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Posted: 1/4/2005 3:21:06 PM EDT
[Last Edit: 1/4/2005 3:57:04 PM EDT by windom]
I'm assembling an upper, and I got the barrel nut greased, but when I torque it down to hand tight, the hole doesnt line up for the gas tube. I put my torque wrench on, and it reads only about 20ft lbs till the next hole is lined up after hand tight. I go to the next hole after that, but it won't go any farther than in between the two, and my torque wrench reads 65ft lbs so I stopped. I can get it lined up, but it would be like 20-25ft lbs. Any suggestions? I was thinking my torque wrench is inaccurate, it's a craftsman, but it hasn't been used much, only for spark plugs. How tight are these nuts supposed to be? Do you have to bear down on it pretty hard?

Here are some pics. The current "hole" is at 25 ft lbs, or a little less. To get to the next hole on the left, it gets stuck in between the two holes like I said above, and the reading goes over 50. I have plenty of grease, it's not stripped or galled up, and it freely threads on. I would preferably like to have a tighter installation.





Link Posted: 1/4/2005 3:23:14 PM EDT
tag
Link Posted: 1/4/2005 4:01:20 PM EDT
The torque wrench strikes again!!!! I keep telling them, but they never learn.

Here's a tip - watch the barrel nut, not the wrench. Throw away the torque wrench and replace it with a breaker bar so you won't have any meaningless numbers to get all flustered about. And read this thread thoroughly. Then try it again.
Link Posted: 1/4/2005 4:04:02 PM EDT
[Last Edit: 1/4/2005 4:04:17 PM EDT by windom]

Originally Posted By Homo_Erectus:
The torque wrench strikes again!!!! I keep telling them, but they never learn.

Here's a tip - watch the barrel nut, not the wrench. Throw away the torque wrench and replace it with a breaker bar so you won't have any meaningless numbers to get all flustered about. And read this thread thoroughly. Then try it again.



Ah!!! I never found that thread. I found a similar one saying to use a breaker bar, but nothing on not using a GI wrench. I appreciate your help a lot.

FYI this is my first upper I've ever built.
Link Posted: 1/4/2005 4:06:30 PM EDT
I had this exact thing happen on my last build. I went with the tighter than hell option for 1000.

I just didn't like the idea of the nut only being 20 or so lbs so I wrenched her on there. Of course the whole idea is that the thing won't move because of the gas tube being threaded through it but it just didn't seem right in my gut. That could be from wrenching on too many cars or something I don't know but it shoots fine and that's all I care about. I didn't bother with the torque wrench but I am sure it is at the upper threshold of the 80ft lbs limit.

Good luck, if it really bothers you take it to a smith and have them check the headspace for that extra insurance factor. Not that headspace would make a difference how tight it is but it might ease the doubt?

Link Posted: 1/4/2005 4:48:30 PM EDT
you should have stoped at 20 ftlbs.
Link Posted: 1/4/2005 5:38:47 PM EDT

Originally Posted By 556Cliff:
you should have stoped at 20 ftlbs.



No damage to the nut or threads was done. I checked it over up close multiple times, and tightened in an even fashion, no jerking. It's fully assembled now, just waiting for my handguards, and KAC RAS.
Link Posted: 1/4/2005 5:45:58 PM EDT

Originally Posted By bosifus:

Good luck, if it really bothers you take it to a smith and have them check the headspace for that extra insurance factor. Not that headspace would make a difference how tight it is but it might ease the doubt?




Headspace and torqueing the barrel nut are mutually exclusive, of course. Headspace is set at the factory when the barrel extension is mated to the barrel.

Checking never hurt, on the other hand. But I wouldn't pay to have this done. If your rifle is running fine with no strange marks on the cases you are good to go.
Link Posted: 1/4/2005 6:28:40 PM EDT
one thing i learned while using that barrel wrench- pull out your torque wrench, flip around the barrel wrench and then reinsert the torque wrench. basically, you are keeping your moment arm turning on the same plan as the barrel nut. the other way, you are moving the torque wrench farthar from the nut and i've had problems with it all wanting to deflect.
Link Posted: 1/4/2005 6:42:38 PM EDT
every colt upper/barrel I've had, the barrel nut wasn't much tighter than hand tight and the barrel never came loose on me. all the builds I do now, I just hand tighten the nut and then run it up until the gas tube lines up. just guessing-maybe 20 to 30 foot pounds. I haven't used a torque wrench yet and I can still sleep at night.
Link Posted: 1/4/2005 6:59:33 PM EDT
I used Homo_Erectus's method of hand tight then line up the hole with a GI wrench.

70 rounds and she hasn't moved. I really dont expect it to go anywhere. If you work on cars, (i do) look at it this way. The barrel nut is like a castle nut, and the gas tube is like a cotter pin.

I don't think it's going anywhere. but I will check it periodically until I get about 1K rounds through it.
Link Posted: 1/5/2005 8:34:09 AM EDT
I've done several upper lately and it ALWAYS seems that the alignment is just short of a hole just barely hand-tight.

I really had to gorilla one to get it around to the next hole. I don't want to know what the torque value would have been.

My thought: If the barrel nut is not torqued to something greater than finger tight, it will naturally want to loosen (I've had enough nuts and bolts fall off of my motorcycles to know this bit of physics is true). As it loosens, it starts to press against one side of the gas tube (left side looking down the rifle). Over time, that just can't be a good thing, especially using a free-float tube where there's nothing else keeping the forearm upright other than that gas tube in its little tunnel. I would eventually expect FTEs from gas leak or FTF when the key/tube alignment gets too far off.

My 2 cents.

Link Posted: 1/5/2005 10:50:01 AM EDT
If you have trouble reaching the next hole, back off, and tighten several times, and it will work up to the next hole.
Link Posted: 1/5/2005 11:04:05 AM EDT
#1 - you don't mention torquing it 3 times before doing your final
Link Posted: 1/5/2005 12:46:08 PM EDT

Originally Posted By fight4yourrights:
#1 - you don't mention torquing it 3 times before doing your final



Nor moly greasing the contact lip of the upper barrel socket, and the inside upper lip contacting edge of the barrel nut.
Link Posted: 1/5/2005 12:58:49 PM EDT

Originally Posted By A_Free_Man:
If you have trouble reaching the next hole, back off, and tighten several times, and it will work up to the next hole.




If you tighten a barrel nut, then loosen it and retighten it and the nut travels further than it did before, that is a prime indication that you are stretching the aluminum and damaging the upper receiver. And deliberately damaging your upper receiver is a really bad idea.

I don't know who started this horrendously stupid "tighten and loosen multiple times" procedure, but I'd like to smack him upside the head with his torque wrench while he tries to watch the scale and determine how many ft-lbs. I'm applying to his noggin. Three times.

When installing a barrel, you should tighten the barrel nut exactly once, then stop.
Link Posted: 1/5/2005 1:02:20 PM EDT
Get that wrench calibrated. This place is awesome and not very expensive. They are ISO compliant and A2LA certified. I send my wrenches there once a year to make sure they are accurate. They will even adjust them for you and provide a report of the readings.

National Calibration and Testing Labs
Link Posted: 1/5/2005 3:48:08 PM EDT

Originally Posted By Homo_Erectus:
I don't know who started this horrendously stupid "tighten and loosen multiple times" procedure, .



It was by a staff that had their Doctorates in Engineering, Physic, and Metallurgy.
Link Posted: 1/5/2005 3:55:51 PM EDT
You're supposed to use a torque wrench when installing barrels????
Link Posted: 1/5/2005 5:14:43 PM EDT

Originally Posted By Homo_Erectus:

Originally Posted By A_Free_Man:
If you have trouble reaching the next hole, back off, and tighten several times, and it will work up to the next hole.




If you tighten a barrel nut, then loosen it and retighten it and the nut travels further than it did before, that is a prime indication that you are stretching the aluminum and damaging the upper receiver. And deliberately damaging your upper receiver is a really bad idea.

I don't know who started this horrendously stupid "tighten and loosen multiple times" procedure, but I'd like to smack him upside the head with his torque wrench while he tries to watch the scale and determine how many ft-lbs. I'm applying to his noggin. Three times.

When installing a barrel, you should tighten the barrel nut exactly once, then stop.




Ever read the Army Manual?
Link Posted: 1/5/2005 6:02:37 PM EDT
I have the US Marine Corps Manual right here and it specifically states to tighen and then losen 3 times and then on the third time to torque to 31-35 foot lbs with both wrenchs together. It also does not give a maximum torque value of 80 foot lbs.

Corbett
Link Posted: 1/5/2005 6:11:35 PM EDT

Originally Posted By Irunwire:
I have the US Marine Corps Manual right here and it specifically states to tighen and then losen 3 times and then on the third time to torque to 31-35 foot lbs with both wrenchs together. It also does not give a maximum torque value of 80 foot lbs.

Corbett



80 ft lbs is a lot of force. Is there any manual stating this in a pdf or online somewhere that I can see?
Link Posted: 1/5/2005 6:25:02 PM EDT
Windom,

As long as the shoulder on the barrel extension is flush and snug against the upper, and the barrel nut is tightened to the first available notch that requires some force on the wrench to reach then you are done.

This taint rocket science. Listen to homo E , he knows what he is talking about.
Link Posted: 1/5/2005 6:32:02 PM EDT
[Last Edit: 1/5/2005 6:34:15 PM EDT by Homo_Erectus]

Originally Posted By Dano523:

It was by a staff that had their Doctorates in Engineering, Physic, and Metallurgy.



And who would that be? I mean, you since you know the exact advanced degrees these people have, you won't have any problems telling us their names. I sure no one here would just pull a statement like that out of thin air with absolutely no info to back it up, now would they....



Originally Posted By fight4yourrights:

Ever read the Army Manual?




Yes I have, and that's the problem. People get so hung up on a meaningless torque value that they screw up an operation that consists of merely tightening one single nut. Check out this thread for a recent example.

Keep in mind that military TMs are written for draftees with a wide range of IQs and skills sets. That's why the Army also issues manuals that cover topics like how to march, eat, lace your boots, and use the latrine. My method assumes that you have at least average intelligence and some common sense, and it has worked well for dozens of ARF.comers. But if you feel the need to read a book in order to correctly walk, tie your shoes or wipe your ass, then by all means you should be following the procedures in the Army manuals.
Link Posted: 1/5/2005 6:51:05 PM EDT

Originally Posted By Homo_Erectus:



If you tighten a barrel nut, then loosen it and retighten it and the nut travels further than it did before, that is a prime indication that you are stretching the aluminum and damaging the upper receiver.
...................

When installing a barrel, you should tighten the barrel nut exactly once, then stop.




I disagree. What you are doing when tightening the nut 3 or more times is flatening the burrs, lint, parkerizing, etc that is needed to get a proper fit. It's not like if you snug it up 50 times it goes farther each time. Tighten/snug the nut up a few times until it quits turning farther than before. You now have acheived a proper mating surface between the nut and the barrel extension. Then tighten the nut to the next notch while using a breaker bar or ratchet (not a torque wrench).
Link Posted: 1/6/2005 2:12:37 PM EDT
[Last Edit: 1/6/2005 2:14:58 PM EDT by Irunwire]
Homo_Erectus

[Keep in mind that military TMs are written for draftees with a wide range of IQs and skills sets. That's why the Army also issues manuals that cover topics like how to march, eat, lace your boots, and use the latrine. My method assumes that you have at least average intelligence and some common sense, and it has worked well for dozens of ARF.comers. But if you feel the need to read a book in order to correctly walk, tie your shoes or wipe your ass, then by all means you should be following the procedures in the Army manuals]

Well, I am in the Air National Guard working full time on F-16s after serving six years in the Air Force working on KC-135s and if you do not use manuals to do your job planes will crash and peolpe may die. As for Draftees, we have not had those since the very early 70's. I surely do not remember any manuals telling me how to do any of those other things, but manuals like that are used to teach enlistees order and disipline. And finally us military members use those manuals to defend our and your freedoms so we can have places like this to talk about our hobbies.

God Bless the USA
Link Posted: 1/6/2005 6:17:02 PM EDT

Originally Posted By Irunwire:

Well, I am in the Air National Guard working full time on F-16s after serving six years in the Air Force working on KC-135s and if you do not use manuals to do your job planes will crash and peolpe may die. As for Draftees, we have not had those since the very early 70's. I surely do not remember any manuals telling me how to do any of those other things, but manuals like that are used to teach enlistees order and disipline. And finally us military members use those manuals to defend our and your freedoms so we can have places like this to talk about our hobbies.

God Bless the USA




Nobody is talking about repairing jet aircraft. Comparing F16 maintenance with an AR barrel change is like equating nuclear power plant operations with screwing in a light bulb. Obviously years of religious indoctrination has destroyed your ability for logic and critical thought.

It's too bad, because if anyone would understand the mechanics behind screwing down one single nut, you should. I've never worked on a jet, but the last time I did a valve job on my truck, I torqued down the head bolts exactly once with no multiple tightening and loosening. In fact, on my friend's Ford truck, his head bolts can only be torqued down one time and cannot be reused. If the head bolts become loose, you have to replace them.

My point is - yes, there are specific reasons the TMs use such complicated and deliberate procedures. It's because they have to write instructions for someone who may have very little education, no experience, and has maybe never even seen an M16 rifle before in their lives. These procedures can also be taught in a cookbook manner by rote memorization. You can't write in an army manual "hand tight and to the next notch" because you'd get everything from 4 turns loose to tightening using a 6 ft. extension on a breaker bar and having the entire platoon lean on it.

Basically there's only one notch an a barrel nut that is going to line up within the normal torque range. And it really bothers me to see people here try over and over, again and again to merely tighten one single nut, but they're so hung up on a meaningless torque number that they fail repeatedly at tightening one single nut, and instead damage upper receivers, barrel nuts, their nerves, and their knuckles.

I'll say it again - mounting a barrel on an AR is a 10 minute job. If it takes you longer than that, you're doing something wrong. And it probably involves a torque wrench.
Link Posted: 1/7/2005 7:45:27 AM EDT

Originally Posted By windom:
I put my torque wrench on, and it reads only about 20ft lbs till the next hole is lined up after hand tight. I go to the next hole after that, but it won't go any farther than in between the two, and my torque wrench reads 65ft lbs so I stopped. I can get it lined up, but it would be like 20-25ft lbs. Any suggestions? I was thinking my torque wrench is inaccurate, it's a craftsman, but it hasn't been used much, only for spark plugs. How tight are these nuts supposed to be? Do you have to bear down on it pretty hard?




One more thing that I forgot to mention. The torque values listed in the TM are for use WITH the barrel wrench. When you are using a barrel wrench and torque wrench together, the actual ft. lbs. on the barrel nut are greater because the torque wrench is offset from the center of the barrel nut. You are essentially using the barrel nut wrench as leverage. 30 ft. lbs. sounds too light to you, but the force on the barrel nut is actually greater, and also no more than if you use the simple no torque wrench method.
Link Posted: 1/7/2005 8:45:14 AM EDT
????

The torque wrench is measuring the torque. It measures it at the head of the wrench. Torque is Torque. The only thing that changes when you use a longer torque wrench, an extension or pry bar is the amount of force you have to use to get 30lb.ft. of torque on the nut.

The OFFSET you mention doesn't change anything unless the torque wrench bends and does not stay in the same place relative to the barrel wrench.

Take a look- the barrel wrench has the 1/2" wrench opening for a 1/2" wrench. if the "offset" made a difference, they would have added it in. Who in the hell would be tightening the nut with the wrench by hand? tightening the nut by hand is the first step. lining up the holes for the gas tube requires a tool, the tool being the barrel nut wrench AND a torque wrench, etc. most people have access to 1/2" drive wrenches. would you have rather paid twice as much money for the barrel nut wrench just because it's wrench was attached? the 1/2" socket wrench is not used as a ratcheting socket wrench. it is simply an extention of the wrench. they figure you'd have your own extension, so why use more metal and do more machining to make a friggin' barrel nut wrench? i'm glad my barrel nut wrench does not include a large arm. it fits in my ar toolkit. when i need to use it, i grab the tool you are supposed to use.
Link Posted: 1/7/2005 9:07:59 AM EDT

Originally Posted By JosephR:
????

The torque wrench is measuring the torque. It measures it at the head of the wrench.



Correct. And the head of the wrench is being offset from the barrel nut by the barrel nut wrench. It does have an impact on the reading. The training manual does "add it in." It is very specific that the minimum torque value listed is to be obtained using a torque wrench and barrel wrench together.

As for the rest of that raving... . I am lazy and don't feel like addressing it.

Well, OK a little bit. The original thread starter thought that 20-25 ft lbs. was too light when using his barrel wrench and torque wrench together. I was simply pointing out that there is more force being applied to the barrel nut than 25 ft lbs. You obviously did not comprehend this.
Link Posted: 1/7/2005 10:04:01 AM EDT
[Last Edit: 1/7/2005 9:55:14 PM EDT by 1Gunner]
Barrels have nuts?

ETA: Because I have added serious posts below here I want to emphasize this was a joke.
Link Posted: 1/7/2005 10:41:05 AM EDT
are you talking about the wrench moving farther from the center of the moment arm or are you referring to the fact that depending on which side you place the wrench, the wrench can be forward of the nut?

It's only raving because I didn't go about it very clearly. I started typing and then thought of examples while i was typing. unfortunately i am too lazy to stop, make a professional looking outline, then copy and paste.

if the ratchet wrench or torque wrench is placed into the 1/2" square on the 3-pronged barrel nut wrench so that they form a straight line from the bore to the tip of the handle, then 30 pounds of torque at the barrel is 30 pounds of torque at the tip of the handle- it just takes less human force if you are trying to create 30 lbft closer to the barrel.

I don't care what the original conversation was. I'm correcting you, not anything else.
Link Posted: 1/7/2005 11:06:12 AM EDT
[Last Edit: 1/7/2005 1:46:05 PM EDT by Halfcocked]
JosephR, You're wrong.

Torque is in Length Pounds. 35 Foot pounds of torque could be 1 pound of force at 35 feet or 35 pounds of force at 1 foot and everything in between that multiplies out to 35. Adding an increment of length with the same force, increases torque. Think lever and fulcrum.

Homo, You're right.

The stress is at the barrel extension and barrel. The lower dosen't do much in this regard except hold the barrel in alignment with the bolt/bolt carier, and hold it to the lower.
Link Posted: 1/7/2005 12:46:22 PM EDT
THAT'S EXACTLY WHAT I'M SAYING TO YOU- THAT IT DOESN'T MATTER IF THERE IS A RATCHET, AN EXTENSION, OR ANYTHING ELSE SIMILAR- 35 FOOT-POUNDS ARE 35 FOOT POUNDS.

you said:

---------------------------------
One more thing that I forgot to mention. The torque values listed in the TM are for use WITH the barrel wrench. When you are using a barrel wrench and torque wrench together, the actual ft. lbs. on the barrel nut are greater because the torque wrench is offset from the center of the barrel nut. You are essentially using the barrel nut wrench as leverage.
---------------------------------

that portion in red shows that you think that with an extension, torque changes.

that portion in blue shows that you don't realize that the two wrenches together are one lever and work together and don't change the amount of torque- they change how much energy YOU have to put into the lever to turn it.

again, if you think that something attached to the barrel nut wrench means that torque changes because the end of the extension is not at the center of the bore. you are trying to say that the amount of torque between the two wrenches increases and that is true- there is a lot ot torque created between the 1/2" ratched drive and the square hole in the barrel nut. But, the teeth in that ratchet can take more than 35 lb-ft of torque, so the barrel nut turns before any values in torque change at the connection point between the two wrenches.
Link Posted: 1/7/2005 1:18:37 PM EDT
[Last Edit: 1/7/2005 1:32:13 PM EDT by laynlow40]
Oh for fuck's sake.

You just don't get what I am telling the original poster, or the mechanics of what is going on.

If I want to torque a barrel nut to a true 35 ft lbs, setting a torque wrench on 35 ft lbs and using it in combination with a barrel wrench WILL NOT TORQUE THE BARREL NUT TO A TRUE 35 FT LBS. THE BARREL NUT WILL HAVE BEEN TIGHTENED MORE THAN 35 FT LBS.

The damn torque wrench is measuring force at it's end. If I move the wrench out at any point away from the center of the barrel nut on the lever I am using to tighten the barrel nut with I will have exerted 35 ft lbs of force on the lever AT THAT POINT, but not on the barrel nut!

OK, ETA an example:

If I am using a wrench that is 12" long (here is the foot in foot pounds) to tighten lug nuts on a truck, and I want to exert 200 pound feet of torque on the lug nut, then I must exert 200 ft. lbs of force on the end of the wrench. Now if I use a wrench that is 24" long, I only need to exert 100 lbs of force on the end of the wrench to achieve the same 200 lb feet of torque on the nut.
Link Posted: 1/7/2005 1:33:08 PM EDT
Hey- i'll pretend you are right and that I am just misunderstanding you. What happens if he goes over 35 lbs?? complete and utter destruction?

the army manuals say 31-80 only because it will take at least 30 to get it hand tight and for a hole to almost line up. you'd have to get up to 35 to actually get the hole to line up. if, for some reason, you were just a tiny tiny bit PAST being ligned up, it would take up to and no more than 80 lbs.

the numbers came when they decided that they needed to include numbers in an armorer's manual. you can pretty much bet that if you were to tighten one by hand, you could almost get the holes aligned, but you would still need a wrench. at that point, there would have to be 35 or so to get it to move that last bit. you can be absolutely certain that no barrel nut CAN be tightened past, but near, 80 AND have holes line up.
Link Posted: 1/7/2005 1:40:53 PM EDT
[Last Edit: 1/7/2005 1:41:16 PM EDT by Halfcocked]

Originally Posted By JosephR:
Hey- i'll pretend you are right and that I am just misunderstanding you. What happens if he goes over 35 lbs?? ...



That's not the point.

Were talking about your understanding of torque.
Link Posted: 1/7/2005 1:50:13 PM EDT
At no time have I been arguing the correct amount of force to apply to a barrel nut. Never. Didn't happen. OK?

I don't use a torque wrench to install a barrel. I get the nut hand tight and use the barrel wrench to tighten to the next available slot just as HE has described ad nauseum (not his fault he had to BTW).

WINDOM THOUGHT THAT 20-25 FT LBS WAS TOO LIGHT FOR A PROPER INSTALL. ALL I WAS DOING IS TELLING HIM THAT EVEN THOUGH HIS TORQUE WRENCH READS 20-25 FT LBS THE ACTUAL FORCE EXERTED ON THE BARREL NUT IS GREATER! THAT IS IT. NOTHING MORE. DON'T READ WHAT YOU WANT INTO IT.
Link Posted: 1/7/2005 6:02:32 PM EDT
where did you learn torque? automotive school? I learned mine a little differently.
Link Posted: 1/7/2005 6:17:16 PM EDT
[Last Edit: 1/7/2005 7:15:26 PM EDT by Halfcocked]

where did you learn torque? automotive school? I learned mine a little differently.



Comic books and bubble gum wrappers.
Link Posted: 1/7/2005 6:18:04 PM EDT
[Last Edit: 1/7/2005 6:19:34 PM EDT by Irunwire]
You are almost exactly right Homo, working on F-16s does not compare to working on barrels. It takes a lot more critical thinking to make an airplane fly that has thousands of parts compared to hundred or so in an internal combustion engine. I also used to be a ASE certified mechanic before and while in the Air Force. Now in 99 percent of the shop manuals for installing heads on a block, to include one time use head bolts, it is highly recommend to step torque your bolts, usually in 3 increments. Now, i am not bashing you by any means and I completely understand your thinking, to each there own, but by following some kind of manual you are better off. By tightening three time you are ensuring that you are completely seating the barrel into the barrel extension. So if you choose to hand tighten the barrel and then advance to the next alignment slot, I would be willing to say that you are well with in torque limits. By adding any extension to any wrench your are adding more leverage thus torque will be increase.

Link Posted: 1/7/2005 6:48:54 PM EDT

Originally Posted By Irunwire:
By adding any extension to any wrench your are adding more leverage thus torque will be increase.




Yup.
Link Posted: 1/7/2005 8:52:56 PM EDT
[Last Edit: 1/7/2005 9:56:25 PM EDT by 1Gunner]

Originally Posted By laynlow40:
Oh for fuck's sake.

You just don't get what I am telling the original poster, or the mechanics of what is going on.

If I want to torque a barrel nut to a true 35 ft lbs, setting a torque wrench on 35 ft lbs and using it in combination with a barrel wrench WILL NOT TORQUE THE BARREL NUT TO A TRUE 35 FT LBS. THE BARREL NUT WILL HAVE BEEN TIGHTENED MORE THAN 35 FT LBS.

The damn torque wrench is measuring force at it's end. If I move the wrench out at any point away from the center of the barrel nut on the lever I am using to tighten the barrel nut with I will have exerted 35 ft lbs of force on the lever AT THAT POINT, but not on the barrel nut!

OK, ETA an example:

If I am using a wrench that is 12" long (here is the foot in foot pounds) to tighten lug nuts on a truck, and I want to exert 200 pound feet of torque on the lug nut, then I must exert 200 ft. lbs of force on the end of the wrench. Now if I use a wrench that is 24" long, I only need to exert 100 lbs of force on the end of the wrench to achieve the same 200 lb feet of torque on the nut.



Fundamentally wrong, suggest taking an engineering statics course.
Link Posted: 1/7/2005 9:20:32 PM EDT
[Last Edit: 1/7/2005 9:23:41 PM EDT by 1Gunner]
A torque wrench with a setting of 35 ft-lbs will transfer 35 ft-lbs to the barrel nut no matter then length of the barrel nut wrench it is attached to.

There is a fundamental difference between adding a wrench, which converts a force into a moment at the end where the (sometimes ratcheting) direction switchs to a different and 90 degree angle and adding a straight bar such as a simple metal tube over the barrel wrench.

Most of everyone's post with respect to a torque wrench is wrong and is why shit breaks and kills people.

Please understand this difference between a wrench that is bent at the end, and a wrench that is completely straight. If it is completely straight, then yes, the moment about the barrel wrench will be the distance from the center of the barrel nut times the force at the end of the straight bar. But if it is a bent (there is probably a better word than bent) wrench like a torque wrench or regular ratcheting wrench, then the torque at the end of the wrench transfers is the torque at the end of any extension.

A difficult concept granted, but this needs to be cleared up.

Link Posted: 1/7/2005 9:25:22 PM EDT
[Last Edit: 1/7/2005 10:01:49 PM EDT by 1Gunner]

Originally Posted By Halfcocked:

Originally Posted By Irunwire:
By adding any extension to any wrench your are adding more leverage thus torque will be increase.




Yup.



This depends on if the extension to any wrench is also a wrench or just a straight bar!!!!!!

Two wrenches is not the same as one wrench with a straight extension!!!!

A wrench transfers torque only and no additional leverage!!!!!

FWIW: I am a semester away from a masters of mechanical engineering

flame away, I'm right on this one
Link Posted: 1/8/2005 8:19:27 AM EDT
If the nut lines up at 35 ft-lb it is a miracle. It may line up at 25, or 70. Where it lines up, it lines up.
Link Posted: 1/8/2005 8:25:13 AM EDT
[Last Edit: 1/8/2005 3:32:17 PM EDT by 556Cliff]

Originally Posted By Homo_Erectus:

If you tighten a barrel nut, then loosen it and retighten it and the nut travels further than it did before, that is a prime indication that you are stretching the aluminum and damaging the upper receiver. And deliberately damaging your upper receiver is a really bad idea.



My upper receiver isn't destroyed just because I went to 31 ft-lbs with a torque wrench a few times is it?

How do I know if the threads are ruined or not? There are a few flakes of finish that came off of the outer edge of the threads, but that doesn't mean that it's ruined does it? Other than that, the threads look pretty good.

Should I start over again and buy another receiver?

I have another upper receiver that I had to go somewhere around, I'm guessing 70 ft-lbs to get the next gas tube notch lined up and it has some pretty bad galling on it's threads. Is this receiver destroyed?

Also will the Homo_Erectus barreling method work with once barreld with a torque wrench upper receivers?
Link Posted: 1/8/2005 9:13:46 AM EDT
I am not talking about the length of the barrel wrench being the determining factor. I am talking about the point on the barrel wrench where we attach a torque wrench being the determining factor. Who would have thought this would be hard to understand?

I am tired of trying to explain it though, so whatever.
Link Posted: 1/8/2005 9:23:00 AM EDT
[Last Edit: 1/8/2005 9:29:16 AM EDT by 1Gunner]
There are no determining factors here besides the setting of the torque wrench. A wrench is different from a straight bar used as an extension.

Two wrenches act as a mechanism with two links transferring a moment, not any forces (other than the equal upward force carried by the upper receiver holding block in the vise). If you have a straight bar attached to the barrel wrench than you would be right, but adding another wrench such as a torque wrench would add no new leverage.

ETA: It is hard to understand the complete physics of the problem, but there is indeed a complete difference between two wrenches used together and a wrench with a straight extension. Make a free body diagram of just the barrel wrench, and then add a moment at the end (from a wrench) or force (from a straight extension) and sum the moments about the nut center and you will see. You can't consider the barrel wrench and additional torque wrench to be one body.
Link Posted: 1/8/2005 9:34:20 AM EDT
Sigh.

Link Posted: 1/8/2005 9:51:27 AM EDT
Ok, to redirect back to square 1:

1. Due to the design of the Stoner Gas system the Bolt Locks into the Barrel Extension.

2. As long as the barrel extension is in correct relation to the barrel, accuracy will not be affected. The only effect could be that relation between the sights and the barrel could drift.

3. Even if you went 1 notch too loose, the nut would not and could not unscrew due to the gas tube locking it in place.

4. If you did leave it that loose and the nut backed off, the worst thing that could happen is that the key contacts the gas tube and causes a Failure to Feed.

5. Unless you are in a life or death situation, this will result in you pulling the gas tube and tightening the nut.

6. If you are carrying your rifle in a life or death situation, then you should be doing regular PM's and Inspections on it, and would notice any issues before they caused a malfunction.

As we can see, there are several ways to skin a cat, and more ways to tighten a nut.

I am a LEO, my life depends on my rifle. I have carried M16's worked on my Marine Armorers for most of my adult life. I am using Homo_Erectus's method because it makes sense. There is no reason to put undue stress on a aluminum part. I know from experience what 26-30 ft. lbs. feels like. I can tell you that after hand tight and lining up the notch, that sucker is a little over 30. I don't really care to throw my wrench on it and check.

The argument about torque mesurement is assinine. Look at your manual for your wrench. It tells you to only holt the wrench at the grip when torqueing. The reason is because of leverage. If you change the lenght of the lever, you change the torque being applied. I am ASSUMING that the TM takes into account the distance from the axis of the bore to the 1/2" attachment on the GI Wrench. My DPMS wrench looks to have the hole the same distance, and I would hope others would as well.

I really don't see where this can go from here. Do it however it makes you feel comfortable. It's your rifle next to your face.

I have been around TM's long enough to know that Homo_Erectus is right, the TM dosent always show the best way to do something. It's just the easiest way to clearly describe it.
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