What is the golden rule for torquing nuts and bolts?

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Discussion Overview

The discussion revolves around the best practices for torquing nuts and bolts, exploring various approaches, recommendations, and the complexities involved in determining torque specifications. It encompasses both theoretical considerations and practical applications in mechanical engineering contexts.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest using a torque wrench and following the manual for critical situations, while others propose a more informal approach, such as 'wrist-tight' torque.
  • One participant emphasizes the importance of understanding the elastic limit of materials and the potential for permanent deformation in certain applications, particularly with automotive head bolts.
  • Another participant notes that there is no universal golden rule for torque, as it depends on the specific loading requirements, material properties, and thread characteristics of the fasteners.
  • General torque recommendations from manufacturers are mentioned, but it is highlighted that these are not absolute rules and require careful analysis.
  • A participant humorously references the "German torque" (gutentite) as a fallback method when unsure.
  • There is acknowledgment of the variability in the fit of nuts and bolts, which can affect the torque application.
  • Clarifications are made regarding the meaning of 'wrist-tight' to avoid misunderstandings about safety and the risk of damaging components.

Areas of Agreement / Disagreement

Participants express differing views on the existence of a golden rule for torquing, with some advocating for specific techniques while others argue that torque specifications are context-dependent and variable. The discussion remains unresolved regarding a definitive approach.

Contextual Notes

Participants mention various factors that influence torque, such as material grade, length, and lubrication, indicating that assumptions and definitions are crucial to the discussion. There is also a reference to the limitations of general torque recommendations.

wolram
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What is the golden rule for torquing nuts and bolts?
 
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If it's a critical situation, use a torgue wrench and consult the manual. Otherwise, my rule is 'wrist-tight', ie: thumb, forefinger and bird-finger cradling the head of the ratchet and twist as much as you can from there (if you have a normal sort of grip). There is no substitute for followng the manual, but wrist-tight is always safe.
 
wolram said:
What is the golden rule for torquing nuts and bolts?

What grade? How long? Why isn't this in mechanical engineering? Who's on first?

0.1% is the elastic limit for most steels --- once you've "set up" against the pieces you're holding together, 0.1% of the bolt length divided by the thread pitch in turns; depending on diameter, grade, finish, and lubrication, you'd best hit a handbook --- I ain't going to type one. If you're playing with automotive head bolts, you'd best find out if someone stuck you with "torque to yield" specifications --- 1% elongation or more, resulting in permanent deformation --- USE ONCE ONLY; this is one of Detroit's cost cutting measures --- machine measures torque while tightening bolt and quits once it is constant vs. no. of turns completed --- torques to failure about 10% of the time, but, what the hell, that's good enough for the consumer market. The idea was that it results in equal tension on all head bolts --- great, if they're "dogboned" --- not so great if they aren't --- they fail at the thread root with a greater variation in tension than results from variations in thread friction using a torque wrench.
 
:bugeye: Wow! Awesome post, Bystander. I never saw that stuff before.
 
Danger said:
:bugeye: Wow! Awesome post, Bystander. I never saw that stuff before.

I quite agree thanks Bystander, i have all ways had respect for the nut, bolt,
thread, it is amazing how much variation there is in say a 10mm nut and bolt,
some times you can (rock) the nut on the bolt, other times the nut can be a
(tight) fit.
 
There is no goloden rule for torque. Technically, the torque is related back to the loading the joint must withstand. That load combines with the material of the fastener and the effective thread area. They are always different.

I have seen general torque recommendations given by fastener manufacturers, but even they say that it is not a steadfast rule. Analysis should always be done.
 
Danger said:
There is no substitute for followng the manual, but wrist-tight is always safe.
I just noticed that I used stupid phraseology there. I did not mean that it's safe as in "it won't come apart"; I meant that there's little chance of damaging the bolt or nut or stripping the threads of the component. Sorry if there was any misunderstanding.
 
I guess when in doubt, the German torque (gutentite) is always something to fall back on.
 

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