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  #1  
Old 12-23-2011, 01:29 PM
Lemmingman's Avatar
Lemmingman Lemmingman is offline
 
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Default Bolt Torque question

Im attaching the bell crank brackets, W-823PP. The AN3-6A bolt threads into a K1000-3 nutplate.

The bolts are threading in smoothly and gets stiffer as I get closer to the bracket that I'm bolting on. I get the bolts to the point where they and the washers are just touching the bracket. When I get my torque wrench (set for 23" lbs) out for the final fit it "clicks" immediately without tightening it any further. The bolt appears to be tighter than 23" lbs even before I get to the bracket. I've even backed the bolt out to where the washer could freely spin and the torque wrench does the same thing. Obviously having a tight nutplate is good, but isn't this over-tight? Have you run into this before?
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  #2  
Old 12-23-2011, 01:38 PM
sstellarv10 sstellarv10 is offline
 
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Default

I've found that all the bolts that are screwed into nutplates tend to torque out before seated, I don't bother using the torque wrench with nutplates anymore, I just go by feel. I believe there was a thread a while back about this same issue.
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  #3  
Old 12-23-2011, 01:39 PM
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Default What I did...

Remove the bolt, lube the nutplate with a bit of beeswax or Boelube, and try it again.

Like Stein always says, just my $.02
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  #4  
Old 12-23-2011, 03:03 PM
CMW CMW is offline
 
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Default

This is where a beam style or indicating style torque wrench is handy. You need to measure the friction drag torque due to the self locking features of a locknut or nutplate. This drag torque should be added to the recommended torque for the fastener. For example, for an AN3 nylock nut, the drag torque is normally 5-7 in-lbs, so the final torque should be 26-31 in-lbs.

This comes from AC43.13 7-40d.

Using a little beeswax or boelube and running the bolt in and out a few times is a good idea. If you have an indicating style torque wrench and you do this, you will see the drag torque decrease a little each time until it stabilizes at a value. Use that value to add to the recommended torque for the fastener.

Just one more thing to keep in mind.

-Chris
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  #5  
Old 12-23-2011, 03:12 PM
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Mark12A Mark12A is offline
 
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Default Bolt Torque

We would occasionally run into this problem where the running torque was quite high. It may very well be caused by poorly cut threads or gunk on the threads. I'd suggest chasing the threads...we would use an out-of-calibration thread plug, but running a threaded insert in and out a few times often does the trick. Also, if the threaded insert part is slightly out too big (not unlikely, given production variances) you'll have higher running torque.

An aside...friend from Teledyne Continental told me they would cut the plug threads oversize so the spark plugs could be hand-threaded per their customer demand. In some cases, a very good set of taps and dies may be a good idea to keep around.
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  #6  
Old 12-23-2011, 03:14 PM
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Av8torTom Av8torTom is offline
 
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Default Calculate

You should be able to calculate how much torque the drag is creating by increasing the setting on your wrench until it just stops clicking off, then add that value to the 25"lbs and that should be you final torque setting. You'll have to do that for each bolt

T
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  #7  
Old 12-23-2011, 03:24 PM
vtfast vtfast is offline
 
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Default Running torque

All self locking nuts or nut plates have what you call a running torque. Once you get the bolt at least one thread into the self locking device you should see how much torque is applied to the bolt to make it turn. Add this torque to the final torque and you will end up with the correct finishing torque

Bolt running torque equals let's say 12 inch pounds,
Final torque equals let's say 32 inch pounds,
Final running torque will be 44 inch pounds.

Unless otherwise stated a wet torque ( bo lube ) is not recommended, doing so you may end up over torqueing the fastener.

Just running a fastener in till German torque is met is also not good or recommended. Over stressed fasteners lead to failure. Under torqued fasteners lead to things coming from together.

At any rate, that's my 2 cents worth.
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  #8  
Old 12-23-2011, 03:42 PM
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DonFromTX DonFromTX is offline
 
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There is such a thing as a bad nutplate. I have had a couple of them so far, the bolt would go a ways and strip off the threads of the bolt, leaving you in a real pickle! I got to running the nutplate up on its bolt before attaching the nutplate after that. Had to diamond saw in a dremel tool the bolt off to get the nutplate out On most non critical torque places, I use a drop of Boelube on the screw first time in it.
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  #9  
Old 12-23-2011, 04:19 PM
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Default

Hmmm... maybe thats why I find so many undertorqued bolts. If the bolt is not applying the appropriate "clamp-up" force than your torquing process is not accomplishing the intended function (clamping the pieces together with 'X' amount of force).

Always make sure that a bolt is actually tight in the hole (bolt won't spin in the hole and the washers are locked in place) before you consider it "torqued". I find lots of loose bolts with spinning washers (this is a quick check for looseness or grip length to long).
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  #10  
Old 12-24-2011, 08:56 AM
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Lemmingman Lemmingman is offline
 
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Default

Thanks for all the answers. I'd never heard of "running torque", so this was a new tidbit for my brain.

I had read AC43.13 7-40d but had not put 2 and 2 together to realize they were describing what I was experiencing.
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