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.