Seriously? Do you need a torque wrench for bolts?

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.

I've placed maybe 400 bolt or so and every one of them, I've just tightened them as tight as I could. 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.

Its also been my experience when breaking off bolts, that with a 2 foot breaker bar, its a major pain in the butt - its basically all my strength to break even old rust bolts off. New bolts are really a major pain to break off...spinners are the worst and generally the easiest to break off since the spinning action of the hanger knocks the fresh rust off a bolt - allowing more rust (rust on the outside protects fresh steel on the inside - check out some highways bridges - they're made of weathering steel which rusts immediately then seals)

Granted I'm placing 3/8 2-3/4" bolts into extremely hard sandstone...

In response to the claim that "I can break off a bolt with a hand wrench" I would pay to see that...

<3

-Danno

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.
But as far as torque goes, its not that hard to determine whats tight enough.

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.

oh, and Mike, +1 on the Hilti KB3s!

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.

The short explanation is that the strength in a properly tightened joint is not seen by the bolt until you overcome the preload (in tension), or the friction of the joint (in shear). Most climbing bolts are loaded in shear, so the friction in the joint is very important. (friction is a function of the preload)

A way to visualize this is picture two wood blocks with a rubber band wrapped around them holding them together. If you try and pull them apart, until you overcome the tension in the rubber band, they don't move, and the rubber band doesn't see any more force until the joint separates. If you try to slide them, until you overcome the friction that the tension in the rubber band helps make, they don't move. If you use a tighter rubber band (smaller circumference), the joint is stronger, even though the rubber band is still the same strength.

The bolt is the really a spring (or a rubber band), it does stretch when you tighten it. Once you load it over the preload tension, you are now directly loading the bolt. That is why a "spinner" bolt is so much weaker in shear loading, you don't have the friction in the joint to take the load. (spinner hangers can also torque load the bolt)

All that said, I don't own a torque wrench, and I don't mind you tightening bolts by feel, though i wouldn't hassle someone who recommended the use of one.

well put, Larry.

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. -Danno

The 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.

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.

add me to the list of people who have overtightened a 3/8 5-piece with a tiny wrench and busted the hex head off. that is a real 'Son of a b!&tch!!!!" moment. i have also seen busted off hex heads at the base of a couple routes. like wiledhorse pointed out though, the worst is leaving a time bomb for somebody else.

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.

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.

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.

I've never placed bolts, but was thinking I'd read there are some concerns about over torquing with soft sandstone? That could be hogwash -- someone else might be able to confirm.

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!

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????

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...

the last post, in the wrong context, is likely to have your system administrator calling the cops....

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 -Danno

Does 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.

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.

Darren Mabe wrote: yes if: 1)i ever climb in west virginia

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.

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.

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!

I'm a structural engineer (have my Masters in Bridge engineering and had a couple steel classes)

I think that a 5 piecer and a wedge bolt are two completely different stories and it makes sense that you could snap a 5 piecer - since their rod length is significantly smaller than a wedge!

So rephrase, I'll give you my wrench and see if you can break off a wedge bolt in our sandstone.

Consequently, I think under tightening is a major problem because spinners are annoying and can get you into trouble...if your hanger falls off - you're hosed....

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...