Please bear with! Consider the following: Take a hardened steel ball bearing and place it in a glass tube 10 feet long and closed at one end. Stand the tube on end on a thick flat steel table. Hold the ball bearing up at the closed end (top of tube) with a magnet. Evacuate the air in the tube. (no air resistance) Now remove the magnet. The ball drops to the table and rebounds. Agreed? It should be obvious that the ball will not rebound to the initial full height (10'-0") but it will rebound some fraction of the initial drop height. Successive rebounds will be less and less until the ball ultimately rests on the table. Agreed? Why does this happen? Because every solid material has an associated mass, moment of inertia, and modules of elasticity. No collisions are 100% elastic. Energy is consumed (redistributed)in deforming the ball/table material when it bounces. No free lunch! Potential energy (height) is converted to heat, sound, vibration, etc. Socket extensions also deform when torque is applied, but, they deform mostly torsionally. It takes energy to do that. As long as the extension is not deformed beyond its elastic limit, it will return to its original condition when the torque is released. Tightening a bolt is a dynamic process, not static. Strictly speaking, the pure rules of statics don't apply until the fastener stops moving. An excessively long socket extension will effect (slightly reduce) the final torque on a threaded fastener at higher torque settings on any given torque wrench. Only in extreme cases is it significant. (racing applications, rocket engines, jet turbines, nuclear reactors, high pressure hydraulics, etc.) If necessary, it's best to use the shortest extension possible.
What's more important is that the torque wrench is setup the same way and the torque method is consistent. If a series of fasteners is torqued in a given sequence, the fasteners should all be of the same grade, the same diameter, the same thread pitch, the same class of fit, and the same length. (if possible) If the specs call for clean and dry threads, a special lubricant (corrosion), anti-seize compound, teflon tape, thread locking compound or any other special treatment, it should be applied consistently to all the fasteners in a given application. (unless otherwise noted) Not doing so can have a major effect on the (hopefully) ultimate long term uniform clamping force(s).
Chum lee (over 40 years experience in structural, mechanical, and civil engineering)
