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Posted: 5/4/2014 9:08:00 AM EDT
If I am using this formula to properly stake the castle nut. A= 14 B= 3.25 D= 40 Then C would = 32.46 correct? (My actual torque wrench setting) I am using the Hammerhead Rifle Tool and a Craftsman torque wrench. If I set the Torque Wrench at 40, I may actually be over torquing the nut with the added leverage. So I need to compensate for that with this formula. Is my math correct? 32.46? 
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take the torque on the nut [times] length of wrench (from the drive to middle of handle where you hold) (divided by) length of wrench (times) effective length of adapter
that equals the actual setting the torque wrench needs to be. all of this is per USAF maintenance technical data. so if you have a 12" torque wrench, and a 6'' adapter, and want to torque something 100 in-lbs you go: 100in-lbs X 12in / 12in X 6 in = 66.6 in-lbs of torque needed with that adapter. so yes 32.46 in-lbs of torque is what you need for a carbine length buffer tube castle nut. |
OP, FWIW, you can simplify torquing the castle nut by placing the adaptor at 90 degrees to the torque wrench arm; that allows you to torque to the book specification without compensation, which is 40 ft-lb +/-2. As a footnote, the TM9 also spec's MIL-G-21164 MoS2 grease on threads of buffer tube and receiver as protection from galvanic corrosion. 
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OP, FWIW, you can simplify torquing the castle nut by placing the adaptor at 90 degrees to the torque wrench arm; that allows you to torque to the book specification without compensation, which is 40 ft-lb +/-2. As a footnote, the TM9 also spec's MIL-G-21164 MoS2 grease on threads of buffer tube and receiver as protection from galvanic corrosion. Really? Wow, thank you I did not know that. So set to 40 foot pounds, hold at 90 and crank? |
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Really? Wow, thank you I did not know that. So set to 40 foot pounds, hold at 90 and crank? Quoted:
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OP, FWIW, you can simplify torquing the castle nut by placing the adaptor at 90 degrees to the torque wrench arm; that allows you to torque to the book specification without compensation, which is 40 ft-lb +/-2. As a footnote, the TM9 also spec's MIL-G-21164 MoS2 grease on threads of buffer tube and receiver as protection from galvanic corrosion. Really? Wow, thank you I did not know that. So set to 40 foot pounds, hold at 90 and crank? Yes, just turn to the click. I'd use the bottom of the torque range, 38 ft-lb, since you may wind up with some grease in the castle nut. A compendium of torquing formulas lives at Motorcraft Service, if you're curious. Technically, the adaptor needs to be under 2" for no compensation, but for the castle nut application, it's not a deal-breaker that your adaptor moment arm is 3.25" - aerospace or nuclear, yes, but there you'd be angle-torquing.
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ALL GI AR wrench/adapters are used IN-LINE with the torque wrench, and the specified torque is read ON THE WRENCH, not calculated. EVER.
You're overthinking this. If you want to torque the castle nut to spec, use a GI-like tool (one that has essentially the same distance between the nut contact and the drive socket) IN-LINE with your torque wrench and adjust the wrench/read the torque on the wrench. That's it. Remember that GI specs from the TM mean "an armorer's helper should be able to do the job with minimal direction." No math involved. |
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+1 and I AM an engineer! Quoted:
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no need for all that on a castle nut. tighten/stake +1 and I AM an engineer! I know the "need" isn't really there, but I'm OCD enough to want to torque things that have torque specs. Even when my armorer instructor specifically said "good and tight is tight enough." He did say to stake the bugger though...so it stays "good and tight." 
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Working on the other end...  Quoted:
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Torque specs go right out the window as soon as the barrel nut doesn't line up. Working on the other end... Right... my bad!!!  I don't think I ever tightened a castle nut to a specified ftlbs. Seems a bit OCD but I have my own issues as well!
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