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  #11  
Old 02-16-2013, 08:34 AM
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Toobuilder Toobuilder is offline
 
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I was also surprised at the relative low tension of smaller fasteners when I went through initial technical training in the Air Force. Since that "calibration" many years ago, I now reserve the torque wrench only for critical fasteners.

In fact, we used to challenge each other to see how close we could get with the "calibrated elbow" and most of us could get within a few percent.
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  #12  
Old 02-16-2013, 09:14 AM
David Paule David Paule is offline
 
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A fastener only has so much strength. If you think about it, it's really only got so much strain energy that it can withstand before it fails. If you load too much on to it by overtorquing, then the amount of load it can carry is reduced.

Torque does two significant things to a bolt. It clamps the parts together, helping to carry shear, and it applies a tension load that the bolt can carry before it gaps. That helps the fatigue life of the bolt.

Bottom line -- torque using a torque wrench, to the specification.

Dave
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  #13  
Old 02-16-2013, 09:44 AM
DaAV8R DaAV8R is offline
 
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Default Torque

Just for fun, put a AN3 in your vice and tighten to failure or to the point it begins to yield. It takes a lot. I like the little snap-on 1/4 drive stubby rachets for these little bolts. Using the correct wrench, it seems unlikely that the bolts would be over torqued to any significant degree.

In the steel business we calibrate our bolt installation procedure on a daily basis. Torque is an indirect method of measuring tension. It doesn't take long to figure out that torque is variable based upon thread cut, lubrication, manufacturing tolerance and many other factors. I have always suspected that the torque/tension relationship for small fasteners varies more than we often realize.

Here is a device which measures tension in large fasteners. While the info on the site is not directly applicable to our fasteners, it may be interesting to some. I have always been surprised that someone doesn't offer tension control bolts or washers for other industries.

http://www.skidmore-wilhelm.com

I do agree that all critical fasteners should be installed with a TW as this is the best tool we have in most cases.
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  #14  
Old 02-16-2013, 09:55 AM
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Don, don't you ever sleep?
Are you comparing my schedule to those on the "wrong" side of the world?
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  #15  
Old 02-16-2013, 10:07 AM
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Default Torque Wrenches

Now that we all agree that we should use a torque wrench probably more than we do - any good suggestions for good torque wrenches? Some of the new digital units look amazing, but probably a bit of overkill for our application.
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  #16  
Old 02-16-2013, 10:30 AM
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Default Torque wrenches

I've had my two torque wrenches, 1/4 and 1/2 inch click type for about 40 years. I have always stored them at their lowest torque settings but they have not been calibrated since I've had them. Should they be ok or should they be calibrated periodically. I know in the Air Force our torque wrenches were calibrated quite often.
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  #17  
Old 02-16-2013, 11:20 AM
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I wonder if any one has lost a control surface in flight, due to improper Tq, that would be my biggest concern with these tiny fasteners.
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  #18  
Old 02-16-2013, 04:33 PM
lorne green lorne green is offline
 
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Quote:
Originally Posted by rv8ch View Post
Now that we all agree that we should use a torque wrench probably more than we do - any good suggestions for good torque wrenches? Some of the new digital units look amazing, but probably a bit of overkill for our application.
I use the click type of inch pound torque wrench. I wish I would have bought a dial type instead. It gives you some indication of how close you are to you torque goal.
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  #19  
Old 02-16-2013, 04:37 PM
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I bought a Parktool TW-1 inch-pound wrench. 1/4" drive with a 3/8" adapter. It's apparently used mostly for bicycle work, but I think the in/lbs are the same on an airplane. Anyway, it was FAR FAR less expensive than most of the alternatives, dial or click. I paid under $40 shipped for it, brand new. There's a bigger TW-2 as well.
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Last edited by DaleB : 02-16-2013 at 05:06 PM.
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  #20  
Old 02-16-2013, 05:04 PM
mcencula mcencula is offline
 
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Default Torque vs fastener size

Years ago I read a paper on bolted connections. It indicated that when torquing by "feel", small fasteners tend to be over torqued and large fasteners tend to be under torqued. The rationale given is that humans tend to scale things up linearly (i.e. a 1/2 inch bolt should be torqued twice as much as a 1/4 inch bolt), but the bolts themselves follow an exponential curve.

I always use a torque wrench.

FYI, an over torqued bolt will have less shear capability than a correctly torqued bolt.
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