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Posted: 5/12/2012 3:15:09 AM EDT
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I have watched about a dozen videos from the makers of free float rails and hand guards and all of them are using the TW wrong. Barrel nut torque is commonly stated at 30-80 foot lbs which is a very wide range. This is a given, but the TW should be inserted at a 90 degree angle in the wrench to get the correct torque. If the entire TW and socket head are inline the additional length must be taken into account and the wrench set accordingly. You have to measure the extension, do the math and go from there. The easiest way to get it right when using the big crow's foot is put it on the wrench at a 90 degree angle to the TW head, not inline, then the torque setting is correct.
I am a retired armament specialist and crew chief and clicked a TW for 20 years on F16s, they taught this stuff in tech school. I wrenched everything from M61s to PW220/220Es so I understand TWS and can twist safety wire. So why are all the folks using the tools incorrectly? |
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Quoted:
I have watched about a dozen videos from the makers of free float rails and hand guards and all of them are using the TW wrong. Barrel nut torque is commonly stated at 30-80 foot lbs which is a very wide range. This is a given, but the TW should be inserted at a 90 degree angle in the wrench to get the correct torque. If the entire TW and socket head are inline the additional length must be taken into account and the wrench set accordingly. You have to measure the extension, do the math and go from there. The easiest way to get it right when using the big crow's foot is put it on the wrench at a 90 degree angle to the TW head, not inline, then the torque setting is correct. I am a retired armament specialist and crew chief and clicked a TW for 20 years on F16s, they taught this stuff in tech school. I wrenched everything from M61s to PW220/220Es so I understand TWS and can twist safety wire. So why are all the folks using the tools incorrectly? IDK maybe because none of them are retired armament specialist and/or crew chiefs  You make a good point though.
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Due to the wide range of torque, it'd be real hard to mess anything up. In most cases the barrel nut does not even require 70lbs.
Granted I have only done 12-13 builds now, so my sample size may be too small. What kind of variance are we talking about? 1lb, 2lbs, ect..... |
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Quoted:
Due to the wide range of torque, it'd be real hard to mess anything up. In most cases the barrel nut does not even require 70lbs. Granted I have only done 12-13 builds now, so my sample size may be too small. What kind of variance are we talking about? 1lb, 2lbs, ect..... With an extension past the wrench drive you will increase the torque applied to the nut relative to your intended value. So it will be tighter then what you want. Of course this all depends on the length of your wrench and length of barrel nut tool. But the values can be off by quite a bit! Keeping the tool at 90 degrees keeps the length of the handle to the tool as close as possible to the length from the handle to the wrench drive. It will still be off, but significantly less, again depending on your tools length. EDIT: Here is a simple calculator I found. http://www.engineersedge.com/manufacturing_spec/calculator/torque_adapter_extension.htm Maybe plugging in a few different numbers will explain it better then I can haha |
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Good point OP, but as stated, I believe most experienced builders strive to stay in the lower part of the torque range and the offset distance on most of these barrel nut wrenches is short.
Would be easy to kick the TW over to a 90, though. From the M16/M4 manual.... 
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Yeah I've seen people say that the distance of the cutout is taken into account...but I think I have also seen wrenches that come with instructions to put the wrench 90 degrees to the handle of the wrench
you can see a guy doing just that on the bottom of this page http://www.shootingillustrated.com/index.php/10480/installing-an-ar-15-barrel I used a PRI barrel nut wrench...and their website shows to put the torque wrench on parallel with the extension http://www.precisionreflex.com/Content.aspx?PAGE=How%20to%20-%20%20Forearm%20Assembly%20with%20Front%20Sight%20Post |
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There we have it, the weapon's own manual shows the tool being used wrong or the torque value stated takes into account that set up which would be very odd indeed. I know about assumptions, but I always assumed the give torque value took into account the issued wrench. It doesn't really make sense to supply a value that requires a correction when you supply the tool and the manual. |
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No, torque values should given as an absolute that way if the work requires cobbled together or non-standard tools the guy doing the work can set the wrench accordingly. Now, this may be a MAJOR difference between USAF aircraft tech data and USA armorers manuals. I will have to ask the CATM guys at work how they do it. (I am still employed by the USAF)
BTW, this is pretty much a mute point because the torque range is so broad it is almost impossibles to screw it up. Though over torquing ham fisted work could crack an upper. Set it to 30, do the tighten loosen routine, torque it to 30, if not lined up, set it to 80 and align the holes without tripping the wrench then you are good to go. If you trip the wrench before the holes are aligned, face or shim the upper a hair and try again. On a side note, most torque values on aircraft are in inch pounds, the AR values are VERY broad to say the least. I mention my background to validate my experience, nothing more. |
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You are absolutely correct, but the 2 additional inches (or so) in lever arm doesn't make that much difference with the torque range involved. 80 up to 90 lb/ft is not a big variation since the current receiver diameter and thread pitch probably have more of a design margin than an extra 10 lb/ft of torque.
If anyone wants the formula for correcting the torque value, let me know and I'll email it to you. |
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Here is an online calculator for use of extensions on a torque wrench.
http://www.belknaptools.com/support-library/extensions-calculator/ |
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