Just watching a bearing hub replacement which required a 46 pound-feet of torque with an additional 120 degrees to get it done proper.

Why did they add the angle torque addition instead of just giving the adjusted foot pound of torque? For example, perhaps 46 pound-feet + 120 degrees would finally end up becoming 80 pount-feet of torque. So why not just give us a spec which says 80 ft-lb ( + 0 degrees ) ?

I guess in essence the question is: is there 1:1 relationship between torque+roation with a specific torque value?

  • 3
    I don't know the specifics on the answer but feel it may be related to "stretch bolts" (i.e. single use bolts that are designed to stretch when torqued up correctly). Mar 23 '17 at 16:13

@Steve Mathews you are correct : it is to with the stretch and yield of the material used in the bolts, a search on google gave this site amongst other explanations which, fortunately leaves out the maths used in stress calculations. https://user.xmission.com/~kd7olf/torque.html

Do note the warning about NOT re-using that type of bolt.

  • Fascinating, that explains in quite nicely. So torque measurement is a guess to the point at which a stretch bolt will start to stretch, and then the rotation will be able to determine the exact stretch of the bolt and when combined with understanding of the bolt threading, material, thickness, etc, then you can get it at near maximum stretch so it holds. BTW the guy in the vid reused the stretch bolts :)
    – Chris
    Mar 23 '17 at 16:40
  • Then, as per the explanation, that is not smart and I have seen re-used bolts break before they get to the required value.
    – Solar Mike
    Mar 23 '17 at 16:55
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    @Chris The torque spec isn't a guess. In fact, the torque spec is the ideal value for a bolt's preload force. The problem is that it's difficult to accurately read fastener torques because of differences resulting from lubrication, under-head friction, and tool repeatability. Using an angle, however, you can predict reasonably well the preload the fastener will provide and measure the angular difference very accurately.
    – Hari Ganti
    Mar 23 '17 at 22:19

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