Section 3 - The Book of Holes
"After getting thy hole aggressively pounded, make sure you clean it really well"
Holes matter a “whole” lot! You have to know where to put them, what pattern to put them in, how to drill them and what diameter they need to be, even sometimes accurate to within 0.1mm. And did you know that if they aren’t super sterile clean, at least for glue in bolts, they will fail at a dangerously low force? See here all the things you need to get your holes drilled out.
Chapter 1 - Picking the Spot
Things to consider about where to drill your holes
Where do you want your master point to be? It will be in the center of your bolting pattern so choose carefully. And remember you don’t want more than a 45 degree angle on your anchor legs so it doesn’t put exponential force on the bolts, rather than sharing the load evenly.
Is the anchor going to serve more than 1 highline? How can the bolts be placed to best be pulled in multiple angles?
Will the hangers sit flat against the rock?
Will there be a weird hump between the bolts and the masterpoint causing unwanted friction?
How far back from the edge will the bolts be?
In hard rock it can be a foot or two away from edge but if it is too close then it can put the master point too far beyond the edge making rigging a bitch.
In soft rock it is important to stay away from the edge even 6 to 10 feet back in some cases but then the master point will need extending
What Pattern will you use?
Straight line - Careful, this is how they harvest quarry stone. This can score rock and make it susceptible to fracturing. Know your rock.
Curved pattern - Like a semi circle.
Zig zag pattern
How close, or far, should the bolts be apart from each other?
With mechanical bolts, where the cone or sleeve puts the force at the bottom of the bolt, the force is spread at a 45 degree angle through the rock. You don’t want your bolts too close to each other so the rock doesn’t see too much force (rocks can fail, not just bolts). So the rule is 10 anchor diameters apart from each other (½” x 10 = 5” apart minimum)
In softer or fractured rock, do NOT put bolts closer than 20 diameters apart or at about a foot minimum.
Glue in’s can be closer to each other as it is putting the force on the entire rock but there is no need to have each bolt closer than 5” together
How many bolts will you use?
2 Bolts - This is not very redundant so the bolts need to be bomber. If you only use two, please use minimum ⅝” diameter (standard is ½”) and a minimum of 6” deep. CMI sells hangers rated for 10,000 pound MBS that will fit on these.
3 Bolts - This is common but directional relativity means the center bolt will see at least double the stress as the 2 outside bolts. If these are good bolts in good rock this is super good enough. See the studies done on that here.
4 Bolts - This is more redundant, shares the load between the 2 center bolts and is industry standard for most highlines. See a demonstration of how forces are spread out over an anchor here.
5 or More- This depends on your area but it is very difficult to equalize this properly. It provides more redundancy but rarely would all 5+ bolts be sharing the load. This is not common.
What are the regional trends and is it correct? Don’t do anything drastically different than others have done in the area without fully understanding why they did it.
Glue in bolts are frowned upon in Yosemite even though there is nothing wrong with them. Mechanical bolts are just fine. Stick with “normal” in this case.
⅝” zinc wedge bolts with chain links are common in Moab but may not be the safest long term choice though it was the most cost effective for those installing at only $3 per total unit. So Glue In bolts are different in this case but OK to use, actually it is the more preferred way.
Chapter 2 - Drilling Basics
Here are some pointers for drilling holes regardless if you are hand drilling or power drilling.
Drill the hole the right length
Mechanical bolts should be drilled about ½” longer than the bolt to make sure it’s plenty deep and also to help for future replacement so it can be hammered into the hole all the way and be covered if removal is too difficult. Be careful though, some bolts can drop into hole while installing and you can lose your center rod like on Fixe removable triplex bolts.
Glue ins have to be the perfect length and need a notch to bury part of the eye. See the Chapter on Glue ins for more detail on that.
Measure the hole with your pipe cleaner. You can put a piece of tape on the handle so you know it is deep enough when the tape is completely below the rock surface.
IT IS VERY BAD IF THE HOLE IS TOO SHALLOW. A bolt sticking up out of the rock is not safe to use and difficult to remove. If it is even 95% deep enough it will look like it is in the rock but the hanger will be spinning and that always raises a red flag on the integrity of the bolt to someone who wants to use it.
Drill it straight.
Mechanical bolts will have a hanger and it is important that the hanger sits flat against the rock.
Glue in bolts can be placed at slight 15 degree angle back so it gets some leverage as mentioned on this FixeHardware video. However, I do NOT recommend this in soft rock for the same reason you don’t tilt a ice screw during installation. All the pressure will be on the top few millimeters of the rock if you tilt it and that can risk failure. Drill glue ins straight in for soft rock and let the entire shaft and glue do the holding rather than the angle. Bolt-Product's website (scroll halfway down) shows how stakes in the ground did better if installed in the direction of pull rather than being angled back.
Test the spot
Set the hanger (if using hangers) where you think you will drill the hole to make sure it sits flat and nice. If you really like the spot and only a few crystals are stopping you, you can chip them away, but just be sure the end product… the hanger… will sit nicely.
After drilling the hole an ⅛”, stop and check everything again. Do you like the spot? Does your hanger sit nicely? Did the rock feel/sound solid? If you goof, ⅛” isn’t a deal breaker, but if you drill all the way and then realize there was a mistake, then it is just slop.
It really sucks if you don’t have a backup drill/batteries or backup bit or backup glue tip and you can’t finish bolting. The impact bolts have on an area are debated, but everyone agrees a half drilled or half installed bolt is bullshit.
A 4-point bit drills faster and saves energy or batteries rather than 2-point bit.
Fresh bits are important because the tip/shoulders get worn down on old bits and you get an undersized hole. If the hole is too small, then you have to smash your mechanical bolt in harder which can damage it or the glue in will not have as much glue surrounding the rod.
Battery powered hammer drills and Petzl Rocpec hand drills require SDS-Plus drill bits, “special direct system”. These kind have the groves at the top so the drill can hammer and rotate the bit. Not all SDS bits are created equal. SDS-Plus is 10mm shank and SDS-Max is 18mm. So make sure you know what you are buying.
Size matters - the usable length and overall length are generally different by 2” because of the shank, or the part that goes into the drill. Remember that a 6” drill bit only has 4” that is usable.
It helps to understand all 5 parts:
- Shank: has two sets of grooves so the bit doesn’t fall out and helps during hammering.
- Head and Tip - these work together to break up the concrete. The carbide is brazed onto the head to harden the tip of the SDS bit to assist in the breaking of the concrete.
- Flute - the spiral groove which facilitates the removal of the concrete dust as the hole is being drilled.
- Land - raised portion of the spiral (similar to the crest or peak of a wave).
Chapter 3 - Hand drilling
There are some places that do not allow power tools, such as National Parks in the USA. However, if it is legal and ethical to install bolts, you can do it the ol’ fashion way… by hand!
You need a handle. The poor man’s method is to duct tape the shank with about 50 wraps but the official way is to use a Petzl Rocpec , a hand drill that accepts SDS drill bits.
You need a hammer… obviously. You can use any 12oz construction hammer but the Yosemite Hammer has an attachment cord and an eye to attach a carabiner to for clipping and the occasional yanking.
Use gloves! The thicker the better for when you occasionally miss the head of the drill.
Use eye protection! You can literally feel things hitting you in the face when hammering a rock. You don’t want rock shards in your eyes.
How long does it take?
A 4 ¾” x ½” bolt hole takes approximately 1000 hits in hard Yosemite granite. Counting is a great way to keep the stoke high. Try to hit it at least 50x before resting your arm. Find and keep a rhythm to the hitting rather than pretending you are the road-runner on crack and getting tired 20 seconds later.
It takes about 45 minutes to an hour for a 4 ¾” x ½” bolt hole in hard Yosemite granite. Softer rock can be much much quicker but you may have to drill for a longer bolt.
Keep it straight - As you get tired, you may have a tendency to not keep the drill straight. If the drill isn’t perfectly straight, it will be dragging against the sides of the hole and the friction that creates can really slow down momentum. It’s also very important to keep a drill straight so the hole stays true to size.
Don’t give it a courtesy tap, hit the drill with some umpf! You're not trying to make noise, you are trying to burrow a hole in rock!
Keep the hole clean periodically. Maybe after 100 to 200 hits. If you don’t, you are just pounding dust… literally!
Use the most important resource on the planet… friends! If the anchor is safe to “hang out” at and easy access for everyone, take turns. Hitting 100x and switching can speed things up and not feel like such a burden.
Keep it attached to you. Wouldn’t it suck if your hammer or drill rolled off the cliff or fell out of your hands?
Use fresh bits. This is especially important for hand drilling. That extra $10 won’t seem like much if you are only half done after 1000 hits because you are using a worn out bit.
Don’t slack off! Standard diameter is ½” or 12mm. Just because you have to hand drill doesn’t mean you should use skinnier bolts like ⅜” or shorter bolts than is safe.
Chapter 4 - Power drilling
Hammer drill vs rotary hammer drill - rock isn’t threatened by a normal drill spinning, you need a hammer drill. However, a normal “hammer drill” only has 2 cam/discs/gears spinning and tapping each other and is designed for “light masonry”. Unless you are drilling into some really poor quality rock, you will want a Rotary hammer drill. Those have pistons which chisel the rock while spinning. Hammer drills have a normal chuck in which a smooth shank fits in and Rotary Hammer drills require SDS bits. You can buy the best at Bosche or save $100 and buy the one from Makita that works just as well (i’m very happy with it).
Keep it straight - it’s common for people to think a drill is straight and it be completely at an angle. With all the vibration and noise, you really have to be intentional to keep that drill perpendicular to the rock. There’s no fixing a hole drilled at an angle after you see the hanger doesn’t sit flush with the rock!
Check your work after the first 2 seconds of drilling. Make sure that it is where you want it. Don’t check once and drill twice. Let's avoid swiss cheese rocks by being mindful about checking our work.
Don’t push hard. Let the drill do the work.
Don’t be afraid to pull out. To help clear the debris, just pull the bit out periodically while it’s spinning. Not the entire time like you are trying to have sex with the rock, but you don’t want to just leave it in the hole for 3 straight minutes either. :)
Know your batteries and bring enough. Don’t run out of juice and not be able to finish. Have a hand drill for a backup.
Know your target length. You don’t always want to drill the full length of the shaft so know how much of the shaft has to buried and keep and eye at that spot. Many drills have a measuring stick built into the handle called a “depth stop”. Just don’t drill too shallow, that is much worse than “too” deep.