Why not 26.5% or 23.2%? Why is that number special and how was it derived?
I agree, there however is a lot of REAL science to it.
You don't get out much do you?
Why did this wheel stud break? Metallurgy issue?
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Why not 26.5% or 23.2%? Why is that number special and how was it derived?
I agree, there however is a lot of REAL science to it.
You don't get out much do you?
25% has always worked for me and millions of others. No need to be exact. I come from a family of machinists and gearheads. And having worked on all kinds of heavy as well as light fasteners, 25% torque reduction on lubricated threads has never resulted in a fastener failure.
I really don't care about the real science. I only care that my wheel stays mounted and lugs are secure.
I have been to many many tire shops over the last 50+ years. Since the last few dozen or so I have noticed a torque wrench being used on all wheels being mounted. I get out enough to research and know that a repair job is going to be done right before I ever let someone work on my vehicle. I already know what the torque spec of my studs are going to be before walking into the shop. On the little sheet of paper called a receipt the torque specs are on it.
Basically stating the obvious, adding a lubricant to either the thread or bottom of the head will alter the "clamp load/tension attained" for a specific torque spec
Input torque here being you turning a wrench
In this test Lubing the threads increased the clamp load by 18%.
Clamp load being how much stretch you got out of the bolt/stud (bolt tension is equal to the clamp load ).
Thus if you lubricate your threads decreasing your torque spec appropriately will achieve equivalent" "non lubricated clamp load" when OEMs specify "Clean and Dry threads"
Theres nothing like vague anecdotal blanket statements to illustrate fully why most of these problems exist in the first place. Carry on.
Of that there is no doubt in my mind
Respectfully, their article is written very badly and this is "technically accurate (as per their single test) but cannot be stated as a technical axiom to be universally applied.
All torque specs start out dry as the specified tension due to thread class, selection, surface coating etc. Ones who give wet readings are doing so just based on their individual circumstances and even then every different lubricant will have a different affect on the COF so no universal standard is possible.
There is no such thing as "equivalent non-lubricated clamp load". Its a made up term with no possible value mainly for the reason stated above but also for hydraulic effects resisting the "torque' that are indistinguishable for the measuring device.
The short simple absolute answer is any lubrication induces an unknown and incalculable variable into the fastener tension equation when TORQUE is the measurement of stretch since it is IMPOSSIBLE ( that means what it means) to correlate any torque measured any way known to exist and correlate it into fastener stretch. It is equally IMPOSSIBLE to decouple and state any "value" or contribution of any lubricant because of all the other corresponding and complimentary variables.
Just stating the facts.
You're confusing what they should do with what they actually do, too often. I've seen them grossly overtighten the lugs with an impact driver, then go around with a torque wrench only to confirm they aren't too loose---which of course they're not. I always check when I get back from such places and loosen them, if needed. Of course a few shops actually get it right.
I have seen them torque the studs and there is always some movement after spinning them on with air.
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What problems might that be? A little common sense goes a long way to preventing a fastener failure. I dare say I don't even use a torque wrench on every fastener. I and many others have fabricated, assembled, and tightened down with nothing more than the hand tools on hand. Many have also installed wheels in the field with nothing more than a lug wrench on hand with zero problems or failure. Works for me!
I agree, this was an example under their specific case. But it explains where this "Rule of thumb" comes from with some background albeit not correct from an engineering standpoint.
100% agree, if you do purchase a quality anti-seize the manufacture can provide a "K" value.
Thats why I put it in quotes
its my made up term for my post to drive home that you could/should reduce input torque for lubricated threads.Torque as the measurement as stretch is not very precises due to the frictions involved, lubricated threads can produce more accurate clamp load.
T=KDF can be used to roughly figure out the reduction of torque required if you know your lubes K value. For example assuming a dry electroplated zinc bolt (common for automotive) is .22 simply applying loctite silver anti seize (.18) will require an 18% reduction in torque.
But doesn't a dry thread ALSO introduce an un-known? I mean, I live in the salt belt and after a few years I would assume thread surfaces are not the same as new. They are going to be pitted and at a higher friction. No wire brush is going to make them new either. So in effect, there is no "perfect answer" to this. Being in the salt belt, I lube my lugs and back off a little. And for the OP: Your stud broke becase you have been consistently over-tightening them for years. Don't do that.
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Respectfully, no they cannot- it is physically impossible for them to do so because it would literally require a "K" factor for every deviation of a thread type over an infinite range of sizes and other factors comprising the COF of a specific joint or fastener.
Again, respectfully and in no way directed toward you or any one in particular, "Torque" as a measurement of "stretch" is physically IMPOSSIBLE (that's the only applicable word) to correlate- the two things are forever radically different and do not correlate in any way. What you do get is 'situational" and at best "coincidental" based on an average.
Even when you calculate a torque spec for a given joint and its an accurate relative measurement- you change even 1 value of the joint ( rust, thread wear, dirt, damage to the bolt head bearing surface, change the joint load and the list goes on) then the original torque spec is rendered meaningless.
Given the fact that without all the other requirements of the COF ( which is difficult to do even in laboratory conditions) its still nothing more than an anecdotal guess. Save the effort of building a meaningless math problem and just go "eenie, meenie, miny, moe"- you will have the same level of accuracy and be much quicker.
ABSOLUTELY, even down to the consideration of "are these threads rolled, machine cut or tapped?"
That's EXACTLY correct although I would take the word perfect out and put accurate or true in the place.
This is why without UT, count or angle measurement- you simply cannot know the tension you are putting on the joint proper.
No one can.
People making wrong decisions based on false information leading to possibly damage or injury ( or both)
Of course, and your point?
So our takeaway on all this is to not to trust our instincts or years of experience and throw common sense out the window. Only then will you be able to torque properly by using scientific formulas.
So much for installing wheels. I better get my toque wrench calibrated, remove and replace all my lug studs and bolts as they may have already stretched beyond the point of elongation and the TTY point of the stud has been exceeded.
So much for installing wheels. I better get my toque wrench calibrated, remove and replace all my lug studs and bolts as they may have already stretched beyond the point of elongation and the TTY point of the stud has been exceeded.
Well yea pretty much everything is anecdotal if you are not in a lab... torque specs have there issues as you have illustrated. OEM's are perfectly fine with issuing dry torque values where preload can vary up to +/- 25% and their joint calculations obviously take that into account.
Simply reducing torque when applying lubricant to the threads is 100% sound, yes there is still uncertainty but, you can mitigate some of that with a known "K" value as I mentioned previously.
ABN_CBT_ENGR, I am curious how do you tighten your lug nuts?
No freaking clue. Rock hard tires. I had to get two other gauges to confirm.
Fair question, Impact wrench and a torque stick ( unless in the field and a breakdown then its the educated arm method).
Keep the stick with the vehicle should it happen on the road. The 2 shops I use normally "generally" go through the motions of properly torqueing but I "help" them on mine.
I don't consider a lug a "critical fastener" (in the sense and definition industry applies to that term) and "evenness' of tension in a centrifugal application is more critical than actual load as ( in normal usage) a lug sees virtually no significant radial loading (measured against design stress) but more axially.
I see your reading comprehension skill is right up there too. Nobody said or implied that at all.
He pointed out your reading comprehension already so I have to point out to you that he said nothing about carrying a torque wrench in his vehicle.I would say taking a torque wrench with you in a vehicle is a bit over the top. But if it makes you feel comfortable then
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