Drilling Hard Rock With Carbide

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SteveHGraham
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Drilling Hard Rock With Carbide

Post by SteveHGraham » Tue Jul 16, 2019 8:09 pm

Today I pulled a 6-foot boulder out of my yard. I thought it was two smaller rocks, but when I looped a strap around one end and pulled, one large rock came up.

I was surprised to see that I could move it with a strap when I could not get anywhere with the tractor's hydraulics and a subsoiler.

I still have a couple of big rocks I hate. I am wondering if I should drill deep holes in them, epoxy heavy eye bolts in place, and use the strap again.

Here is the question: is there any hope I can drill through chert with a rotary hammer and carbide bit? I don't want to drag the tool out in the sun and suffer if it's hopeless. Chert is a hard rock made from little bits of quartz.
07 16 19 Giant rock pulled out with Kubota small.jpg
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warmstrong1955
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Re: Drilling Hard Rock With Carbide

Post by warmstrong1955 » Tue Jul 16, 2019 9:00 pm

I've drilled miles of quartzite....quite similar, but generally harder (a lot) and more abrasive. Talkin' about rock that is 50,000 PSI and harder.
Regardless, plain rotary won't cut it if it's hard. Percussive/rotary is what you need, like your hammer drill. As far as hammer drills....yes....we used Hilti's to put in spads in quartzite. (Our real drilling was done with jacklegs & jumbos) Just 1/2" and 5/8" diameter holes a couple inches deep. Spads are just hooky-doos to hang survey strings, for marking center lines, grade lines....as well as & lasers & things.

So anyway....much depends on your hammer drill.
For one.....carbide is a requirement....not an option. Quartz is abrasive. I can tell you stories.......
The other, is that chert, or quartzite, requires a lot of blow energy to break it....so it depends on your hammer drill. More hammer than rotation does better. It's brittle....but has a very high compressive strength.

Trying to be brief.....hope that helps.

Bill
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Russ Hanscom
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Re: Drilling Hard Rock With Carbide

Post by Russ Hanscom » Tue Jul 16, 2019 10:02 pm

Drill a row of holes 2" apart(say 5/8 dia) where you want it to break, then make up tapered pins out of whatever steel rod you have(say 3/4 dia) and drive them into the holes. The rock will break along the line. Rock is very strong in compression, but weak in tension.

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SteveHGraham
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Re: Drilling Hard Rock With Carbide

Post by SteveHGraham » Wed Jul 17, 2019 10:20 am

The problem with splitting these rocks is that it doesn't get them out of the ground. If you break a big rock like this, you end up with two rocks, still large, wedged against each other, holding each other in place. The advantage of pulling them is that you can move a very large rock very quickly. If I can pull them out whole, it will be much less work, and I will end up with landscaping rocks I can use or sell.

My drill is a big Makita SDS-Plus. It goes through concrete like cheese. I haven't tried chert yet.
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warmstrong1955
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Re: Drilling Hard Rock With Carbide

Post by warmstrong1955 » Wed Jul 17, 2019 10:52 am

Makita SDS is a good hammer drill.
Don't expect your chert to drill as easily as concrete. Concrete is about 4000 psi, chert, depending on the flavor, is roughly in the neighborhood of 35,000 to 65,000, if I recall correctly. It won't take long to figure out if the SDS has enough blow energy to drill it.

Good luck.

Bill
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SteveHGraham
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Re: Drilling Hard Rock With Carbide

Post by SteveHGraham » Fri Jul 19, 2019 5:43 pm

I kept digging around the rock, and when I uncovered a mass about as big as a card table, I decided to try pulling it out with a strap. That didn't get me anywhere. The Makita was nearby, so I decided to play with it, using a 1/2" bit.

The stone isn't all that hard to drill. The rock is very strange. Some parts are like flint, and others are like sandstone. You go slow through the flinty bits, and then when you hit the soft stuff, things speed up quite a bit. The bit I'm using is 18" long, and it doesn't take long to bury it.

I have a chisel bit, so I tried that to see what it would do. Very surprising. Because the hard parts of the rock are so brittle, you can carve through it pretty quickly with the chisel. I'm thinking I may just carve off the parts of the rock that stick up into lawnmower territory and rebury it.

I may have a pretty good shot at breaking off the parts that are holding it in the ground. I would not be very excited about splitting a big round rock, because I would end up with big pieces that still had to be dug out, but this one has relatively thin projections on it. If I could bust a couple off, I might be able to use the strap on the skinny projection that points up from the main mass.
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warmstrong1955
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Re: Drilling Hard Rock With Carbide

Post by warmstrong1955 » Sat Jul 20, 2019 11:56 am

Sounds like you have a conglomerate....like leaverite! ;)

Another option: https://www.amazon.com/Packs-Heavy-Feat ... pons&psc=1

I've never used any this small, but with harder brittle rock, they do work very well.
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SteveHGraham
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Re: Drilling Hard Rock With Carbide

Post by SteveHGraham » Sat Jul 20, 2019 3:38 pm

I have already ordered some wedges. We'll see if I get anywhere.
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warmstrong1955
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Re: Drilling Hard Rock With Carbide

Post by warmstrong1955 » Sat Jul 20, 2019 5:48 pm

It's just a matter of what spacing you can get away with, and sometimes, how many extra holes you need to line drill between the holes you wedge.
All dependent on the rock....
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SteveHGraham
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Re: Drilling Hard Rock With Carbide

Post by SteveHGraham » Sat Jul 20, 2019 6:03 pm

I found out my little Kubota can put enough stretch in a 4" tow strap to make the end sail by my head when it comes loose. I think reducing the size of the objects I pull will add to my lifespan.
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liveaboard
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Re: Drilling Hard Rock With Carbide

Post by liveaboard » Mon Jul 22, 2019 1:49 am

or use chain; that's what I do for heavy pulling.
If it breaks loose it doesn't snap back much and it stays near the ground.

RMinMN
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Re: Drilling Hard Rock With Carbide

Post by RMinMN » Mon Jul 22, 2019 6:36 am

SteveHGraham wrote:
Sat Jul 20, 2019 6:03 pm
I found out my little Kubota can put enough stretch in a 4" tow strap to make the end sail by my head when it comes loose. I think reducing the size of the objects I pull will add to my lifespan.
Your little Kubota can put enough stretch in a 4" tow strap to make the end remove your head if it hits it. Put something in the middle of the strap to restrict it like an old tire or change to something that does not store energy like the strap does. Chains do not stretch much so usually just fall to the ground if they slip or break.

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