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Posted: 4/28/2013 1:33:45 AM EDT
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Having been a Jet Engine Mechanic in the Air Force and having to use torque wrenches with offset wrenches and cheater bars we had to work out formulas when torquing anything that wasn't an exact 90 degree angle and where the center of the torque wrench head wasn't directly in line with the screw, bolt or nut being torqued brings this in question. When the manual (we'll use the AR15 for this exaple) says to torque the buffer tube or buffer tube castelated nut to 35 foot pounds does this torque value already factor in the difference that the center of the torque wrench head is not in a direct 90 degree angle relationship to the part being torqued when using the AR wrench in combination with a torque wrench? I understand that it isn't critical...I'm just curious? |
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To the best of my knowledge torque specifications are true torque measured at the fastener.
Offsets are our problem to figure out. Think about it, manufacturers have no way of knowing what combination of wrench/adapters are being used and while one combo may give 35 ft/lb another may give 60 ft/lb. I have a dedicated castle nut wrench that is about 10" long and once the nut contacts the plate I give it about an eigth of a turn. Pulls up plenty snug and stake the plate to the nut. The only critical torque on an AR is the barrel nut. Most call out 40 ft/lbs on a moly lubed thread (grease or anti seize) then additional torque if required to line up the gas tube notch/hole not to exceed 80 ft/lbs. You can throw a cat through that kind of range! |
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Per the TM, torque for the barrel nut and other torqued fasteners are measured at the 1/2" attachment point of the GI multi wrench. If using other than a GI multi wrench, feel free to calculate and apply an offset.
From a practical standpoint, there's really only one notch you'll ever get to line up on the barrel nut within the specified torque range, using the specified procedure (tighten, loosen, tighten, loosen, tighten, loosen, tighten to final torque and lineup). The other torqued fasteners such as the muzzle device and telestock nut have a very broad range of acceptable torque, and will tend to time within the acceptable torque range. |
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