Seriously? Do you need a torque wrench for bolts?
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I thought I'd start a new topic - in a previous thread - several were suggesting using a torque wrench, else you basically snap bolts off by tightening them. |
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Its not that hard to snap off the head of a 3/8" Powers 5-pc. cap bolt, all of my friends (and myself) have done it. Thats the main reason I prefer Hilti Kwick-bolt wedges. |
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here is a nightmare i will plant in your head... whats worse than snapping the head off by over-tightening, is to over-tighten to just past the yield point. |
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Just some quick joint engineering to shed a little light on bolts. The engineering in a bolted joint is kind of counterintuitive, at least it was for me. I always had thought the strength was carried directly by the bolt, but in a properly tensioned joint, it isn't. |
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well put, Larry. |
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Dan Brayack wrote:I was under the impression that torque and bolt tension have no direct correlation - say you tighten two bolts to 10 ft-lbs or whatever. the bolt tension will be drastically different since nut friction is a significant contributor to torque resistance and never constant. -DannoThe nut/bolt friction is important, but should be fairly constant for a given bolt manufacturer and with similar materials, and even then, should be able to be calculated based on knowledge of your fasteners. It is taken to account in calculating the bolt torque. This is why the torque is valuable and used all over the place in industry for quality control, esp for vital joints such as in automobiles/aircraft. You can see some basic formulas here. But I would follow the manufacturer's advice, as they'll have done empirical testing to determine the bolts K-factor and proof strength. I think the less controllable factors such as the the strength of the stone, the angle of the hole, how well the bolt meets the rock all play much more important roles than how precisely tightened the bolt is, and further, that modern bolts are very strong even in shear. So long as you don't tighten the bolt to the point where it starts to yeild/break, I think there's a good margin of safety. - Note - I've never placed a bolt, so i can't speak from experience, but i am an mechanical engineer and climber. |
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Larry S is pretty much spot on about how it should work. Of course, there is a fair amount of variation in the field - anywhere from properly tightened bolts taking most of the shear load in friction,to bolts that aren't tightened at all and take the shear load in bearing. |
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I've been an aircraft mechanic for 25 years; I've torqued a lot of bolts- some to tens of thousands of ft/lbs. In engine manufacturing, some bolts are not torqued, per se, but actually stretched to a specified tolerance. Obviously, there are variables involved with holes in rock that can't be practically controlled; but it has been my experience, some of it very hard won, that torque specs are important. (As for the question of tightening friction in the nut, determine the "running torque", use a deflection torque wrench, not the compression kind, they're cheaper any way. Add the running torque to the specified torque for the final value.)I'm not saying that you should carry a torque wrench on a big wall in the back country. But, if your setting a quality sport route, and you're carrying a drill motor anyway, add the minor weight of a torque wrench, and use the specified torque. A job worth doing, is worth doing right, as they say. |
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Unless you are extremely weak and using a tiny wrench, tightening as hard as you can is seriously over torqueing. I suggest you use a torque wrench some and feel what the suggested torque feels like. 20 lbs is not very much. |
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Seems like at a minimum, it'd be a good idea to borrow a friends torque wrench and get a good feel for what 60, 80, 100 ft-lb feels like, so you in the ballpark of whatever is spec'd. I don't think tightening 'as tight as you can' is a good idea, unless you're using a really short wrench... but testing with a torque wrench will let you know for sure. |
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GREAT THREAD! (EDIT: pun intended) Larry S wrote:I think the less controllable factors such as the the strength of the stone, the angle of the hole, how well the bolt meets the rock all play much more important roles than how precisely tightened the bolt is, and further, that modern bolts are very strong even in shear. ... - Note - I've never placed a bolt, so i can't speak from experience, but i am an mechanical engineer and climber.hole angles and how the hangers sit are some of the easiest things to control (yes, even on lead), and some of the more important variables to maximize strength/longevity. but suprisingly often neglected! |
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Dan Brayack wrote:In response to the claim that "I can break off a bolt with a hand wrench" I would pay to see that...oooo how much???? |
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M Sprague wrote:I suggest you use a torque wrench some and feel what the suggested torque feels like. 20 lbs is not very much.while youre out calibrating yourself to the specified torques, also note how many turns of the nut it takes past finger tight.... the turn-of-the-nut method can be very repeatable, assuming you keep track of how worn your drill bits get... |
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the last post, in the wrong context, is likely to have your system administrator calling the cops.... |
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Dan Brayack wrote: I've placed maybe 400 bolt or so and every one of them, I've just tightened them as tight as I could. <3 -DannoDoes this worry anyone else? Over-torquing is one of the best ways to remove bolts. They usually shear off at least an inch or so deep and then you can patch the hole. Trust me, I'm a doctor. |
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Price wrote: Does this worry anyone else?yes if: 1)i ever climb in west virginia, or 2)i think about it too much. which, btw, i am guilty of #2 quite often, and sometimes can hamper my "go for it" attitude when i play the "whats behind that hanger"- game. EDIT: come to think of it, over-thinking is my biggest weakness in climbing in general. |
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Darren Mabe wrote: yes if: 1)i ever climb in west virginiaThat wasn't my problem last time i was down there, got on a route at the new with maybe 8 bolts... At least half of them were only hand tight/spinners. |
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Price wrote: Does this worry anyone else?Yes. Until you have a very good feel for what different amounts of torque feel like (learned from using a torque wrench), then use a torque wrench when you are bolting. I remember the first time I used a torque wrench (on my truck)...I was hugely surprised as to how much I had been over tightening bolts. As Mark S. says, 20 lbs. isn't much. |
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Larry S wrote: That wasn't my problem last time i was down there, got on a route at the new with maybe 8 bolts... At least half of them were only hand tight/spinners.yikes! |
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I'm a structural engineer (have my Masters in Bridge engineering and had a couple steel classes) |
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J. Albers wrote: Yes. Until you have a very good feel for what different amounts of torque feel like (learned from using a torque wrench), then use a torque wrench when you are bolting. I remember the first time I used a torque wrench (on my truck)...I was hugely surprised as to how much I had been over tightening bolts. As Mark S. says, 20 lbs. isn't much.also keep in mind that many torque wrenches are longer than the regular wrenches used to install bolts... hence the "feel" will be different. this is why i mentioned the turn-of-the-nut method above, along with a torque wrench... |