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Torquing AN3 bolts

P

prkaye

Well Known Member
I was installing bolting the inbaord hinge-bracket/bearing assembly to the rear spar of the HS today. The plans called for AN3-5A bolts, AN960-10 washers and AN365-1032 nuts.
These parts weren't labelled explicitly in the stuff from Vans, but there was a bag which was labelled in the parts list as "AN3 Hardware". Inside I found bolts washers and nuts. I verified the bolts to be AN3 with my bolt gauge and selected ones with a length of 5.
Questions:

1) Were these the right bolts? What does the final "A" mean an AN3-5A ?

2) The nuts in the bag were all identical, they all had white plastic inserts in them. Are these the AN365-1032 nuts?

So I went ahead and used these parts. I set my torque wrench for 20in-lbs, and began to tighten them. The torque wrench never released (although I've never used a torque wrench so I'm only guessing what this would feel like. What happened was that the nuts eventually got to a point where they turned sort of freely, without tightening on the bolt anymore. This made me wonder...

3) Do these nuts somehow self-torque with those plastic inserts? Should I be worried that they stopped tightening before 20 in-lbs, when the guidelines say AN3 bolts should be torqued to 20-25 in-lbs?

If I'm correct in my hypothesis about the nuts self-torquing, one more question...

4) How much damage to those nuts can result if I keep turning them once they have stopped tightening? Should I replace them?

Thanks!

Phil
 
I can't help you with the ID of those bolts except that the "A" indicates the bolt is not drilled for a cotter pin, but I can offer some advice. IMHO when in doubt, redo it. Bolts are cheap and it's worth the piece of mind. When it come to torque wrenches, I posted this several times. Grainger.com sells a dial type torque wrench made by Proto. All you have to do is look at the dial and you know what the torque is. I would not trust my ears to hear a "click" from a standard wrench, when you are dealing with the low torque settings in the airplanes, it may not "click". When you set the torque you must factor in torque drag. That's created by the friction between the bolt and the nylock nut or nutplate. This amount is to be added to the torque specified for the particular hardware you're using. It's figured by running the nut down to where it almost touches the surface. The Proto wrench I use, has a blue needle which you set to zero. Turn the nut about a half turn and see where the blue needle stops, the nut should still not be tight to the surface. Then add that that amount to the torque spec
ie; 20-25in lbs + 5in lbs=25-30in lbs. I'm not sure what you mean about the nut stop tightening. It should tighten at and beyond the torque setting. These bolts are not "self-torquing". The plastic insert only serves to keep the nut from backing out. Also mark your torqued bolts with torque seal so that during you inspections you can confirm your bolts haven't loosened.
 
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prkaye said:
I was installing bolting the inbaord hinge-bracket/bearing assembly to the rear spar of the HS today. The plans called for AN3-5A bolts, AN960-10 washers and AN365-1032 nuts.
These parts weren't labelled explicitly in the stuff from Vans, but there was a bag which was labelled in the parts list as "AN3 Hardware". Inside I found bolts washers and nuts. I verified the bolts to be AN3 with my bolt gauge and selected ones with a length of 5.
Questions:

1) Were these the right bolts? What does the final "A" mean an AN3-5A ?

2) The nuts in the bag were all identical, they all had white plastic inserts in them. Are these the AN365-1032 nuts?

So I went ahead and used these parts. I set my torque wrench for 20in-lbs, and began to tighten them. The torque wrench never released (although I've never used a torque wrench so I'm only guessing what this would feel like. What happened was that the nuts eventually got to a point where they turned sort of freely, without tightening on the bolt anymore. This made me wonder...

3) Do these nuts somehow self-torque with those plastic inserts? Should I be worried that they stopped tightening before 20 in-lbs, when the guidelines say AN3 bolts should be torqued to 20-25 in-lbs?

If I'm correct in my hypothesis about the nuts self-torquing, one more question...

4) How much damage to those nuts can result if I keep turning them once they have stopped tightening? Should I replace them?

Thanks!

Phil
Click to expand...

The A is a hole-less (non-drilled) bolt (no provision for a cotter pin).
AN365-1032 nuts have different colored inserts depending on the manufacturer. They are a 3/16 nyloc nut. Nothing self torques. You've destroyed the nuts and bolts. Please get someone to help you.
 
Info is at your fingertips

Before you get to far I would suggest you read through chapter Five of your construction manual.
I may be mistaken, but I believe it has all the information you need for hardware identification.
 
Phil,
The "A" suffix means "undrilled", as in no hole for a cotter key.

We can't tell what nuts were in the bag, but you can. Fiberlock nuts come in thin for shear applications (AN364) and thick for tension applications (AN365). You MUST learn to identify the difference on sight. Lacking a better reference, you could consult an Aircraft Spruce or Wicks catalog and look at the pictures.

If you used an AN364 shear nut and tried to torque it to 20 in-lbs, the threads on the bolt or in the nut will be damaged.

I assume you have a click-type torque wrench. It does not "release". It makes a little click, thus the name. If you pulled past the click, the threads are likely stripped.

Regardless, if the nuts are turning freely now, you need to remove them for a close inspection of the bolt and nut threads. If they are not perfect throw them away.

Nuts DO NOT "self torque".

Strongly suggest that you find a local TC, licensed mechanic, or experienced builder for some school on very basic shop issues. Guessing about aircraft hardware and its proper installation is a bad thing.

Dan Horton
 
How much should you torque a AN364 nut? Everything I've read does not indicate diffference in torque between 364 or 365 nuts.
 
my torque wrench

I just tried my torque wrench (Power Fist 1/4" drive torque wrench) on a spare nut and bolt just to get the feel for it... I wonder if it's not working. I tightened very hard, and no clicking, nothing discernable happens.
I wonder if it's because I got it for less than $30 (CAD) ?

How much should I spend for a suitable wrench? Do I want 3/8" drive or 1/4" drive?

Is this one overkill?

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611691126
(it's $184 USD).
 
I have a Craftsman torque wrench. It doesn't click per se so hearing it , ummm,, not click...isn't a problem.

But it "gives" a bit when it reaches the proper torque. It's kinda impossible not to feel it.

AC 43-13 is your friend.
One other thing I'd recommend. Get all your hardware out of the bags as soon as possi ble after they arrive and sort them all out into stackable bins you can buy at Ace or any other hardware store.

I also add 365 nuts and the more common bolts and washers to the order every time I make one with Aircraft Spruce or whomever. That way there's no reason not to toss a bunch of 'em in the trash if I've used them.
 
removing self-locking nuts

A related question, how do i remove those damaged self-locking nuts so I can re-do this properly?
 
AC 43.13-1B is free on the web too...

Bob Collins said:
......
AC 43-13 is your friend
......
Click to expand...

Bob is correct about "the bible" for homebuilders...
If you want a free, on-line PDF copy instead of an Amazon link, it is available directly from the FAA here:-

http://www.airweb.faa.gov/Regulator...99C827DB9BAAC81B86256B4500596C4E?OpenDocument

Hardware is covered in section 7 here.....

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2007.pdf

gil in Tucson
 
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AN364 and AN365 nuts get different torques

jlfernan said:
How much should you torque a AN364 nut? Everything I've read does not indicate diffference in torque between 364 or 365 nuts.
Click to expand...

Jorge.... check Table 7.1 in AC.43.13-1b

Chapter 7 is here...

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2007.pdf

....your confusion may be because AN365 have been re-identified (same parts) as MS20365 and AN364 ==> MS20364

They do have different torque values. You need to be careful.. the high end of the thick nuts normal torque is close to the absolute maximum for the thin shear nuts. Use of the wrong torque selection could easily damage the thin nuts and over-stress them. I believe the failure mode would be in the threads....

gil in Tucson
 
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Hi Phil,

Others have made good suggestions on the appropriate reference materials, but you might also want to "calibrate" your hands as well as the torque wrench. Even on my expensive 1/4" drive low torque "click" torque wrench, the release is very subtle at the settings used for these AN3 fasteners. Put a 1/4" hardware store bolt in your vise, set the wrench to a rather higher torque and feel for the the release/click. Lower the setting a bit and try it again, then repeat until you get down to the torque values you need, and thus know how it's supposed to feel.
Good luck!
 
I think part of my problem is that 20 in-lbs is the very bottom of the range for my torque wrench. Others have indicated that the wrenches don't work as well at the extremes of their range.
I think I may get one with a gauge... I'd find it much easier to trust a gauge reading than a subtle "click" (I was expecting a ratcheting type action after the specified torque :( ).

Twp remaining questions:

1) For a torque wrench, what's the diff between 1/4" drive, and 3/8" drive (what is the drive?). Which do I want?

2) How do I get those self-locking nuts off?

Thanks!
 
According to AC 43.13-1B, Chapter 7, Page 7-9, Table 7-1:
Torque limits recommended for installation(Bolts loaded primarily in shear)
Shear type nuts MS20364 and AN320 (24,000 psi in bolts);

An AN364 nut, thread size 1/4-28, which is what is in the kit, 30-40in lbs, max 60in lbs.
 
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The very lower end of the range is indeed the least accurate area of a given torque wrench. Ideally you would have a selection of torque wrenchs that allow you to work in the middle of the given tool's range. I have four, a 10-150 ft-lb 1/2" drive, a 20-250 in-lb 3/8" drive, a 20-150 in-lb 1/4" drive and a 5-36 in-lb "torque screwdriver" 1/4" drive. That's the one I usually use on the AN3 fasteners. I got it from Central Tool, Inc. And just as a point of reference, high quality torque wrenches tend to well on the far side of $100 each. Even the import model from Avery is about $75.
The "drive" is the square part that sticks out and is inserted into the socket. The different sizes just reflect the relative strength requirements of the range of nut/bolt sizes for a given tool - more torque requires a stronger wrench setup to handle it.
If your stripped nuts will not back off with a wrench, you may be able to get them off by using a pair of Visegrip pliers and pulling firmly while unscrewing. If it still won't come off, you'll have to grind away enough of the nut to release it. This is not fun, but a bit of careful work with a small die grinder will certainly get the job done. There are special nut splitting tools, but I 've not seen one small enough to handle the AN-3 size.
 
>> An AN364 nut, thread size 1/4-28, which is what is in the kit, 30-40in lbs, max 60in lbs.

Page 5-13 of the plans from Vans has a table. There it says
AN3, Bolt size (threads per inch) #10-32, 20-25 in-lbs. I figure it's safe to go with van's numbers??

Thanks William, for your answers to my other questions. For getting the nuts off... what about a hacksaw (I'd get new bolts too) ?
 
If your going to do alot of -3 nuts, I would go with the 1/4 trque wrench. Usualy they have a lower range of torque, usualy around 10-100 or so inch pounds. Most 3/8's start at 20 which as mentioned is not the most accurate. "the drive" is the size of the square end that the socket snaps on, naturaly the 1/4" wrenches use 1/4" sockets, etc. As for removing a nylock, just unscrew it...or are you saying to tightened it so much that it is stripped so bad that it now just spins there? If thats the case, your going to have to cut it of. Your going to have to be really carefull not to damage your HS, but I would try and cut the heads off with a straight diegrinder with a a 3" cut off wheel. Slowley grind the head down untill its thin enough to pop off. It sounds like your not familiar with how a click type torque wrench works...often there is not a click, nor does it just start freewheeling with a clutch mechanism (although there are torque wrenches of that style, usualy only used for tiny screws and such.) Instead of click, you get a slight deflection in the head of the wrench. Clamp a socket in a vice, put your wrench on it, and push it back and forth, you should be able to see the deflection. I see your in Canada, so you may be used to the metric system more so than pounds, inches, etc. But try and think logicaly about a bolts torque...25 inch pounds means one pound of force on a 25 inch long wratchet...which equals two pounds of pressure on a 12 1/2" wratchet, which is probaly close to most inch pound torque wrences. So, grab your 2 pound bucking bar and hold in in your palm...that weight is how much force you should be putting on the end of your torque wrench. For these -3 bolts, it feels like a tiny amount. In fact it is, and I have no idea why aircraft bolts get such low torque values. Typical steel hardware in the grade 5 to 8 range has 3/16" bolts torques to 60 to 120 inch pounds. I suspect that it has to do with the fact it is usualy clamping aluminum structures, typicaly sheetmetal..


prkaye said:
I think part of my problem is that 20 in-lbs is the very bottom of the range for my torque wrench. Others have indicated that the wrenches don't work as well at the extremes of their range.
I think I may get one with a gauge... I'd find it much easier to trust a gauge reading than a subtle "click" (I was expecting a ratcheting type action after the specified torque :( ).

Twp remaining questions:

1) For a torque wrench, what's the diff between 1/4" drive, and 3/8" drive (what is the drive?). Which do I want?

2) How do I get those self-locking nuts off?

Thanks!
Click to expand...
 
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Torque wrenches

Try to find a K-D brand "beam" style torque wrench as shown here in this link.

http://www.kd-tools.com/29552957.htm

It will read from zero to 60 in.lbs. of torque which is ideal for the AN-3 hardware.
Also, I haven't seen it mentioned here, but the torque has to be measured while the nut is rotating on the bolt, in other words, read the torque while smoothly tightening the fitting. A good auto parts store can probably get you the K-D wrench and they are not expensive.
 
Phil, if you have a Dremel tool, you can get a tool from Harbor Freight (assuming you have those) which is an arbor, and and 4 or 5 very small diamond cutting wheels. The wheels are about 7/8" diameter and about .020" (wafer thin).
You can carefully cut down through the nuts if you have to with this setup.
I would certainly have a thin piece of steel (tin can lid?) surrounding the nut as close as possible to avoid cutting into aluminum in case your hand isn't too steady!
The price at harbor Freight is probably less than ten bucks, and I used one wheel to cut out the "mouse hole" for the tailwheel mount with absolutely no sign of wear on the wheel! (And, no cutting wheel dust!)
 
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Thick and thin nuts....

jlfernan said:
According to AC 43.13-1B, Chapter 7, Page 7-9, Table 7-1:
Torque limits recommended for installation(Bolts loaded primarily in shear)
Shear type nuts MS20364 and AN320 (24,000 psi in bolts);

An AN364 nut, thread size 1/4-28, which is what is in the kit, 30-40in lbs, max 60in lbs.
Click to expand...

Jorge.... most of the nuts in my older RV-6A kit are AN365 - the thicker nuts - and would be torqued to 50-70 inch-lbs. for 1/4-28 per the table 7.1.

The original poster was also referring to a AN365 nut but with an AN3 bolt which is 10-32...

At the smaller 10-32 size the torque should be 20-25 inch-lbs. and a max. of 40 inch-pounds for an AN365 nut.

Are you misidentifying the hardware or thread size?

gil in Tucson
 
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DanH said:
Phil,
The "A" suffix means "undrilled", as in no hole for a cotter key.

We can't tell what nuts were in the bag, but you can. Fiberlock nuts come in thin for shear applications (AN364) and thick for tension applications (AN365). You MUST learn to identify the difference on sight. Lacking a better reference, you could consult an Aircraft Spruce or Wicks catalog and look at the pictures.

If you used an AN364 shear nut and tried to torque it to 20 in-lbs, the threads on the bolt or in the nut will be damaged.
Click to expand...

These nuts are the one's I was referring to. On my 9A they are used on the aileron bracket and the screw they attach to holds the rod bearing for the aileron pushrod. I just wanted to be sure I didn't overtorque them.
 
Torque ?-what is rolling friction of a 10-32 nyloc?

I have the expensive 1/4 in torque wrench. It works at 20# (barely, bottom of it's range).

For the 10-32 fasteners on the 9 HS (holds center bearing assembly to spar), my kit had thicker "tension" type lock nuts, so I read the torque from AC43.13 as 20-25 inch-pounds with a maximum of 40.

I had read somewhere that you should add the torque required to get the nyloc nuts to turn to the desired torque. This makes sense to me. What I couldn't figure out was what is this "rolling friction"? I couldn't measure it with any tool I own, so I "estimated" and torqed to 28 inch pounds.

BTW - I had the same issue with the counterweight hardware (same fasteners, same torque). The thin "shear" nuts on the rod end bearings torqued to 110 inch pounds and didn't have the lock nut so they were no problem.

Good luck to the original poster!



Love to hear from some torque experts
 
Phil, want to see how your torque wrench feels? Set it to 20 in.lb., and hold it in your right hand as shown in the picture. Push against the head with your thumb and you will feel it "release" or "click".
 
no title

I didn't see where anyone answered these, but then again, I didn't read all the replies:

1) For a torque wrench, what's the diff between 1/4" drive, and 3/8" drive (what is the drive?). Which do I want?

the difference is the size of ratchet or torque wrench that fits in your socket.

Torque wrenches that measure inch/pounds are usually 1/4 inch drive.

Torque wrenches that measure foot/pounds are usually 3/8 inch drive or larger. I used a 3/8 drive on the bigger engine mount and wing mount bolts. You won't use one of these big boys very often. Unless you plan to branch out into other mechanical stuff, just borrow one from a pal.

2) How do I get those self-locking nuts off?

You can cut them as someone else has suggested, but then you run the risk of accidentally making a groove or heaven forbid, a hole someplace where you don't want it. I've had a bit of luck just unscrewing them. Sounds silly cuz they're stripped, but it works. Hold the bolt head with a wrench. Grab the nut with a pair if vise grips and gently pull as you unscrew it. It's already stripped, so you can't do any more damage to it, and it's probably not very tight either, so it'll be fairly easy to turn. Be sure that as you turn the vise grips you don't scratch the underlying metal. If that doesn't work you can always revert to a cutting wheel.

Whatever you do, just be really really careful, and don't do anything when you're tired, hot, or frustrated. This project is going to take a long time. With that in mind, there's no need to rush through any step along the way. You'll be happier with the results. As you work on this project over time, you'll find there's more to learn, no matter what your previous experience, so ask lots of questions.

Make friends with your local builders, and consider joining the EAA if you haven't already. I've found that because we share a common interest, most homebuilders and aircraft owners are happy to lend a hand, lend tools, give advice, or even teach a skill.

One other thing. A side benefit to being a home builder is that it's a good excuse to BUY MORE TOOLS

Good luck and blue skies...
 
Ottawa builder

Phil,
I am building a 6A in Ottawa - fuselage in progress - and, while I make no claim to any particular expertise, I have scratched my head over the last number of years about many of the problems/questions that you are may now have and will run into as you get further into the project.
Feel free to contact me, or come and visit my project, and I will provide you with what assistance I can.
You can contact me off list.
Bill Brooks
691 Island Park Drive
Ottawa, ON
K1Y 0B8
(613) 729-4437
[email protected]
 
IowaRV9Dreamer said:
I had read somewhere that you should add the torque required to get the nyloc nuts to turn to the desired torque. This makes sense to me. What I couldn't figure out was what is this "rolling friction"? I couldn't measure it with any tool I own, so I "estimated" and torqed to 28 inch pounds.
Click to expand...

Dave--I checked it once with somebody who had a dial torque wrench and the friction of the nut was about 7# for the AN365 nylocs (more than I expected). I'm sure that it will vary with how hot or cold it is, but everything I've seen posted here on the forum for a friction factor ranges from 6-8#, so 7# is probably right most of the time. Thus, I tend to set my wrench at 29-30# for normal AN3 hardware. I know the best way to determine it would be to probably check it on EVERY nut you torque, but I think ballpark is generally close enough. My A&P and tech advisors kind of laughed at the do-it everytime routine and said to get a ballpark and go with that. On AN4 hardware, the acceptable range is 50-70#, so I just set it up near the upper end of the range which should account for the friction in the AN4 nyloc. Hope this helps.
 
Run-on or drag torque

There is a lot about measuring run-on or drag torque in the following link:

http://www.vansairforce.com/community/showthread.php?t=7904&highlight=torque

I reported measuring specific run-on torques for an application of AN3 and AN4 hardware. These were on my main gear mounts. Of 10 AN4 bolts into anchor nuts and another 2 into 365 nuts, my run-on was 7-20 inch pounds.

On my 14 AN3 bolts, all into 365 nuts, the run-on torque was 7 to 15 inch pounds. This points out the need to measure run-on during all torquing operations. Of note, even the minimum run-on torque WAS GREATER than the delta between the minimum and maximum spec torque of 5 inch pounds for AN3 bolts, (spec torque is 20-25 inch pounds).

Circular: AC43.13-1B

Get the circular,
Read the circular,
Be the circular. :D

Jekyll
 
You didn't hear the click

prkaye said:
So I went ahead and used these parts. I set my torque wrench for 20in-lbs, and began to tighten them. The torque wrench never released (although I've never used a torque wrench so I'm only guessing what this would feel like. What happened was that the nuts eventually got to a point where they turned sort of freely, without tightening on the bolt anymore. This made me wonder...
Phil
Click to expand...

Phil, I had a similar problem. The click didn't arrive (it seemed to me...). I went to my local aero club mechanical and he showed me (in 2 seconds) which was the "click" (see the photo with the wrench in the hand and thumb). Actually, it clicked in my shop, but I thaught it was an instrument tolerance, because I couldn't believe that a so light pressure would be enough. So, I continued since bolt and nut were extratightened (and not safe).
So, I think you went too far with tightnening yours. Remove them (as indicated), throw them away and replace.
Camillo
 
Really guys, 20 in. lb. is nothing! Don't use a torque wrench that starts at 20 in. lb.; it won't be accurate enough. Get a beam type, or if money is no problem, get a Snap-On dial type that is attached to a screwdriver handle so you can read the nylok friction while you're tightening.
http://buy1.snapon.com/catalog/item...1&group_ID=968&store=snapon-store&dir=catalog
Item shown is not the correct range, but is just showing the style.
If you're worried about about overtightening these AN-3 bolts, then use a nut driver and don't overdo it with that, either!
 
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Nuts, torque specs, identification

Gil (az__gila) gives good advice which we find in this thread. Given that our RV9A is our first kit airplane and ideally, we'd like live long enough to build another, we plastered the walls of our shop with various charts & legends (instead of girly photos) so we could identify nuts, bolts, washers and rivets. We also went to the dollar store and bought clear plastic parts bins so we could segregate the nuts, bolts and washers into separate bins. Ditto for rivets. Hard, soft, flush, round tops.

Spend a Saturday on organization. Payback is exponential.

Van's little goody bags frequently come in plastic and have the contents listed on the bag. Sometimes, not always, the contents actually match the label but more often than not, Van's ships using paper bags which have no legend as to the contents. Coupled to the fact that the contents are frequently wrong, the builder needs to assume responsibility and create an organizational system that allows steady progress.

Fortunately, Gil lives nearby and I have a secret key to his hangar. We just wait till he goes to work and then it's....

FREE PARTS!!

Barry
Tucson
 
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