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Posted: 6/18/2010 4:40:30 PM EDT
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Forgive me if this is an utterly retarded question.
I'm putting a FF rail on a rifle. To install and torque the new barrel nut properly, I'm using a torque wrench. The problem (?) is that with the torque wrench connected to the barrel wrench, the lever arm is extended by about 1/3. 
It would appear to me that the actual torque delivered that much further out would be about 1/3 higher than what I read on the torque wrench. Am I doing this right or is there some other non-obvious way to properly use a torque wrench with a barrel wrench? Thanks. |
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Quoted:
It's fine. Just out of curiosity what rail is it? It's a carbine length E1 rail from SWS that I'm trying to get on an AR10T upper receiver ... Though I'm discovering that the AR10T has a port door rod that's 3/16" longer than the AR10, and it's getting in the way. So much hassle over a $4 part. |
| The torque spec takes the wrench/adapter into account. Every standard barrel nut wrench I've seen has had the 1/2" drive hole the same distance from the engagement parts as a GI wrench. The specialty wrenches are similarly designed and the specs for those specialty nuts also take that extra length into account. |
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Quoted:
The torque spec takes the wrench/adapter into account. Every standard barrel nut wrench I've seen has had the 1/2" drive hole the same distance from the engagement parts as a GI wrench. The specialty wrenches are similarly designed and the specs for those specialty nuts also take that extra length into account. I'll buy that, provided you are dealing with a standard AR. If the wrench has an extended handle as shown, no. Torque value will not be accurate. Because I'm ignorant and have to make my own wrench. I referred to the easiest formula I could find. It's included with Craftsman Torque Wrench's 458 |
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Quoted:
Quoted:
It's fine. Just out of curiosity what rail is it? It's a carbine length E1 rail from SWS that I'm trying to get on an AR10T upper receiver ... Though I'm discovering that the AR10T has a port door rod that's 3/16" longer than the AR10, and it's getting in the way. So much hassle over a $4 part. I also ran into the same problem with the "T" length port door rod. If you have a grinder or cut-off wheel, just grind/cut it down to the correct length, making sure the edges are smooth and insert the ground end first... |
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I also ran into the same problem with the "T" length port door rod. If you have a grinder or cut-off wheel, just grind/cut it down to the correct length, making sure the edges are smooth and insert the ground end first... I did have to replace the AR10T port door rod (4 3/8" long) with an AR10 rod (4 3/16" long) to get it to fit. Did you also end up with a small gap between the rail and the upper receiver? Is this normal? 
I put a detachable carry handle on top bridging the upper and the rail to help with alignment. It fits, though the top rail clearly has a slightly wider than normal gap between the high points on the upper & rail. Just concerned that the gap shouldn't be there. This was with the barrel nut torqued to near 80 ft-lbs so there isn't any more room to get the nut/barrel/rail closer to the upper. The rail itself is super nice. I may have to get a black low-profile gas block though, since the stainless rail gas block I have now just looks weird and out of place sitting in front of the E1. |
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Quoted:
Quoted:
The torque spec takes the wrench/adapter into account. Every standard barrel nut wrench I've seen has had the 1/2" drive hole the same distance from the engagement parts as a GI wrench. The specialty wrenches are similarly designed and the specs for those specialty nuts also take that extra length into account. I'll buy that, provided you are dealing with a standard AR. If the wrench has an extended handle as shown, no. Torque value will not be accurate. Because I'm ignorant and have to make my own wrench. I referred to the easiest formula I could find. It's included with Craftsman Torque Wrench's 458 But doesn't that forend come with instructions that include the torque the manufacturer wants for their barrel nut? As I recall, Daniel Defense float rails have a different spec for torque because of their special barrel nuts. |
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I thought you were supposed to set the wrench at a 90 angle to the torque wrench to keep the distance correct and get an accurate reading... ? http://kevinholman.com/byor/ar10noveske/torquenut.jpg Picture taken from a post from Falarak... Nope, that's wrong. At least for standard barrel nuts and standard wrenches, you keep the torque wrench IN LINE with the barrel nut wrench. I'd refer to the instructions that came with the forend to be sure, but I think it's that way with all barrel nut wrenches, including the specialty ones. |
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I don't know if the torque spec takes into account the increased torque arm of the adapter or not. I do know that for the actual torque on the barrel nut:
Actual torque = Indicated torque X (length of torque wrench + length of adapter) ÷ (length of torque wrench) The length of the torque wrench is the distance between the center of the square drive to the point where force is applied (approximately center of handle). The length of the adapter is the distance between the center of the square drive hole and the center of the barrel nut (center of bore). The formula for torque (ignoring friction) is T=Fd or Torque = Force X distance, where distance is the total length or radius of the torque arm. To include the effect of friction, T=KFd where K is the dynamic coefficient of friction. I do not know what K is for a greased barrel nut. In actuality the acceptable torque range for an AR-15 barrel nut is so wide that it doesn't make sense to get worked up about the details. It's the position of the gas tube hole that's going to determine the final torque. The most a torque wrench can do is help you choose the correct hole! |
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Correct on the formula. Use the torque wrench and the tool of choice such that they form a straight line. The set up shown in the picture by Buck_Naked will only produce a ambiguous answer. Sorry. Theoretically, a person could apply a torquing moment using that set up and never actually turn the tool of choice. I realize that the odds of doing so are pretty slim; I mention it only because of the odd effects that might arise from using that set up.
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| Just to add some fuel to the fire...I am a powersports technician (motorcycle/atv/snowmobile) and every manufacturer tells you to put your torque wrench at a 90 on the tool as shown in the pic. Its easier for them to make the tool and and instruct that it be used at a 90 degree then try to calculate the length between the tool and the drive hole to get the proper torque. This being said I know nothing about Ar-15 barrel nut torque or the tools used to apply said torque. |
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Just to add some fuel to the fire...I am a powersports technician (motorcycle/atv/snowmobile) and every manufacturer tells you to put your torque wrench at a 90 on the tool as shown in the pic. Its easier for them to make the tool and and instruct that it be used at a 90 degree then try to calculate the length between the tool and the drive hole to get the proper torque. This being said I know nothing about Ar-15 barrel nut torque or the tools used to apply said torque. Same here, certified by American Honda and American Suzuki - and you are absolutely correct. Everyone that says keep it inline with the wrench - not correct for proper torque. Anybody that wants to get mad about it can research the proper way to use a torque wrench - and start using it properly. Buck_Naked is right on it. |
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For an adapter that is very short compared to the wrench, attached at 90 degrees to the wrench, the distance from the handle to the fastener is pretty close to the same as the wrench alone, so no adjustment would be necessary for an approximate measurement. But as the length of the adapter increases, error related to the application of force at the wrong angle increases. This error is caused by the fact that force applied to the handle is no longer tangent to the radius of the wrench/adapter assembly. Visualize an extreme example of a one foot wrench with a six foot adapter. Very little of the force applied to the wrench handle would actually be applied to torquing the fastener.
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