Follow-up to Torquing Big Nuts and Bolts
Jan 24, 2018
Austin commented about my recent blog that discussed using air-powered torque wrenches to accurately tighten big nuts and bolts on farm equipment to specific torque values. He mentioned "torque-turning" fasteners (aka "torque to angle" or "angle turn") to specific torque values as an alternative to using expensive pneumatic torque wrenches or 8-foot-long, $1200 manual torque wrenches.
He makes a great point. Torque-turning is where the mechanic installs nuts or bolts to a specified, relatively low torque value, then turns the fastener a specific amount more to achieve the desired final torque. For example, I recently installed some special nuts to 200 lb./ft., then carefully turned them another 60-degrees to produce a final torque in excess of 700 lb.'ft. In this case, 60-degrees is simply one "flat" on the nut, so it was easy to measure. Other times I've been instructed to rotate a fastener an additional 90-degrees.
Engineers tell me that torque-turn is actually a better way to achieve consistent final torque compared to using a torque wrench. Some equipment manufacturers now give torque-turn specs for big fasteners, allowing mechanics and laymen to get along without buying expensive, high-capacity torque wrenches.
As Austin pointed out, it would be nice if there were tables that showed, say, that torquing a 5/8-inch bolt to 200 lb./ft and then turning it an additional 60-degrees would yield a final torque of 750 lb./ft. (those are numbers I plucked out of the air for illustration purposes.) I'm sure there are tables in engineering books or software programs that list all those values, but I haven't found them-- yet.
I'm going to keep looking, because it sure would be easier to torque a nut to 200 lb./ft. with a general-purpose, relatively economical torque wrench, then use a big iair-powered mpact wrench or a 10-foot-long breaker bar to (carefully) rotate it another 60-degrees than to wrestle with a huge, expensive torque wrench capable of torquing to 1,000 lb./ft..