ar barrel torque
- Thread starter bcarver
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FrankenMauser
New member
Actual torque with greased threads (to prevent galling) is 30-80 lb-ft for standard barrel nuts and some non-standard nuts (like the Young Manufacturing free-float nuts).
I use moly grease, but pretty much any general purpose automotive grease will do.
If using an adapter longer than approx 2.75" (center of drive hole to center of spanner hole), you need to calculate the torque wrench setting needed to achieve proper torque. This link shows how to do that: Torque Wrench extensions.
(I use the Tapco wrench, inline with the torque wrench. With my torque wrench, the torque settings are 23-62 lb-ft to achieve 30-80 lb-ft actual torque.)
Torque the nut to 30 lb-ft.
Break it loose and back it off at least 1/2 turn.
Torque to 30 again.
Break it loose and back it off at least 1/2 turn.
Torque to 30, and check for gas tube alignment. Increase torque until the holes are aligned, or a maximum of 80 lb-ft is reached.
To get the holes aligned, what I like to do is slowly increase the setting 10-15 lb-ft at a time, so as not to over-shoot the alignment.
If it can't be aligned between 30 and 80 lb-ft, something is wrong. Inspect the barrel, barrel extension, receiver and threads, delta ring (if applicable), and try a different barrel nut.
If you accidentally over-shoot, break torque and back the nut off 1/2 turn. Then retorque to achieve proper alignment. (Don't just turn it backwards until the holes align.)
The Army and Air Force suggested "if not aligned, continued tightening nut until aligned" for the A2s. But any other source limits maximum torque to 80/85 lb-ft (or less).
I use moly grease, but pretty much any general purpose automotive grease will do.
If using an adapter longer than approx 2.75" (center of drive hole to center of spanner hole), you need to calculate the torque wrench setting needed to achieve proper torque. This link shows how to do that: Torque Wrench extensions.
(I use the Tapco wrench, inline with the torque wrench. With my torque wrench, the torque settings are 23-62 lb-ft to achieve 30-80 lb-ft actual torque.)
Torque the nut to 30 lb-ft.
Break it loose and back it off at least 1/2 turn.
Torque to 30 again.
Break it loose and back it off at least 1/2 turn.
Torque to 30, and check for gas tube alignment. Increase torque until the holes are aligned, or a maximum of 80 lb-ft is reached.
To get the holes aligned, what I like to do is slowly increase the setting 10-15 lb-ft at a time, so as not to over-shoot the alignment.
If it can't be aligned between 30 and 80 lb-ft, something is wrong. Inspect the barrel, barrel extension, receiver and threads, delta ring (if applicable), and try a different barrel nut.
If you accidentally over-shoot, break torque and back the nut off 1/2 turn. Then retorque to achieve proper alignment. (Don't just turn it backwards until the holes align.)
The Army and Air Force suggested "if not aligned, continued tightening nut until aligned" for the A2s. But any other source limits maximum torque to 80/85 lb-ft (or less).
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I generally agree with everything FrankenMauser said. But I am going to respectfully disagree with him on one point. The Colt and Military torque specs I have see take into account the use of a specific tool, and using it in an extended position. So it also acts as an extension.
The tool is effectively 2.0" of extension (if I remember correctly) or very close to that amount. That's measured from the center of the torque wrench pivot to the center of the barrel nut.
The bottom line is your torque wrench should be 30-80 ft-lbs when using a 2" extension.
Joe Mamma
The tool is effectively 2.0" of extension (if I remember correctly) or very close to that amount. That's measured from the center of the torque wrench pivot to the center of the barrel nut.
The bottom line is your torque wrench should be 30-80 ft-lbs when using a 2" extension.
Joe Mamma
FrankenMauser
New member
You're correct, I should have been more specific in my post.
But, unless you have a torque wrench with an integral AR barrel nut spanner (I don't know of any), it is assumed that a standard adapter/extension is being used.
I edited my post for a little clarity.
But, unless you have a torque wrench with an integral AR barrel nut spanner (I don't know of any), it is assumed that a standard adapter/extension is being used.
I edited my post for a little clarity.
Dixie Gunsmithing
Moderator Emeritus
Actually, torque it is relative to any length, as long as it calculates to 30 Ft. Lb, or 80 Ft. Lb max to get to the notch.
30 Ft. Lb. (360 inch pounds torque) is a 30 pound weight that is generating torque from 12" (360/12) away from the center line of the barrel, or it can be 15 pounds at 24". At two inches from the barrels center line, it would take 180 pounds force down to get the same torque. Any fastener, nut, bolt, etc, the torque is measured from its center to some arbitrary point where the weight is attached and acts. An inch pound, means a 1 pound force, one inch away from the center, and a foot pound, is 1 pound force at 12 inches away. On a wrench, it is calculated from the middle of the nut, in this case the center line of the barrel, to the middle of the hand grip of the wrench.
If you had a nut adapter for a 12" torque wrench, that had the square hole for the torque wrench two inches from the barrels center, then you would have to take two inches from the wrenches grip length, or cut the weight back accordingly. 360 in lb. divided by 14 inches (middle of that grip) is 25.71 pounds torque.
30 Ft. Lb. (360 inch pounds torque) is a 30 pound weight that is generating torque from 12" (360/12) away from the center line of the barrel, or it can be 15 pounds at 24". At two inches from the barrels center line, it would take 180 pounds force down to get the same torque. Any fastener, nut, bolt, etc, the torque is measured from its center to some arbitrary point where the weight is attached and acts. An inch pound, means a 1 pound force, one inch away from the center, and a foot pound, is 1 pound force at 12 inches away. On a wrench, it is calculated from the middle of the nut, in this case the center line of the barrel, to the middle of the hand grip of the wrench.
If you had a nut adapter for a 12" torque wrench, that had the square hole for the torque wrench two inches from the barrels center, then you would have to take two inches from the wrenches grip length, or cut the weight back accordingly. 360 in lb. divided by 14 inches (middle of that grip) is 25.71 pounds torque.
I think you are missing what we are saying.
For example, the Colt factory procedure for this would have you set your torque wrench to 30 ft-lbs and tighten the barrel nut *with the tool/adapter attached to the torque wrench in the extended position.* This tool/adapter adds 2" of length to the torque wrench, and this is already accounted for in the Colt procedure. The procedure details like lubricating the threads, tightening, retightening, and final tightening are in FrankenMauser's post above.
If you use an different tool/adapter which is shorter or longer than the official tool/adapter, you have to use a different torque setting on your wrench, because the effective length of your wrench is different.
Joe Mamma
Dixie Gunsmithing
Moderator Emeritus
Joe,
No, I see what they're saying, but 30 foot pounds of torque was called out, so no matter what tool you have, you can't get 30 foot pounds torque from a wrench that is longer than a foot from the center of the barrel to the place where the 30 Lb. weight is added on the wrench. If the wrench is longer, over 12" to the center, then you have to deduct that in order for it to be the same torque as what it would at 12 inches. Really, its easier to understand if one converts it to inch pounds.
30 Lb. x 12" = 360 in. Lb.
360/12" = 30 Ft. Lbs or just 30 pounds of weight hanging 12" out.
360/14" = 25.7 Ft. Lbs., but it is the same torque or force applied to the threads as 30 Lbs. from a 12" wrench.
If you were to add 30 pounds at the end of a 14" wrench, the torque would be 420 in. Lb., or 35 Ft. Lb., which is 5 pounds over.
So, if you add a nut adapter to a torque wrench, and it adds two inches of length onto it, to get the same torque force on the threads, as you would have at 12" in Ft. Lbs., you have to deduct over it, and weight the wrench at 25.7 to 26 pounds. Then, when the weight is applied, the threads see the same torque as 30 Ft. Lb.
If it were meant to have 35 Ft. Lb., they would have called that out. Once the term foot is applied, you have to use 12" to calculate it.
No, I see what they're saying, but 30 foot pounds of torque was called out, so no matter what tool you have, you can't get 30 foot pounds torque from a wrench that is longer than a foot from the center of the barrel to the place where the 30 Lb. weight is added on the wrench. If the wrench is longer, over 12" to the center, then you have to deduct that in order for it to be the same torque as what it would at 12 inches. Really, its easier to understand if one converts it to inch pounds.
30 Lb. x 12" = 360 in. Lb.
360/12" = 30 Ft. Lbs or just 30 pounds of weight hanging 12" out.
360/14" = 25.7 Ft. Lbs., but it is the same torque or force applied to the threads as 30 Lbs. from a 12" wrench.
If you were to add 30 pounds at the end of a 14" wrench, the torque would be 420 in. Lb., or 35 Ft. Lb., which is 5 pounds over.
So, if you add a nut adapter to a torque wrench, and it adds two inches of length onto it, to get the same torque force on the threads, as you would have at 12" in Ft. Lbs., you have to deduct over it, and weight the wrench at 25.7 to 26 pounds. Then, when the weight is applied, the threads see the same torque as 30 Ft. Lb.
If it were meant to have 35 Ft. Lb., they would have called that out. Once the term foot is applied, you have to use 12" to calculate it.
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FrankenMauser
New member
I worked with too many ridiculous inch-pound figures in the military. (Like 7,692 in-lb for some of our swashplate bolts. It's 641 ft-lbs. Just call it what it is...)
I prefer to stick with foot-pounds, when the situation is simple enough to allow it.
I prefer to stick with foot-pounds, when the situation is simple enough to allow it.
OK, maybe you and I are going to just have to agree to disagree.
See the picture in this attached document. The tool/adapter that is being used adds 2.0" of effective length (I measured mine to confirm) when it is extended (in-line) like is shown, and that is factored into their recommended torque specs. It even says "Torque is measured when both wrenches are used together."
The Colt factory Armorer's Manual has a different picture. But it shows the exact same tool in the exact same extended position. Colt says the same thing about measuring torque with both tools (oriented the same way)--starting with the same 30 ft-lbs of torque measured by the torque wrench with that 2.0" extension.
Joe Mamma
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Dixie Gunsmithing
Moderator Emeritus
What they are actually doing is telling you to set the wrench at 30 Ft. Pounds, and apply pressure, (and that is if you keep the wrench straight), with the adapter, but what you really have applied to the threads is 35 Ft. Lb. That's what I'm wanting to impress on the readers, is that in actuality, it's not 30 Ft. Lb. torque they are applying to the threads but more.
To be honest, the 30 pounds +/- isn't real critical for what they are doing, seating the threads, but the 80 Ft. Lb. does, as it is a limit, but if you use a different way of tightening the nut, (by shortening the wrench to 12" or just want to know the true torque), what they tell you there is thrown out the window, as then you would have to measure it, and calculate it. At 14" out (adding two inches from the adapter), and setting a wrench at 80 Ft. Lb., you are really applying is 93.33 Ft. Lb. to the thread, maximum.
If you have a different setup or tool to use, as a lot of gunsmiths do, then what they want to know is how much true thread torque they can apply, to get to that notch without going over. If they took what Colt, etc. says for gospel for any setup, and couldn't reach the notch, they may have been able to, if they would have twisted it on up to 93 Ft. Lb., as long as it is a true calculated reading.
To be honest, the 30 pounds +/- isn't real critical for what they are doing, seating the threads, but the 80 Ft. Lb. does, as it is a limit, but if you use a different way of tightening the nut, (by shortening the wrench to 12" or just want to know the true torque), what they tell you there is thrown out the window, as then you would have to measure it, and calculate it. At 14" out (adding two inches from the adapter), and setting a wrench at 80 Ft. Lb., you are really applying is 93.33 Ft. Lb. to the thread, maximum.
If you have a different setup or tool to use, as a lot of gunsmiths do, then what they want to know is how much true thread torque they can apply, to get to that notch without going over. If they took what Colt, etc. says for gospel for any setup, and couldn't reach the notch, they may have been able to, if they would have twisted it on up to 93 Ft. Lb., as long as it is a true calculated reading.
FrankenMauser
New member
I agree that low torque figures here are not highly critical, and that the maximum torque is the critical one.
However, the amount of torque being applied to the threads with the standard 2" barrel nut wrench depends on the length of the torque wrench being used. The longer the wrench, the closer the actual torque will be to the setting on the wrench (assuming it's properly calibrated).
The Army and Air Force standard is a Snap-On brand wrench (or suitable substitute) with a 14.5" pivot-to-grip length (center to center).
With that wrench, a 30 ft-lb setting results in 34.1 ft-lb on the nut.
But, if you have an 18" torque wrench, the nut gets 33.33 ft-lb.
Only if you use a 12" torque wrench, will the nut get 35 ft-lb.
Dixie, I don't think you're using the correct formula to calculate your torque values (otherwise, for instance, your 93.33 ft-lb example should be over 94 ft-lb). It isn't a matter of simply adding length to the torque wrench and using the difference as a modifier. It isn't a huge deal in these examples, but for larger torque values (or it you want to be precise with in-lbs) it can cause you to deviate from the desired value by a significant amount.
The correct formula, when using an extension inline with the torque wrench, is:
Torque wrench effective length, divided by torque wrench effective length plus extension effective length, multiplied by desired torque value. The result is the torque wrench setting.
To calculate actual torque, based on the setting:
Torque wrench setting, divided by torque wrench effective length divided by torque wrench effective length plus extension effective length. The result is the actual torque value.
Top is to calculate the required setting.
Bottom is to calculate actual torque, based on the setting.
S = torque wrench setting
T = actual torque value (or "desired torque")
W = torque wrench effective length (pivot center to handle center)
E = extension effective length (pivot center to spanner center)
(If the extension is inline with the wrench, but turned back under the shaft; you can use the same formula, but the extension value is a negative number.)
However, the amount of torque being applied to the threads with the standard 2" barrel nut wrench depends on the length of the torque wrench being used. The longer the wrench, the closer the actual torque will be to the setting on the wrench (assuming it's properly calibrated).
The Army and Air Force standard is a Snap-On brand wrench (or suitable substitute) with a 14.5" pivot-to-grip length (center to center).
With that wrench, a 30 ft-lb setting results in 34.1 ft-lb on the nut.
But, if you have an 18" torque wrench, the nut gets 33.33 ft-lb.
Only if you use a 12" torque wrench, will the nut get 35 ft-lb.
Dixie, I don't think you're using the correct formula to calculate your torque values (otherwise, for instance, your 93.33 ft-lb example should be over 94 ft-lb). It isn't a matter of simply adding length to the torque wrench and using the difference as a modifier. It isn't a huge deal in these examples, but for larger torque values (or it you want to be precise with in-lbs) it can cause you to deviate from the desired value by a significant amount.
The correct formula, when using an extension inline with the torque wrench, is:
Torque wrench effective length, divided by torque wrench effective length plus extension effective length, multiplied by desired torque value. The result is the torque wrench setting.
To calculate actual torque, based on the setting:
Torque wrench setting, divided by torque wrench effective length divided by torque wrench effective length plus extension effective length. The result is the actual torque value.
Top is to calculate the required setting.
Bottom is to calculate actual torque, based on the setting.
S = torque wrench setting
T = actual torque value (or "desired torque")
W = torque wrench effective length (pivot center to handle center)
E = extension effective length (pivot center to spanner center)
(If the extension is inline with the wrench, but turned back under the shaft; you can use the same formula, but the extension value is a negative number.)
Attachments
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Dixie Gunsmithing
Moderator Emeritus
FrankenMauser,
No, it is not complicated at all. I used to run these same numbers every day, in business, when designing machinery that had to rotate certain off-center loads, and torque is simply a force multiplied by a distance. The engineering term for it is a moment. Then, you add the moments together to get the total (if there is more than one moment, and in this instance, we have two).
1 foot pound of torque, is simply 12 inch pounds of torque (twisting force) applied to the center of any shaft, fastener, etc. A torque wrench, irregardless of its length, is designed to click when you mash down hard enough with a force (force being weight), until it clicks, and if it is calibrated correctly, it will click at the amount of foot pounds you set it for, and generate that into the shaft, fastener, etc. at its center. Here, the wrench could be 24" long, and you supply it 1/2 pound to its handle, but it still clicks at a 12 pound setting because that is what it is delivering, or 1/2 pound x 24" = 12 foot pounds.
A foot pound, or 12 inch pounds, is simply a lever, connected to a central shaft, or in this case, a nut, with a pound weight hanging 12 inches out on the lever from the center of the shaft/nut. (1 pound x 12 inches from center). An inch pound is still measured at an inch away from center.
Now, any torque wrench (most are 12" or longer), when calibrated, and set at 30 foot pounds, will generate 30 foot pounds of torque, into the center of the square wrench stud, when it clicks. However, if we convert this into inch pounds, which is simply multiplying by 12, we get 360 inch pounds, or the same as if a 360 pound weight was hung one inch from the center of any shaft, nut, etc. The wrench becomes a lever, and any length on out drops the applied force needed to obtain the same desired 360 pound result. What would have took 360 pounds at 1 inch, and by increasing it to 12", would only take 30 pounds for the same result. If the wrench was 18" from the center of the shaft/nut, etc. to where the weight was applied, then it would take 20 pounds for the same result, even though the setting on the wrench says 30 Ft. Lb, because it is calibrated for its length, (and technically the moment of the wrench itself is added to the setting in the calibration, meaning a little less weight needed)
The problem arises when you add something longer onto the wrench, like this adapter, then the calibration goes out the window, if you want to know the real induced torque on the nut/shaft. You have to measure from the center of the square stud of the wrench, to the center of the shaft/nut, etc., and either deduct it for what is called out, or in Colts case, they just say use 30 Ft. Lb. with adapter, but they don't tell you that you are actually putting more into the nut because of this, due to the extension.
For instance: We have a 12" wrench, set for 30 Ft. Lb., and we know it will click when a 30 pound weight is applied to it's handle (the weight is according to the length of the wrench to achieve the same due to its setting). Then, we have a nut adapter that extends from the wrench, from the center of it's square stud, another two inches from the center of a nut/shaft; that two inches is added to the lever I mentioned above, and even though the wrench will click at 30 Ft. Lb., it actually placed a twisting force on the nut/shaft of 420 pounds at one inch, or 35 foot pounds, or 30 pounds at 14" away, when the wrench clicked, because it's leverage was multiplied over two more inches. The formula you show, is to calculate what the setting is, to achieve the same result, or what you set it at to achieve the above, for the wrench you have. You need it, because the wrench is other than 12". However, it shows that the nut, in Colt's instance, is receiving more torque than 30 Ft. Lb., even though that is what the wrench is supplying and clicking at. That two inch difference is supplying 60 more inch pounds to the nut, or 30 Lb. x two inches = 60 in. lb., and is added to it, so 30 Ft. lb. or 360 in. lb. + 60 in. lb. = 420 in. lb., then divide by 12" to get foot pounds, and it is 35 Ft. Lb. Colt doesn't say that the nut is adjusted to 30 Ft. lb., but to set the wrench at 30 Ft. lb. and use the adapter. They don't know if I picked up a 12 inch or an 18 inch long torque wrench, as either will supply 30 Ft. lb. torque or force when calibrated.
In the case above, as long as it supplies 30 pounds force to the extension when it clicks, 2 inches away from center due to the adapter, it creates an extra 60 in. lb., or 5 Ft. lb., that has to be added on to the 30. This is why I say it has to be calculated, for the tool you are going to use, when you do this, as the nut is not going to be seeing 30 Ft. lb., but more.
To get 30 Ft. lb. from an 18" wrench, it needs less weight to achieve the same result as the 12" wrench, or 20 pounds on the handle instead of 30, to get it to click at the 30 lb. setting (20 lb. x 18" = 360/12=30 Ft. lb.). 20 pounds then, applied at the end of 20" (18" to weight on wrench + 2") is 400 inch pounds, one inch from the nuts center, and if we divide by 12" to get equivalent foot pounds, we get 400 / 12 = 33.3 Ft. Lbs. This is because you are still applying 20 pounds to the handle, (no matter how long the extension or if there is none), in order to get the wrench to click for a 30 Ft. lb. setting. However, you are not, as in what Colt tells you to do, recalculating your wrench to give the nut 30 Ft. Lb. of torque., but still applying 30 Ft. lb. at 2" off center, and then adding the two moments together.
(These examples are all neglecting the weight of the wrench, and it's center of gravity moment. This, itself, will knock off the weight applied on the wrench. In other words, say an 18" overall length wrench weighed two pounds, and its center of gravity was at 9", you would add 18 inch pounds, or 1.5 Ft. lb. to each setting, which is included in the calibration, but we would still have the same result as above).
No, it is not complicated at all. I used to run these same numbers every day, in business, when designing machinery that had to rotate certain off-center loads, and torque is simply a force multiplied by a distance. The engineering term for it is a moment. Then, you add the moments together to get the total (if there is more than one moment, and in this instance, we have two).
1 foot pound of torque, is simply 12 inch pounds of torque (twisting force) applied to the center of any shaft, fastener, etc. A torque wrench, irregardless of its length, is designed to click when you mash down hard enough with a force (force being weight), until it clicks, and if it is calibrated correctly, it will click at the amount of foot pounds you set it for, and generate that into the shaft, fastener, etc. at its center. Here, the wrench could be 24" long, and you supply it 1/2 pound to its handle, but it still clicks at a 12 pound setting because that is what it is delivering, or 1/2 pound x 24" = 12 foot pounds.
A foot pound, or 12 inch pounds, is simply a lever, connected to a central shaft, or in this case, a nut, with a pound weight hanging 12 inches out on the lever from the center of the shaft/nut. (1 pound x 12 inches from center). An inch pound is still measured at an inch away from center.
Now, any torque wrench (most are 12" or longer), when calibrated, and set at 30 foot pounds, will generate 30 foot pounds of torque, into the center of the square wrench stud, when it clicks. However, if we convert this into inch pounds, which is simply multiplying by 12, we get 360 inch pounds, or the same as if a 360 pound weight was hung one inch from the center of any shaft, nut, etc. The wrench becomes a lever, and any length on out drops the applied force needed to obtain the same desired 360 pound result. What would have took 360 pounds at 1 inch, and by increasing it to 12", would only take 30 pounds for the same result. If the wrench was 18" from the center of the shaft/nut, etc. to where the weight was applied, then it would take 20 pounds for the same result, even though the setting on the wrench says 30 Ft. Lb, because it is calibrated for its length, (and technically the moment of the wrench itself is added to the setting in the calibration, meaning a little less weight needed)
The problem arises when you add something longer onto the wrench, like this adapter, then the calibration goes out the window, if you want to know the real induced torque on the nut/shaft. You have to measure from the center of the square stud of the wrench, to the center of the shaft/nut, etc., and either deduct it for what is called out, or in Colts case, they just say use 30 Ft. Lb. with adapter, but they don't tell you that you are actually putting more into the nut because of this, due to the extension.
For instance: We have a 12" wrench, set for 30 Ft. Lb., and we know it will click when a 30 pound weight is applied to it's handle (the weight is according to the length of the wrench to achieve the same due to its setting). Then, we have a nut adapter that extends from the wrench, from the center of it's square stud, another two inches from the center of a nut/shaft; that two inches is added to the lever I mentioned above, and even though the wrench will click at 30 Ft. Lb., it actually placed a twisting force on the nut/shaft of 420 pounds at one inch, or 35 foot pounds, or 30 pounds at 14" away, when the wrench clicked, because it's leverage was multiplied over two more inches. The formula you show, is to calculate what the setting is, to achieve the same result, or what you set it at to achieve the above, for the wrench you have. You need it, because the wrench is other than 12". However, it shows that the nut, in Colt's instance, is receiving more torque than 30 Ft. Lb., even though that is what the wrench is supplying and clicking at. That two inch difference is supplying 60 more inch pounds to the nut, or 30 Lb. x two inches = 60 in. lb., and is added to it, so 30 Ft. lb. or 360 in. lb. + 60 in. lb. = 420 in. lb., then divide by 12" to get foot pounds, and it is 35 Ft. Lb. Colt doesn't say that the nut is adjusted to 30 Ft. lb., but to set the wrench at 30 Ft. lb. and use the adapter. They don't know if I picked up a 12 inch or an 18 inch long torque wrench, as either will supply 30 Ft. lb. torque or force when calibrated.
In the case above, as long as it supplies 30 pounds force to the extension when it clicks, 2 inches away from center due to the adapter, it creates an extra 60 in. lb., or 5 Ft. lb., that has to be added on to the 30. This is why I say it has to be calculated, for the tool you are going to use, when you do this, as the nut is not going to be seeing 30 Ft. lb., but more.
To get 30 Ft. lb. from an 18" wrench, it needs less weight to achieve the same result as the 12" wrench, or 20 pounds on the handle instead of 30, to get it to click at the 30 lb. setting (20 lb. x 18" = 360/12=30 Ft. lb.). 20 pounds then, applied at the end of 20" (18" to weight on wrench + 2") is 400 inch pounds, one inch from the nuts center, and if we divide by 12" to get equivalent foot pounds, we get 400 / 12 = 33.3 Ft. Lbs. This is because you are still applying 20 pounds to the handle, (no matter how long the extension or if there is none), in order to get the wrench to click for a 30 Ft. lb. setting. However, you are not, as in what Colt tells you to do, recalculating your wrench to give the nut 30 Ft. Lb. of torque., but still applying 30 Ft. lb. at 2" off center, and then adding the two moments together.
(These examples are all neglecting the weight of the wrench, and it's center of gravity moment. This, itself, will knock off the weight applied on the wrench. In other words, say an 18" overall length wrench weighed two pounds, and its center of gravity was at 9", you would add 18 inch pounds, or 1.5 Ft. lb. to each setting, which is included in the calibration, but we would still have the same result as above).
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Dixie Gunsmithing
Moderator Emeritus
Below are two links for this, one the formulas and explanation, and the other is an online calculator.
On the calculator, if you use the calculated inch pounds I showed above for an 18" torque wrench, with 20 pounds on its handle, and add two inches to its length (18" + 2"), you get 400 inch pounds (20 lb. x 20"), so add it at the top. For the lever length, add 18, and for the extension, add 2, and the result should be 360 inch pounds, or 30 Ft. lb. for Y, which is the torque at the end of the wrench.
Formulas:
http://www.engineersedge.com/manufacturing_spec/torque_wrench_1.htm
Calculator:
http://www.engineersedge.com/manufacturing_spec/calculator/torque_adapter_extension.htm
Edit: If we recalculated to give the nut an actual 30 Ft. Lbs., then the wrench setting would be 27 Ft. Lb. on an 18" torque wrench, with two inch extension, but Colt says: "Torque (30 Ft. Lb.) is measured when both wrenches are used together." Before that: "Using combination wrench and torque wrench, torque barrel nut assembly to 30 ft-lb". In other words, combine the two wrenches, and watch for 30 Ft. Lb. on the wrench. If they wanted the nut at 30 Ft. Lb., they would have gave a torque wrench setting to achieve it with their combo-wrench adapter. Anyhow, one can see how it goes over, and is actually a bit higher. The 33.3 or 35 Ft. lb. isn't really critical, but the 80 Ft. lb. reading is. It can vary, according to the wrench, from 93.33 for 12" to 88.3 Ft. lb. for the 18" wrench.
On the calculator, if you use the calculated inch pounds I showed above for an 18" torque wrench, with 20 pounds on its handle, and add two inches to its length (18" + 2"), you get 400 inch pounds (20 lb. x 20"), so add it at the top. For the lever length, add 18, and for the extension, add 2, and the result should be 360 inch pounds, or 30 Ft. lb. for Y, which is the torque at the end of the wrench.
Formulas:
http://www.engineersedge.com/manufacturing_spec/torque_wrench_1.htm
Calculator:
http://www.engineersedge.com/manufacturing_spec/calculator/torque_adapter_extension.htm
Edit: If we recalculated to give the nut an actual 30 Ft. Lbs., then the wrench setting would be 27 Ft. Lb. on an 18" torque wrench, with two inch extension, but Colt says: "Torque (30 Ft. Lb.) is measured when both wrenches are used together." Before that: "Using combination wrench and torque wrench, torque barrel nut assembly to 30 ft-lb". In other words, combine the two wrenches, and watch for 30 Ft. Lb. on the wrench. If they wanted the nut at 30 Ft. Lb., they would have gave a torque wrench setting to achieve it with their combo-wrench adapter. Anyhow, one can see how it goes over, and is actually a bit higher. The 33.3 or 35 Ft. lb. isn't really critical, but the 80 Ft. lb. reading is. It can vary, according to the wrench, from 93.33 for 12" to 88.3 Ft. lb. for the 18" wrench.
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FrankenMauser
New member
There's no point in arguing about his any more.
You can continue taking shortcuts in your calculations, and I'll do it the right way.
For other people, we've provided links they can use to calculate the correct torque settings, based on their specific wrenches and extensions.
(I used to work with equipment where improperly torquing just one bolt could result in major loss of life and $46 million in equipment losses. I'm not some goon off the street...)
You can continue taking shortcuts in your calculations, and I'll do it the right way.
For other people, we've provided links they can use to calculate the correct torque settings, based on their specific wrenches and extensions.
(I used to work with equipment where improperly torquing just one bolt could result in major loss of life and $46 million in equipment losses. I'm not some goon off the street...
)Dixie Gunsmithing
Moderator Emeritus
FrankenMauser,
Do you seriously think that a website for engineers and ran by engineers is wrong? Especially, when the formula shown was a copied page from a popular engineering text book, about how to set a torque wrench using an extension? A website created by registered mechanical engineers? The same formula that is in several engineering textbooks, like Machinery's Handbook, really?
Another extension calculator from Nobar, a torque wrench manufacturer:
http://www.norbar-usa.com/calculators/torque-wrench-extension-calculator.aspx
and a downloadable calculator from Belknap:
http://www.belknaptools.com/support-library/extensions-calculator/
.
Do you seriously think that a website for engineers and ran by engineers is wrong? Especially, when the formula shown was a copied page from a popular engineering text book, about how to set a torque wrench using an extension? A website created by registered mechanical engineers? The same formula that is in several engineering textbooks, like Machinery's Handbook, really?
Another extension calculator from Nobar, a torque wrench manufacturer:
http://www.norbar-usa.com/calculators/torque-wrench-extension-calculator.aspx
and a downloadable calculator from Belknap:
http://www.belknaptools.com/support-library/extensions-calculator/
.
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FrankenMauser
New member
Just note, that the links you are providing don't even use the same formula. The Norbar and Belknap calculators use the formula I showed above. Yet the other links you provided show a formula I've never seen anyone use before.
Dixie Gunsmithing
Moderator Emeritus
They are all the same, no difference in the way they come up with the same answer I was giving, though the Belknap app is buggy.
Below, Ford Motors:
https://www.motorcraftservice.com/renderers/torquewrench/wrench_formula_en.asp?type=180degcrow
The formulas you show give you a divisor, that when multiplied with the wanted torque, gives you the setting, but its a really cut down formula of the same. This, I am in agreement with, but I use the longer formulas. The one at Engineers Edge merely give you the option of adding the two lengths, and doing it similar, and their calculator will work the same as the others.
To me, and I have read the spec from Colt, which is for the military manual, and it seems to me to say; set your wrench at 30 Ft. Lb., and add the adapter wrench, and adjust the nut. I think they may have mis-worded it, or they have one wrench specified, etc. for it. For the nut to see an actual 30 Ft. Lb., or 80 Ft. Lb., the torque setting on the wrench has to be lower than what they give, when using an adapter, and it has to be calculated by the wrench used, and is why I mentioned that they wouldn't know which wrench I would use.
A way to get it pretty close, without doing the calculation, is to set the wrench at 30 Ft. Lb., and turn the adapter 90 degrees to the left or right in an L shape. It may be an eighth of an inch or so off, but it would be close.
Below, Ford Motors:
https://www.motorcraftservice.com/renderers/torquewrench/wrench_formula_en.asp?type=180degcrow
The formulas you show give you a divisor, that when multiplied with the wanted torque, gives you the setting, but its a really cut down formula of the same. This, I am in agreement with, but I use the longer formulas. The one at Engineers Edge merely give you the option of adding the two lengths, and doing it similar, and their calculator will work the same as the others.
To me, and I have read the spec from Colt, which is for the military manual, and it seems to me to say; set your wrench at 30 Ft. Lb., and add the adapter wrench, and adjust the nut. I think they may have mis-worded it, or they have one wrench specified, etc. for it. For the nut to see an actual 30 Ft. Lb., or 80 Ft. Lb., the torque setting on the wrench has to be lower than what they give, when using an adapter, and it has to be calculated by the wrench used, and is why I mentioned that they wouldn't know which wrench I would use.
A way to get it pretty close, without doing the calculation, is to set the wrench at 30 Ft. Lb., and turn the adapter 90 degrees to the left or right in an L shape. It may be an eighth of an inch or so off, but it would be close.
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