Move over a half an inch and it melts or drills like butter.
When I was siding our concrete house I went to the home center and bought all the 3/16" bits they had, several times. Finally wised up and bought a Hilti SDS drill. End of the bit problem.
You didn't say what bits you were using, but there's a world of difference in SDS from straight shank. On the business end, not just the shank. I'm sure it was just the stone in the concrete that was doing mine in.
PAHS Designer/Builder- Bury it!
I've had really good luck using Bosch bits instead of the Tapcon bits.
If you did indeed hit a rebar, that would explain why it stopped drilling and melted. Percussion-rated carbide bits don't drill worth a snot in soft material like steel. They go through stuff by shattering it and then pushing the busted pieces out of the way with a minimal rotation. Rebar won't shatter no matter how hard you hit it, so the bit just pounded and smeared itself to death trying.
The best way to drill a lot of holes in a slab is with something like a Bosch Bulldog, which runs SDS Plus bits. The difference between that and an ordinary drill in 'hammer drill' mode is amazing, even in the small sizes you need for Tapcons. Had a 2x6 red pine floor to lay on top of a slab last year, so I bought a Bulldog to drill the holes for the Tapcons to screw down the sleepers. Over 600 holes; only used 3 bits--I snapped the first two by being careless, and the third one is still in good shape. (Pretty sure I didn't hit any rebar, though--cheap-a$$ contractor who built that place probably never heard of the stuff....)
Dinosaur
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