Question: What number of ft./lbs. Indicated on my torque wrench will give me the Actual ft./lbs. of torque I want on my bolt when I use an Extension ? There's gotta be a formula.
Answer: There is, I=A/(1+E) . I = Number of ft./lbs. indicated on your torque wrench's scale. A = Number of ft./lbs. of torque you want on the bolt. E = Length of extension,center to center,in feet (example: 4 inches = .333 feet or 4/12 = .333 feet). The kind of extension we're talking about makes your torque wrench a longer assembly, not an L-shaped assembly that you would get with a common ratchet extension. The extension should form a straight line with the torque wrench.A small deviation from straight should be okay,but take note,ALL deviations from straight will result in a bolt that is not quite as tight as the formula suggests.We're talking small amounts that need not be accounted for. Ideally,on a beam torque wrench,you would like the handle pivot,the drive end of the torque wrench and the center of the bolt to form a straight line when you reach desired torque.
Example:I want to torque a nut on the Starship Enterprise's,Transporter's Pattern Recovery Tank to 100 ft./lbs. but it's tight in there.I'll get a 9 inch extension (are you listening Deanna Troi)for the torque wrench so I can slip it into that oh so tight slot.Now the question is what indicated reading on the torque wrench will I need to reach the climax of 100 ft./lbs on the nut.Well the formula again is I=A/(1+E)or I=100/(1+.75)where 100 is the number of ft./lbs. I want on the nut and .75 is the length of the extension(in feet).Now it's I=100/1.75 or I=57.14 ft./lbs. Soooo,if I have my extension on straight and it's reasonably stiff(flexes but returns to original shape after use)and my three reference points(handle pivot,square drive and nut)are close to in line when I'm pulling hard enough to show 57.14 ft./lbs on the scale on my torque wrench then I know my nut is properly torqued,Deanna's should be and I need a cigarette.
Now for some editorial comment,the length of the torque wrench,the size of the bolt,the diameter of the thread,the number of flats,the size of the socket and my oldest child's birthday all have one thing in common.None of them have anything to do with calculating the correction factor when using an extension on a torque wrench.I googled "torque wrench formula" and visited six websites that wanted to factor in the length of the torque wrench in their extension correction formulae.I had no idea the web is this fouled up!Cheers IsayItUcanBelieveIt
