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Torquing Bolts

D

dsm8

Well Known Member
Patron
Good evening:

What do people use for a torque wrench. I am using a 1/4" click type and am deathy afraid of under and over torquing. While using the nuts with the nyon inserts it feels like it needs more torque than is reccommended. I read some where that you need to add the torque requried to turn the bolt or nut to the reccommended torque setting. With a click wrench how do yo figure this out. Any advice would be greatly appreciated.

Thanks

Don
emp/tailcone 80% done
fuselage arrived two days ago
 
Torque wrenches etc

There is an excellent manual available on the FAA.GOV web site. It is the FAA-8083-30 general maintenance technician handbook. Chapter 9 is about tools and how to use them
 
further on torque

For self locking nuts using the insert the "running" torque must be determined. that is the torque that is required to move the nut after the threads engage in the insert. The above mentioned handbook covers that as well
 
Determining Run On Torque

I agree that adding Run On torque to the desired torque is the most accurate way to torque a fastener. However, for AN3 and AN4 fasteners the run on torque is usually very low - so low that most of us don't have a torque wrench that reads low enough to measure it. For example, my 1/4 drive CDI torque wrench starts at 20 in lbs.

There is a CDI electronic (click type) torque wrenches that starts at 2 in lbs but this wrench costs almost $400.

ATS carries a nice 1/4" dial torque wrench with a scale of 0 - 75 in lbs. This is probably the best tool to measure run on torque but at $230 it's not cheap. Maybe I'll buy one some day.

For now, I just torque the self-locking nuts to the high end of the range specified in AC 43.13 (i.e. 25 in lb for AN3)
 
I usually torque to the high end of the range with lock nuts reasoning that the running torque is likely less than the spread between max and min.

If the bolt is in shear it shouldn't be as critical since the forces don't tend to loosen the nut. It's the bolts in tension like landing gear and props I am particularly careful with it.
 
For the smaller torque values, like measuring the resistance once the bolt goes into the threads, I bought a torque wrench from a bicycle store. It was a 'Park Tool' Model TW-1 and ran somewhere around $50.

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Bob
 
Just remember that the objective is to put the bolt in tension, and torque on the nut is an indirect method of estimating how much tension is on the bolt. Things like a drop of oil on the threads, or a dinged thread, or even the correct thread length protruding through the hole will alter the relationship between bolt tension and torque. If we could see the data from a strain gaged bolt vs. torque, we'd probably throw our torque wrenches away. But the wrench provides the best measure that we have at an economical price.
 
RFSchaller said:
If the bolt is in shear it shouldn't be as critical since the forces don't tend to loosen the nut. It's the bolts in tension like landing gear and props I am particularly careful with it.
Click to expand...
Which model of RV's have the landing gear bolts working in tension? All of them that I have worked on are working in double shear.
 
By writing my post last night, I talked myself into a new torque wrench. :) I found a brand new Proto 0 - 75 in lb dial wrench on ebay for $100. I bought it this morning.
 
Where is the creativity?

For guys that build airplanes, you aren't being very creative :)

If you have a box end wrench, a scale and/or a little bit of weight you should be able to figure out the drag of the nut.
 
Jesse said:
Thanks. I assumed it was something like that. The 6, 7, 9 and 10 are all in double shear.
Click to expand...
We don't get NO respect. ;) All -8 attach bolts are in tension. You have shear, you have big problems.
 
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It looks to me like all the forces on the RV-12 landing gear attachment bolts are tension.

I understand the preload concept for keeping the nut in place, but we use lock nuts that should prevent backing off. I'm not saying don't torque! I just have some concern about preloading too much when the structural forces also increase the tension. That's why I like bolts in shear.
 
The actual torque used on the 10-32 and 1/4-28 bolts is much less then you would likely use when just using a wrench and tightening by "feel"
 
Bob,

Yes the preload is on the bolt but it creates a force between the bolt and nut threads so that friction will resist the tendency to back off. My point was that the preload is additive to the structural forces when the joint is designed with the bolt in tension rather than shear.

Rich
 
bolt is now longer

When a bolt is torqued to its proper value the bolt is now longer then it was and is now at the working strength and length of the bolt. The bolt. will not get longer until the design working strength is excited.

If the bolt gets longer then its design length the part moves and or bounces, this can also happen if the bolt is not at its working length (stretch) ,this is what happened when the landing gear bolts were not torqued to the right value


RFSchaller said:
It looks to me like all the forces on the RV-12 landing gear attachment bolts are tension.

I understand the preload concept for keeping the nut in place, but we use lock nuts that should prevent backing off. I'm not saying don't torque! I just have some concern about preloading too much when the structural forces also increase the tension. That's why I like bolts in shear.
Click to expand...
 
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