Originally Posted By: TomYoung
Your link goes to the ASM catalog. I would be interested in seeing the actual document.
Sorry, here's a link to the book
here. on Google books. You can preview a lot of it. This chart is pulled from 674, if it's available in the preview.
Originally Posted By: TomYoung
But in the real world, I would question what "feel" really means. Is my "feel" as accurate as yours? Does this vary from individual to individual. Is the assertion that you generally do better asking a person to "tighten this bolt to 50 lb ft" without a torque wrench? Do you want your engine rebuilder to operate this way? And what about getting the lug nuts adequately tight. I have been a passenger in a car where the front wheel came off because the lugs were too loose. And is the offender the "click" type torque wrench? If so, is the "Snap-On" in the same boat as the "Harbor Freight?"
To answer these question in order:
-it depends. There have been volumes of research on written on measuring the accuracy and repeatability of bolted joints, and 'operator feel' is determined differently depending on who's doing the measuring. Generally, it's an operator tightening to a specified friction torque specification with a regular wrench. You're right, there's a ton of variability. But the takeaway is that there's a ton of variability using a friction torque wrench as well. There's also not a clear advantage of an 'experienced operator' vs. an 'inexperienced operator'. The only real tread I've seen among the many studies is that experienced operators tend to over-tighten, inexperienced tend to under-tighten.
-the assertion is that telling someone to tighten a bolt to 50 ft lb and having them tighten a bolt with a clicker-type torque wrench to 50 lb will have roughly the same result
-I want my engine re-builder to use appropriate fasteners for the job, like load-indicating washers or TTY bolts where appropriate, since they're much more accurate. I also want him to use the angle-torque specifications for bolts where bolt tension is critical, since these specs are generally given for tension-critical joints.
-lug nut specs are generally 80-100 ft lb. There's so much wiggle room in the spec that the most likely reason a wheel will come off is that someone simply forgot to tighten the bolts! If you tighten them to "really effin' tight', which is my spec for lug nuts, you'll never have a wheel fall off... Forget about lug nuts though; when someone is installing a giant metal plate and 11 screws in my wrist, I want them using something more accurate than a torque wrench! (don't worry, they do-they use a depth gauge).
-arguing about "Snap-On vs Harbor Freight" when it comes to clicker-type torque wrenches is analogous to talking about "which truck scale should be get to measure these feathers". Sure, the higher-quality torque wrench may have better accuracy, but the dominant source of error, by several orders of magnitude, is the measurement method itself, not the wrench. Some people like to fool themselves into thinking that if they buy a really expensive clicker torque wrench that they'll be able to tighten bolts with great accuracy, and that's simply not true.