Drilling rock with a rotary hammer for blasting?

[Sebculb]

Hola everyone,

So this is a little off topic but not too badly. I work primarily doing excavations with an old backhoe in Rocky mountainous terrain. Because of this I've been around the drilling and blasting of rock several times. One of the local dynamite dudes went out of business due to general incompetence (just flaky and would leave cracked but not sufficiently broken rocks), and the other dude is getting ready to retire soon. Sooo, I see a bidneth opportunity here. Pays pretty well as far as I can tell.

I would not be trying to work with "real" high explosives. There are cartridges available here that deflagrate rather than detonate, kinda like a gaseous slow explosion. These cartridges do not require special permits or licenses. There is also expansive cement that breaks rock up pretty well.

Anyways, the question is, would I be able to drill hard granite and the like with a medium to large electric rotary hammer drill? Not a regular size hammer drill like one of the big ones closer to jackhammer size? It has to make like 1" holes for the charges. A regular hammer drill will drill a few holes in rock for putting rebar in it to pour a foundation etc, but if I try to get into this business I'll have to make a lot of big holes in hard rock. Would a rotary hammer be an adequate tool for this? The manufacturers only talk about concrete.

The other dudes that do this use air powered rock drills and jackhammers powered by diesel compressors. This would just be a sideline for me so I'm not ready to invest like that. Tools are expensive here in Costa Rica, so a big rotary hammer would cost $700-1200 depending.

Any advice experiences insight? Thanks!

 

[4570Man]

I’ve tried an SDS max hammer drill and it’s really not up to the task. It’ll drill a few holes 12” deep but it over heats pretty quick attempting that. It doesn’t have any air to clear the hole either. And blasting also requires drilling multiple feet deep. I don’t know if they make bigger electric drills than an SDS max or not. There’s bigger electric breakers but I don’t think they rotate.

 

[Sebculb]

4750, was that sds max drill a regular hammer drill or one of the ones that has the chisel setting that doesn't rotate like a jackhammer? As I understand that's the difference between a hammer drill and a rotary hammer.

Sorry I've used regular hammer drills a few times but never owned one, and I've never touched a rotary hammer. Thanks!

 

[4570Man]

Yes they can turn off the rotation and just hammer. Here’s what they look like.

 

[Jim Nelson]

Many years ago I worked a few years in mining and found that whether underground or surface drilling water for dust control and air to blow out holes to keep them clean are just as important as rotation. Carbide bits are also a time saver but must be built so that you can resharpen them. With a jack hammer you have a string of bits that start with the largest size to start then every 3 feet or so you change both drill steel to longer and bit size to smaller until you reach your desired depth. I can't imagine an electric hammer drill or rotary hammer being very productive or economic in the long run.

 

[4570Man]

Many years ago I worked a few years in mining and found that whether underground or surface drilling water for dust control and air to blow out holes to keep them clean are just as important as rotation. Carbide bits are also a time saver but must be built so that you can resharpen them. With a jack hammer you have a string of bits that start with the largest size to start then every 3 feet or so you change both drill steel to longer and bit size to smaller until you reach your desired depth. I can't imagine an electric hammer drill or rotary hammer being very productive or economic in the long run.

I don’t think you want to wet the holes with a small hand held air drill. A tracked drill might be a different story. If the dust gets saturated it won’t blow out, packs around the bit then it gets stuck.

 

[MossRoad]

I've never drilled granite. I've drilled plenty of concrete. Really hard concrete is what, 6000psi? Granite is listed as 19,000psi. I'd say rent a rotary hammer if you can and test it out on some granite. That's about the only way you'll know yourself how it works in your conditions.

Found this interesting video on hammer drill VS rotary hammer with 1/2" bit in concrete. Really illustrates the difference. But again, this is concrete not granite, and 1/2" VS 1".

 

[chim]

Good video. The hammerdrill sounds like an angry bee and works OK in block walls. If you have concrete the rotary hammer is the ticket. The rotary hammer has a heavy metal slug inside that is propelled by trapped air between it and a piston. The slug smacks the snot out of the rear end of the drill bit. As the guy noted, the weight of the rotary hammer provides enough force. No need to push hard. It does help to pull the bit out to clear the dust on deeper holes.

Years ago we tried using a core machine with water and a 5" diamond bit to go through a granite slab and gave up. Same setup went through either concrete the blue/gray limestone like butter.

When I worked in the quarry, they'd bring in a well drilling rig for blasting. On construction sites they'd use wagon drills. Any hand drilling was with something like a 90 pound jackhammer powered by big tow-behind compressors.

 

[oosik]

Around these parts we are "blessed" with basaltic lava bedrock. About the only natural material that's harder - diamonds. I have 80 acres and 675 T-133 steel fence posts. About 125 of these posts sit right on top of this bedrock. Held there, in place, by various forms of triangular support systems. Jerry-rigged comes to mind.

Slowly but surely - 2" diameter holes are being augured into this bedrock - T-post flukes are knocked off - insert the post, followed by a dry sand/cement mix.

I have about 40 more to go and then it's done. I've tried a hand held rotary hammer. This IS NOT the answer. It's VERY slow - bits break regularly - they simply are not up to this job.

My neighbor IS the answer. He has a large wheeled commercial air compressor and a REAL jack hammer. As he has the time - brings this rig over and we knock out a few more holes.

One more time and we can knock out these last post holes. I go over to his place and clean out his feeding pens. All of his tractors are too big and not set up for this type job.

 

[4570Man]

Around these parts we are "blessed" with basaltic lava bedrock. About the only natural material that's harder - diamonds. I have 80 acres and 675 T-133 steel fence posts. About 125 of these posts sit right on top of this bedrock. Held there, in place, by various forms of triangular support systems. Jerry-rigged comes to mind.

Slowly but surely - 2" diameter holes are being augured into this bedrock - T-post flukes are knocked off - insert the post, followed by a dry sand/cement mix.

I have about 40 more to go and then it's done. I've tried a hand held rotary hammer. This IS NOT the answer. It's VERY slow - bits break regularly - they simply are not up to this job.

My neighbor IS the answer. He has a large wheeled commercial air compressor and a REAL jack hammer. As he has the time - brings this rig over and we knock out a few more holes.

One more time and we can knock out these last post holes. I go over to his place and clean out his feeding pens. All of his tractors are too big and not set up for this type job.

I had to have a blaster come drill and blast for a septic tank hole. He had to drill holes either 1” or 1.25” about 2’ deep. He had an air drill and a diesel powered compressor and it’s a completely different animal from an electric rotary hammer. Honestly I’m surprised there’s no in between the hand air drills and a mining tracked drill. It seems to me like a walk behind skid steer with some kind of vertical lift attachment like a forklift mast would be a dandy tool for jobs not fit for a big drill and a real man saver from the jackhammer. Hydraulics could handle the brunt of the work and a smaller air compressor could blow out the hole.

 

[oosik]

Ha, ha, ha, ha - 4570Man - you are SPOT ON. The neighbors "rig" is what you see being used on highway dept projects or the like. Diesel powered air compressor and a real, honest-to-God jack hammer. He tows it over behind his pickup. Hook it up to my tractor and off we go.

He even let me try the jack hammer - once. That is a unit that separates the real men from the weenies. I'm somewhat of the latter. I drilled two holes - my shoulders & arms felt it for the following three days.

However - his "rig" is the perfect setup for drilling holes for the T-133 posts.

 

[Sebculb]

Thanks everyone for the advice, I'm gonna have to think this one through a bit more it sounds like.

 

[BrokenTrack]

The sad thing about modern times is that people often think, the only way to do something is how the professionals do it. That is not always true because a person can go old-school.

I do a lot of digging, and thus hit a lot of rocks. As costly as blasting companies are, I found fire and water breaks rocks up pretty darn good.

Wood is cheap, but puts up a lot of smoke and spark, which is fine when snow is on the round, but in dry times, coal works better. It burns hotter, has a nice bed of coals, and gives off a nice heat haze instead of smoke if you use anthracite coal.

Just get a nice hot fire going, then douse the rock or ledge with lots of water. It will break by its own. If it does not break up enough, just redo the fire and water trick.

A person can buy a lot of coal for what a blasting company would charge to come in and bust up a rock or ledge...

 

[PILOON]

There are a few gas powered rock drills out there.
Punjar was one brand, but others exist. (Kango also has some versions)
Used both at one time or other and they are effective, just a bit slower than big rigs but very effective. Just heavy and bulky compared to big rigs powered drills.

I'm not a pro blaster but live in rock haven and needed blasting done from time to time to do renovations.
Shucks we even blasted under houses and once resorted to 'plug and feather' rock splitting into manageable chunks.

 

[Egon]

Ha, ha, ha, ha - 4570Man - you are SPOT ON. The neighbors "rig" is what you see being used on highway dept projects or the like. Diesel powered air compressor and a real, honest-to-God jack hammer. He tows it over behind his pickup. Hook it up to my tractor and off we go.

He even let me try the jack hammer - once. That is a unit that separates the real men from the weenies. I'm somewhat of the latter. I drilled two holes - my shoulders & arms felt it for the following three days.

However - his "rig" is the perfect setup for drilling holes for the T-133 posts.

There are different methods to using a jackhammer. Some make it hard work, others are quite easy on the body. In the easy mode only a light guiding touch is require most of the time.

 

[Mat4644]

Drilled several granite rocks for fountains with SDS Max rotary hammer. Definitely doable. Many videos of products such as Ecobust using rotary hammers in granite. One thing I noticed is granite boulders varies greatly. Some drill much easier than others. No idea speed drilling vs a pneumatic rock drill. If possible borrow or rent one and do a test to see if the speed is something you can make money with.

We have split field rocks around my Grandfather drilled with hammer and rod drill. Dynamite used to split and pieces hauled out with horses.

 

[Sebculb]

Matt4644 I'm choosing to listen to you for now, my neighbor's kid works as a rep for hilti here and first thing he said was buy 4 point bits, sounds like he at least knows the first thing to say. Hopefully he will be able to get me a good price.

I still have to talk with the engineer at the blasting supplies company. Until now I've only talked with a salesperson who confirmed the existence of these products and that no license is needed for their purchase. But I have to talk to their tech support first to know if this is feasible. If they say I'm just wasting my time I'll be inclined to believe them. Like for example, every hole has to be two feet deep. That'd kill the idea.

Thanks again everyone. I'll post up what the engineer says and what I decide to do.

 

[grsthegreat]

when we blasted rock up by mammoth lakes, calif the holes were 4' deep, packed with explosives. they used a real jackhammer/drill and diesel compressor. very hard work. that **** jackhammer weights a heck of alot without the long bits. i wouldnt want to mess with the dudes drilling the holes.

 

[radios1]

this is what you need.

 

[4570Man]

this is what you need. View attachment 668734

That’s a breaker. Completely different tools and a machine that size is almost useless against bedrock.