How do you drill REALLY hard rock. Diamonnd drills?

Bill, I have used air powered drills. The one I used was for putting in 4" wide by 8 foot deep holes in sandstone. Turned counter clockwise. Had a diesel powered compressor attached to fire hoses 100' below.

It was basically a jackhammer with rotation. In order to keep it stable, I had to throw my rope over the top and basically ride it. It was 80 lbs, not counting the weight of the drill steel.

I did drill some 1.5" horizontal holes with it. It took a few of us just to get it started.

Is this the sort of thing you are talking about? I have never seen a scaled down version for small holes. I don't know how you'd make it practical either. Please elaborate.

The quartzite that I have drilled in takes a long time and patience is required. I typically use 3 drill bits and rotate them, so that they never get too hot, I have also tried dipping the bits in a plastic water bottle, not sure how much that really helped, but did anyway. I also like the bosch bulldog extreme drill bits, seemed to last much longer than the hilti bits I had been using.

highaltitudeflatulentexpulsion wrote: I've never drilled anything close to this hard but find the topic very interesting.

I have drilled some rather soft limestone and I go really fast. Could it be that you are accustomed to moving too fast?

Another thought. It's a 15' band at the top of the cliff. How tall is the cliff? Seems almost like a section for a nice run out. If it's typical overhanging seaside limestone, that's perfectly safe. If it's tall enough that is.

The limestone here varies from medium-soft (Tufas/flowstone) to bullet.   I'm used to letting the drill decide how fast to go with average pressure.  

highaltitudeflatulentexpulsion wrote: Bill, I have used air powered drills. The one I used was for putting in 4" wide by 8 foot deep holes in sandstone. Turned counter clockwise. Had a diesel powered compressor attached to fire hoses 100' below.

It was basically a jackhammer with rotation. In order to keep it stable, I had to throw my rope over the top and basically ride it. It was 80 lbs, not counting the weight of the drill steel.

I did drill some 1.5" horizontal holes with it. It took a few of us just to get it started.

Is this the sort of thing you are talking about? I have never seen a scaled down version for small holes. I don't know how you'd make it practical either. Please elaborate.

We called her "sweaty betty" since she was spraying oil everywhere.

So it looks like it must have been 61lbs, not including the drill steel and oil weight. It still felt like a lot. It's a cool gadget for industrial use. I used it to install the upper anchors for a rockfall fence.

I can't imagine a rock climbing scenario where it'd have a use.

John,

The cruciform bits are generally intended for drilling reinforced concrete where there exists a risk of contacting reinforcement bar and in theory the in-hole temperatures are lower than drilling rock. If standard bits are used and the operator contacts rebar then the bit will jam causing the drill to jerk and potentially cause a broken wrist / injury. This is why the cruciform bits turn purple very quickly in hard rock drilling - although they drill faster due to the 4 cutting points.

The diamond core bits from Ukam will cut through anything and I use them for extracting old bolts buuut it can be a slow process. Water and the correct feed pressure and rotation are required to optimise the cutting but it can be winged somewhat with a small water plant mister and being careful. You will need an SDS+ chuck adaptor into which the core bit is inserted (just like a regular wood drill bit) and the drill itself is set to rotation only (no hammer action). The issue with these pricey bits is that any measurable sideways leverage can cause the sintered head (containing the industrial diamonds) to snap off. Core drilling IMHO has largely been superseded with the excellent N.American techniques for bolt removal eg Greggerman.

Cheers,

Francis

Drilling smaller holes as a pilot before switching out for 14mm would definitely help.

I do this all the time when placing 16mm BP bolts, drilling 12mm or 10mm first

Worth pointing out that if drilling solely with a diamond core bit then any adhesive used for fixing a glue-in bolt into the hole should be certified for use in diamond cored holes...Or rough the hole up!

There´s a band of rock at the top of the limestone cliffs in Dorset (UK) with the same problem, it´s called hard cap and the only way the quarrymen can get to the building stone below is by blasting (hard cap is considered unworkable by the stone companies).The climbers have more or less given up trying to drill it but if the really have to bolt then they just go slowly and cool the bit by squirting water down the hole. Half an hour for a 12mm hole seems normal!
Like Francis says use a 2- point drill not a 4 and keep pulling it in and out to clear and cool. The diamond core drills only go 70mm deep and that is a real struggle as well. Even using a resin rated for diamond cored holes you should roughen them, in hard stone they still don´t really get the bonding you would in concrete as it´s not porous enough.
Personally I just wouldn´t bolt that piece of rock!

I've never heard of a 3/8 core drill bit. The whole point of a core drill is to drill a core that can be removed for sampling or running pipes and wires. You would need a generator and something to mount the thing too. They are heavy and have to go in dead nuts strait. 

If you know of a sturdy light battery powered coredrill by all means please let me know, it would make my job much easier. 

John Byrnes wrote:There's a 10' horizontal roof over this wall, so it's hard to get a rope over the prospective route.    (For the first route, I dangled in the wind for an hour swinging a hook at the end of a triple sling until I could hook a pocket and pull myself in.)

Read Jonathon Wright's comment again! I think he is 100% correct. Iv'e also broken numerous of those 4 point Hilti tips. Then if you are drilling into that same hole, the steel is still in there creating the illusion that the rock is harder than it really is. Judging by the look of your bits, you were trying to drill without a tip for a long time. This does not work. New bits and new holes should fix the problem...

Jim Titt wrote: There´s a band of rock at the top of the limestone cliffs in Dorset (UK) with the same problem, it´s called hard cap and the only way the quarrymen can get to the building stone below is by blasting (hard cap is considered unworkable by the stone companies).The climbers have more or less given up trying to drill it but if the really have to bolt then they just go slowly and cool the bit by squirting water down the hole. Half an hour for a 12mm hole seems normal!

Like Francis says use a 2- point drill not a 4 and keep pulling it in and out to clear and cool. The diamond core drills only go 70mm deep and that is a real struggle as well. Even using a resin rated for diamond cored holes you should roughen them, in hard stone they still don´t really get the bonding you would in concrete as it´s not porous enough.

Personally I just wouldn´t bolt that piece of rock!

But I've rapped over the line and it's amazing and unique!  Most of the route will be on glassy purple rock that has pockets but very low friction; different than any other route on the island.    And the yellow rock forms these crazy finger-buckets that look like whipped meringue on the headwall...  "It's gotta be done!"  (to quote Layton Kor)

As I said earlier, the yellow hard stuff is rare, and as far as I can tell, is only at the top of the route.  It's not clear how much of it is there, ie. how thick or wide the layer is, since It's about 1" under the surface.  So I'm hoping most of the route is normal drilling and that I only have to do Extreme Bolting for the last bolt and anchors.  

Darren Mabe wrote: I've used a stick clip for this situation.

Great idea.  

Thanks to everyone who's posted so far, especially Francis.  My tactics are solidifying:

Talk to Hilti about drill bits, whether RE-500 will hold in hard cap, and whether they'll comp me a bit or two.
Drill a 3/8" hole first, then 7/16", then 9/16" (9.5mm, 11mm, 14mm).
Remove the bit frequently and shoot water into the hole and onto the bit before it gets really hot.
Be patient and have several bits of each size on hand.

Drew Spaulding wrote: Read Jonathon Wright's comment again! I think he is 100% correct. Iv'e also broken numerous of those 4 point Hilti tips. Then if you are drilling into that same hole, the steel is still in there creating the illusion that the rock is harder than it really is. Judging by the look of your bits, you were trying to drill without a tip for a long time. This does not work. New bits and new holes should fix the problem...

Yup, you and Jonathon are right.  I'm sure the tips are still in there.   In my defense, I had never encountered such hard rock before, I was holding the drill over my head with one hand, hanging from some rather dubious hooks, with nothing that would hold fall between me and a large pendulum into a dihedral.   So yeah, I just held the trigger down and hoped!   

Jake G. wrote: I've never heard of a 3/8 core drill bit. The whole point of a core drill is to drill a core that can be removed for sampling or running pipes and wires. You would need a generator and something to mount the thing too. They are heavy and have to go in dead nuts strait. 

The smallest one my suppliers sells is 1/8" OD but possibly someone else makes them smaller.

Jake G. wrote: I've never heard of a 3/8 core drill bit. The whole point of a core drill is to drill a core that can be removed for sampling or running pipes and wires. 

We use tiny diamond core bits all the time for applications other than sampling or conduits.

Just got off the phone with a Hilti engineer.  

Drilling very hard rock: The short, expensive answer is a diamond core drill with a water delivery system (see post above).  For me, this seems kinda like overkill for 3 or 4 holes.  

So if I don't do that, he recommended NOT drilling progressively larger holes (3/8 then 7/16 then 9/16) but to just go with the biggest size right away.  The larger mass of the drill tolerates heat better.

Don't let the drill heat up and then quench (and possibly crack) the drill.  Try to keep he drill "finger hot" (touchable).  Be patient.  Drill a little, pull it out and put water on it and in the hole, go again.  I'm thinking a 2sec drill, pull out, add water to the hole and drill, drill 2sec, etc.   I'll have to experiment and see how hot the bit gets.

He says the 4-bladed "CX" bits would be best for this, not the two-bladed ones.  

We were speculating about what kind of rock was under there.   He suggested that, once I hit the hard stuff, just trying a normal metal drill without hammering to see what would happen.   Might be worth a try.

Just FYI.