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two-shoes
Trad climber
Auberry, CA
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Mar 30, 2015 - 08:04am PT
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I feel like I need to defend the use of Self-drives in their subterranean applications.
I used these self-drives, with 3/8" SS cap screws of grade five hardness, in limestone caves back in the 70's and early 80's. Cap screws tighten with allen wrenches.We would coat the inserts with a little bit of axle grease after they had been drilled and set. They actually work pretty decent, I think, for medium hard rock such as limestone. If the rock had been metamorphosed into a hard marble, it can be almost as hard as most granitic rock, and no better than drilling in granite. But, with the limestone, usually just one self-driving insert is needed, and because the teeth aren't dulling so badly the hole tend to stay tighter and rounder. The big advantage to the self-drive system is its cost. I remember picking up the 3/8" self-drives for as cheap as about 20 cents, I think. Drivers could be custom made from 3/8" grade 8 bolts, and then epoxied into a large screw driver handle. But, they are actually quite strong in concrete and limestone. The Phillips brand "Red Heads" as they were called back then were rated in concrete construction at about 4,100 lb. shear and pull out both. So, these were seen as a very viable application during that period of times, and were thought to be quite strong, as long as the placement wasn't botched! One needed to be mentored in the usage of these Red Heads, and this training was a proud moment, indeed. I don't remember hearing of any failures due to this system that seen by far the most usage, again, in limestone caves. Sometimes monster 1/2" or even 5/8" self-drives were installed if more depth and diameter was needed because of the chossyness of the rock. These could be rated at something like 9,000 to 12,000 lb. in 5,000 P.S.I. concrete. The rock was the weakest link, no doubt, and they were placed in often very wide main anchor belays for the redundancy.
They needed a certain intuition as to the depth to drill the things or you could have them protruding from the hole after you had set them, very embarrassing moment, indeed. It was better to measure and mark the inserts with a vibrating metal etching pen, or the like, but even the bottom of the hole needed to be carefully monitored to make sure that a cone of un-drilled rock had not been left in place, or any debris of any sort.
There is a way to extract these inserts by making a makeshift, sort of like, internal gear puller. You need to cut at least 2-3 pieces of grade 8 - 5/16" round stock off of a long bolt. These need to be of about 1/4" length to about 1/2" length. Then after filing the thread stock off of these little plugs you drop the shortest one into the insert first and then follow it with a modified cap screw that is about 1/2" longer than what it can possibly be. This modification needs to be done to the nose of this grade 8 cap screw by filing or grinding the threads off of about the first 1/2" of it. A little bottle of liquid wrench will be found to be very useful to start the process. It a pretty simple little kit to build,have, and use with a little bit of patience.
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two-shoes
Trad climber
Auberry, CA
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Mar 30, 2015 - 11:42am PT
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Wow! Did I kill this thread again!
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labrat
Trad climber
Erik O. Auburn, CA
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Mar 30, 2015 - 11:50am PT
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"Did I kill this thread again?"
lol
I always feel that way as well when I post and nobody responds. This is a good topic. I hope it keeps going as I'm learning from it.
Erik
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steelmnkey
climber
Vision man...ya gotta have vision...
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Mar 30, 2015 - 04:40pm PT
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Here's some of the self-drive arsenal from back when we used to place them.
L to R:
* 1/2 inch self drive bolt w/cone.
* Older holder all mushroomed out with 3/8" self-drive on it.
* The "next" holder (mushroomed but can't see it), which was stainless 3/8" rod with thread on the end and pvc grip. Seemed to work okay.
* 1" Titanium holder with threaded rod interface to bolt. A friend of mine made that for me at work one day because he got bored. :-)
Never really missed giving up on these and going to the Pika and Hurricane drills that held regular SDS bits and started using Rawl 5-piece bolts.
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Roger Brown
climber
Oceano, California
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Mar 30, 2015 - 07:04pm PT
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The one's on Rixon's had the type of bolt that were made to have the head snap off so there was nothing to get a wrench on. I had no idea what I was trying to pull till I got one out in one piece.
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two-shoes
Trad climber
Auberry, CA
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Mar 30, 2015 - 07:35pm PT
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Yeah, Steelmnkey. Nice looking homemade drivers. Poor mans drivers! Where did you use these drivers?
I like 36 volt Bosch compact now! 6 lb. Drill all day long 15 seconds a hole and with precision.
Roger Brown. Yeah, those were those self-drive snap-offs. They would snap off irregular and with a sharp edge on top. I think you were suppose to set them and just snap off the top with a twist of your driver. All of these set ups are inferior in granite, though!
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two-shoes
Trad climber
Auberry, CA
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Mar 31, 2015 - 04:47pm PT
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I had no idea that I could just knock stuff completely dead!
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PaulR
Trad climber
Bishop, CA
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I'm going to make a guess as to why these button heads break. JUST A GUESS! The split and deformation in the shaft is produced while the metal is very hot, red hot, and very ductile. The button head is then heat treated to harden the metal and lock in the deformation. This is why there are few stainless button heads, heat treatable stainless is expensive. This process makes the metal stronger and more brittle.
I'm going to speculate that as the bolt is driven in the force required to continue increases until the split section is fully in the rock, but the head is still sticking out. At that point you are hitting with maximum force. Any hammer blow that does not hit straight along the shaft will add a bending moment and possibly initiate a fracture. Remember the metal is brittle. Continued pounding can increase the fracture, but the the bolt will continue to go in.
The position of this bolt's fracture looks to be at a point where the insertion force has become maximum. It could be that one awkward hammer hit is all it takes to damage the bolt.
Many bolts can go for many years without a lead fall to test them. This may have been the first time anyone hung on that bolt.
Paul
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two-shoes
Trad climber
Auberry, CA
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PaulR,
Great guess! Your close. Try again!
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Roger Brown
climber
Oceano, California
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Paul,
Most, if not all the ones I find, have the break about at the half way mark on one side only. The split is always at the bottom end of the bolt. (a 3" long bolt or a 1-1/4" long bolt it is always at the bottom). The split is only near the top end on a short 1-1/4" bolt. Your point is well taken though, as it sure makes sence. I have at least 2500 bolts with thier hangers bagged and tagged here. It would be interesting to see if the cracked ones show signs of damage from off center hits. This season I will start putting the cracked/broken ones in a separate container. I will be replacing mostly 5/16" button heads this season.
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Urmas
Social climber
Sierra Eastside
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Please humor my ignorance here, but I thought that split shaft bolts were ductile and springy, not brittle. Compressing the split would cause the expanded parts of the shaft to press against the walls of the hole like two leaf springs. This is what keeps the bolt from coming out. If the act of driving them in, caused stress fractures or points of weakness, it would call into question the very design of these bolts. And if the design is so inherently flawed, why haven't more of them failed?
Maybe there is enough variation in the manufacturing process to account for some weaker than normal units. I suppose it's a good thing each piece of climbing hardware is individually tested, unlike construction fasteners.
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two-shoes
Trad climber
Auberry, CA
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Urmas,
I think you're asking the right questions.
I had talked to Ed Leeper on more than one occasion about his hangers, and about problems in Rawl-drive 1/4".
Ed was so knowledgable on all of these materials one would have thought he might have been a materials scientist, or at the least, a metallurgist. He assured me he was not. But, he had a friend who was a metallurgist. He could really talk this stuff. I had only taken high school and Jr. college level metal shops and welding shops, a little bit of Applied Physics. But, I have long had a general interest in bolting techniques.
Ed had told me that they were discovering through time that all of these hard metals, chrome-moly pitons, hangers, and even Rawl-Drive compaction bolts, that are indeed like spring steel alloy, if they were put in a bent configuration, that in time, stress fractures would slowly happen. These can be microscopic, at least at first. And then corrosion will chase these clean little fractures and soon rust through. The corrosion was governed by how much moisture was present, but also governed by and dependent on things like acidity, and even the ozone which is more abundant at the very top of the inversion layers. If you think about this idea and study these old bolts and hangers with the aid of 10 power magnification, I think it becomes apparent that this is the probably the main cause. There may be other factors that are unforeseen as well.
I believe this is what he was laying out to me over 24-25 years ago when we were just first starting to have Leeper hanger troubles. I remember him saying that he had originally designed the Chrome-moly Leeper hangers for aid only, and with the idea of a dynamic hip belay only. He reiterated that they had never been thought to be used with a belay plate, or even for use as for free climbing.
25 years ago nobody could imagine that 5/16" Rawls would ever experience this problem. I felt this was eventually going to happen, I just didn't think it would be a problem this soon.
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PaulR
Trad climber
Bishop, CA
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If the material is too ductile the shaft will conform to the hole and lose the spring required to keep it from pulling out. The split is put into the shaft when it is ductile. One poster indicated that tapering the top of the hole is supposed to be part of the installation. A taper would help to distribute stress from off axis hammer blows. Stress fractures require an event to initiate a small crack, maybe microscopic, they take time to form. The micro crack also needs to be in an area of sustained stress. This bolt broke near such an area.
There are multiple ways for these systems to fail, this is a suggestion for this accident.
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two-shoes
Trad climber
Auberry, CA
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Paul,
That sounds correct. You're correct about the bevel on the top edge of granite. The harder the granite, the easier it is to dinner plate the surface. It's a lot like hard clear ice is when trying to strike it too hard with the ice tool. Softer rocks, not as much need for the bevel or chamfered edge.
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Greg Barnes
climber
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Topic Author's Reply - Apr 2, 2015 - 02:51pm PT
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Here's some info on the current version of the buttonhead (the Powers "Drive" bolt). I don't know if everything is exactly the same as 25 years ago before Powers bought Rawl (and now Black & Decker has purchased Powers):
Anchor Body: Heat Treated AISI 1018
Zinc Plating: ASTM B633, SC1, Type III (Fe/Zn 5)
That's from here:
http://www.powers.com/pdfs/mechanical/03601.pdf
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Roger Brown
climber
Oceano, California
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Greg,
Thanks for that link. I was asked long ago "why 10 diameters from the old hole" and I said I didn't know for sure, but that is what I do. Maybe you told me or I learned it as a construction worker. Replacing 5/16" and not able to use old hole means 3-1/4" from the old hole to the new hole. Good stuff to know.
Edit: Replacing 5/16" with 3/8" means 3-3/4" I guess at 4" (wrench length)
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Greg Barnes
climber
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Topic Author's Reply - Apr 2, 2015 - 03:46pm PT
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Roger, most bolters use well more than 10 bolt diameters from other bolts (less than 4" looks way too close to most climbers particularly with 2 anchor bolts), although in good granite you could probably do less than 10 with no problems.
I'm a bit leery of a blanket endorsement of the (concrete) 10 diameters rule without considering all the factors of the placement, particularly horizontal planes in sandstone or other relatively weak rock. Even granite can have bands/fracture planes/etc.
Anyway here's an example of the kind of thing that can happen if you don't consider weak rock:
http://www.mountainproject.com/v/106570866
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PaulR
Trad climber
Bishop, CA
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1018 steel is medium a carbon (.18% C, balance Fe) steel. It can be heat treated, but not to the point of being like glass. Very common stuff. The plating is easily scrapped off.
A crack can also grow from stress cycling due to temperature cycling. This could lead to fatigue failure. The rock and the bolt expand at different rates. 9125 days is not that many cycles, unless the stresses are high. Of course, hanging and a few falls would accelerate the process.
Paul
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two-shoes
Trad climber
Auberry, CA
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Roger,
That old adage about 10 bolt diameters from the nearest hole is for concrete, and construction work, and doesn't necessarily apply in a life and death situation. I usually go at least 10" from the nearest hole, and sometimes farther when in doubt (especially if there are any apparent cracks close by).
There have been a few instances of 2 bolt belay rock chunks just calving off taking the climbers with them. Why not go with a less risky strategy? The pressure that a bolt exerts within the rock, I believe, can sometimes make small stress fractures below the surface of the rock, working larger in time. 20 and 30 years ago it was more common to separate the belay anchors as much as 2 feet and wider. This came about after single bolt anchors had failed taking sometimes the 2 man team down with it.
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SuperTopo on the Web
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slow to drill in hard rock
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