Drilling the rock, part 2

Bret4207

Well-known Member
Okay, so I'm figuring on drilling my ledge rock and using anchor bolts to secure braced pipe bases for my Tee posts. Got the power end of things sorted out, but the hammer drill end is up in the air. I've used 1/2 and 9/16" Makita hammer drills for concrete. No real complaints, but I either lent out or someone stole my 9/16 drill so I have to replace it. I see the SDS type drills for sale. Obviously much heavier built that the pistol grip type I had. I might be drilling 100-150 holes or more. Is it worth the extra money to go with an SDS type? I'm figuring the holes themselves will be 1/2" or maybe 5/8", 2" or so deep. Thoughts?
 
You want a rotary hammer, not a hammer drill. So yes, SDS, SDS Max or spline (pretty much obsolete) drive. SDS only has bits up to 1", the others go larger. I would recommend you go with SDS max to drill in rock,
the smaller drills will be slow. I've done similar to what you are looking at with an older Milwaukee spline drive, it worked fine.

I've also drilled holes with an air rock drill. For your project, I would look to rent a drill and compressor if possible. Will be easier and faster if you can drill holes to drop t posts or pipe into. There have to
be places in your neck of the woods that have drills for rent, its not like there is a shortage of rock there.

I used to live in N Maine, I eventually bought a wrecked utility pole truck to build fence. Truck wasn't road worthy, but had a hydraulic auger that would cut through concrete. Even then, I had one hump of rock that
was too hard to drill for a corner post. Found a 4' boulder and parked it there. Anchored my fence wire to the boulder.
 
Bret: just a word of caution--there's a big difference between drilling concrete and drilling solid rock, especially hard rock, which from what you'd mentioned earlier sounds like what you're dealing with. You'll let the smoke out of most hammer drills in short order using them in rock, and the same with typical masonry bits. You're going to need a rock drill and the appropriate bits for your rock type, which will mean a bit of research, but it's worth it if you've got 100+ holes to drill--you'll be time and money ahead doing it right from the get-go.
 
Agree with others. Go to your local rental center. Tell them what you
are doing and they will fix you up. You will most likely need a garden
hose if they trick you out with a core bit rig. That will make bigger
holes but is faster and very neat. Then you can use industrial glue in
the hole and NOTHING will ever come loose. For goodness sake use ear
and eye protection. Face mask if needed. Concrete dust is a killer.
 
I still think a coring bit would be the best way to go. Big time saver, plus you'll end up with clean holes.

I've got a 9/16" Makita, but I'd never subject it to trying to drill rock, even with a coring bit.
 
You need at least a demo hammer/chipping gun size rotary hammer drill. A rental house might be your best bet. I'm wondering what kind of rock you are drilling into. Expansion bolts will work fine if it resembles concrete which is a consistent compressive strength. If its softer rock, or the decaying upper layers like some rock will have, these fasteners may or may not achieve the pull or shear value you want, especially at that depth. Think of the moment force applied to the post. You'll know once you test this out,and as much as the engineering jargon may not be appreciated, mock one of these up and see what it does before you go for all of them. Use care with edge distances and fastener spacing. The substrate (rock) may be unpredictable, too close of spacing and it fractures. I have fastened into rock before, nothing real hard, but it was not like concrete either. You may need to go deeper with the fasteners to get the strength. Freeze though cycle also comes to mind, epoxy anchors might be of interest here.

I have a an old Hilti TE-52 rotary hammer drill that would handle this kind of work, unless its super hard rock like granite or something.

This size drill or larger is likely your best bet. Rental house should have what you need. Links below show ones like mine, you just need something that size, Bosch, Hitachi, Hilti etc. The one on ebay if in decent condition could be a decent buy at that price. Mine is the same age and was used on commercial construction projects yet works like new today. I have taken good care of it, which helps.
TE 52

TE 52 on ebay
 
I have a HF sds hammer drill, works great, have drille 100's of holes with it. Drills most rock easily. In N MN we have some
rock that has Taconite, or a form of iron ore in it, that's tough to drill.
 


Okay, thanks everyone. I gotta get another hammer drill anyway for concrete. I might just go bigger no matter what. I'll talk to some local drillers on the rock issue.
 

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