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George Seal
11-05-2004, 08:55 PM
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.

George Hodge
11-05-2004, 09:26 PM
I've hit re-bar and done the same thing.

J. R. Williams
11-05-2004, 09:30 PM
George
You may have hit a round hard Aggate stone in the concrete. Very common in our area and it takes a hard hitting impact hammer to break thru. Carbide merely skids and gets hot.

JRW

Ries
11-05-2004, 09:33 PM
I cant count how many carbide drill bits I have toasted with the rotohammer- but its a lot. And these were high quality bits- unlike those freebie bits that come with the tapcons, which are usually not very long lasting. Concrete is full of hard stuff, mixed randomly with soft stuff- rocks and rebar. The combination makes for stresses on bits- even though the carbide itself is hard, it can get hot and melt its braze joint, or just break, when it is trying to drill partially thru something hard, while part of the bit is still in the soft concrete. I have had the rare occasion when the carbide bit hits the rebar exactly dead on, and drills thru it, but the geometry of the bit is not designed for rebar- its meant for concrete, so bits are a casualty from time to time. Sometimes you can go in with a fresh, sharp bit, and go thru- but sometimes you just need to drill another hole in a different place.
Drilling holes and placing anchors in concrete is never a sure thing- I always try to design in redundancy, with extra fasteners, because there will always be one that just spins, or doesnt seat all the way, or screws up in some other way. I usually take a cutoff disc on a 4 1/2" grinder with me when I am setting concrete anchors on jobsites, along with a crowbar, extra bolts, and some epoxy, in case I need to glue on a bolt head or nut to make it look right after I break one and cant get it out.

Paul Alciatore
11-05-2004, 09:41 PM
I'm glad I am not the only one. Ditto on the hard round stone. Been there, done that, ruined my tee shirt.


Paul A.

vinito
11-05-2004, 10:15 PM
Sounds like we've all been there & done that. Through a trial and error I found this works for me:

First, be sure the bit isn't already dull to begin with. You don't necessarily need a green or diamond wheel to put some kind of sharp edge back on a masonry bit. Use an angle grinder or abrasive cutoff saw to preserve your nicely dressed bench grinder wheels.

Keep a cup of water next to you when you're drilling. Every few seconds, dip the bit in the water like you're quenching it and cool it off. This does two things. 1) keeps the carbide from un-brazing itself from the bit. 2) causes small chips in the carbide that kind of re-sharpens it - kind of like flaking flint arrowheads.

When (not "if") you find a hard pebble while drilling, oscillate the drill up and tap it down like a hammer drill would. It doesn't have to be fast, you're just trying to chip the pebble so the bit can get a bite on a corner and work your way through. Don't forget to dip in the water.

Drilling holes in concrete is a quick and dirty thing. You just need to make a hole so you can screw in a tap con. The bits never last long, so just blow your way through there. You should count on having two or three extra for the small ones for insurance.

$.02

p.s. Don't forget to shift to correct drilling practices when you get back to working metal. http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by vinito (edited 11-05-2004).]

J Tiers
11-05-2004, 11:24 PM
My house was built in 1935. I dunno what they used for concrete, but it is really hard. Harder than that. A rotary masonry bit is dull just holding it nearby.

I needed to drill a bunch of holes in it. Nothing worked.

But, after me cussing up a storm, and busting one drill motor on the job, the wife's voice finally cut thru the noise reminding me there is a U-Haul nearby, that rents tools.

Off I went, Bosch hammer drill came back with me.

About 15 minutes later, I had drilled holes in everything I needed to, plus a few I figured I'd want later.

It didn't care about agate, any form of quartz, rebar, or whatever. It all came out of the hole as powder. Just chewed it up and spat it out.

Those things absolutely rule.



[This message has been edited by J Tiers (edited 11-05-2004).]

Rustybolt
11-06-2004, 12:20 AM
J. The older concrete gets the harder it gets. The stuff just keeps curing.

J Tiers
11-06-2004, 12:44 AM
<font face="Verdana, Arial" size="2">Originally posted by Rustybolt:
J. The older concrete gets the harder it gets. The stuff just keeps curing.</font>

Yes, and they used a rich mix, too, none of this new-fangled porous stuff.