torque wrenches

[needforspeed66gt]

Considering that the bolt tightening accuracy of a torque wrench is only +- 30%, does it really matter which torque wrench is used?

Well the torque wrench is accurate in that the bolt has "X" ft/lbs applied to it, the variance in clamp and stretch load is debatable, mainly by those who want to sell you an alternative technology.

I personally have seen 5-10% at the most on rod bolts where stretch is measured at the same time as torque applied. The 30% figure is used to scare people into buying a different tool, if you grab a mixed bag of chinese non-graded hardware, torque it dry... then grab an ARP 2000 with the correct lube and torque it - then you may have a 30% difference in clamp load applied. But same hardware from the same batch with good lube and the same torque procedures....I will have to see some data to back up that claim, cause I'm not buying it.

[David Redszus]

Considering that the bolt tightening accuracy of a torque wrench is only +- 30%, does it really matter which torque wrench is used.

Well the torque wrench is accurate in that the bolt has "X" ft/lbs applied to it, the variance in clamp and stretch load is debatable, mainly by those who want to sell you an alternative technology.

The torque that we measure is actually frictional resistance. Factors that influence frictional resistance are method of thread cutting, lubrication, clearances, temperature, coefficient of friction of plated surfaces, washers and bolt head as well as threads.

There is no debate among fastener engineers who really understand how hard it is to torque a bolt properly. The +- 30% accuracy value has been well established by the fastener industry.

[Speedbump]

So, David, what you're saying is other than ease of adjustment and repeatability, a torque wrench is like the nite light in your room when you were a kid... doesn't do much but makes you feel a lot better?
I respect your opinions and am also fascinated by fastener science the more I learn, but what do you do?
Do you use rod bolts that are stretch guage friendly on all of your builds, considering use, time and money? What about fasteners almost as critical like head bolts/studs where stretch can't be measured? Other than getting rolled threads, good washers, quality lube and a "good" wrench, what do we do?

[Cammer]

Opening up the whole torque/tightening/tension subject field is a bag of snakes!

Tightening by feel = +/- 35%
Torque wrench= +/- 25%
These figures are within a few percent of those quoted by most engineers.

I have seen experienced assemblers tightening by feel beat torque wrench numbers!

Measuring bolt elongation is good for +/- 5%

Thread and head lubricants/aids are another controversial subject. Looking just at oil; we find it may not be able to stop metal to metal contact, may run out of joints, may burn, and thus compromise the assembly.

Various offshore "bootleg" fasteners presenting name brand markings adds to the confusion. We are now seeing USA brand name fasteners and tools with quality problems. Are they sacrificing quality to compete with the cheap imports?

I am concerned with low quality fasteners falling into the hands of shops not having the resources and equipment to test.

I have checked locally sourced import Grade 8 threaded fasteners which performed poorly and exhibited various dimensional and physical problems. The global economy is great! Sure it is! Anyone remember the radioactive patio furniture from Mexico?

Engineers are constantly looking to find the best ways to tension threaded fasteners. Automakers thought the torque-to yield/angle method was the solution but this has not been the case.

Individual applications call for individual methods.

I wish this subject was easier to define but that is not the case.

[racecar100]

I recomend a flat beam torque wrench.. Most round beam, clicker, dial, and digital accurateness is 7 to 10% The Flat beam is 2%.

[Sir Yun]

i have to place the 30 % +/- in perspective.

i'll spare y'all the formulas but when you tighten a M12 8.8 grade bolt to 60% of its yield strenght.


the huge variance is caused by the large effect of friction (mu) of the thread.
with a mu of 0.15 =/- 0.05

you need 40 NM for the tread friction + 38NM for the bolt face to surface..

if you have zero (mu=0) (which is pure theory as the bolt would not self lock anymore)

the torque needed to pull the bolt to 60% would be .. 9 NM.

ergo

88% of the torque is used for the friction.

the friction would not be a problem per se ..as long as you dont exceed the Von Mises equivalent stress factor: basicly the combined force of twisting and pulling.

it is the variance that is the killer.


good steel has a very thin layer of oxide which if damaged causes galling causing an increase in Mu..but in unknown amounts.

supposedly proper lubing with MoS2 lowers mu to about 0.12 +/- 0.02.

still not great but better nonetheless.

ergo:

measure bolt elongation if possible.

here are some calculators for this kind of stuff:

http://www.tribology-abc.com/calculators/default.htm

[David Redszus]

What about fasteners almost as critical like head bolts/studs where stretch can't be measured? Other than getting rolled threads, good washers, quality lube and a "good" wrench, what do we do?

Did you ever wonder why different strength grades of fasteners are made? Why not just make them all super strong?

Each joint to be clamped becomes a problem unto itself. There are several factors that must be considered in order to fully understand how to solve the problem.

We know that torque values are mostly friction and it becomes difficult to predict torque values if we don't accurately know the friction value Mu.

Angle torque methods can be very accurate once we have defined the correct starting point. Otherwise some torque angle is used to simply take up slack and compliance.

Torque to yield technique is effective if we know the true tensile of the bolt and its measurements.

All of the above are compounded by the use of various nuts, washers, and the crushibility of the clamped medium.

There are several ways to proceed. The easiest is to obtain a fastener engineering program that will calculate and predict the torque and clamping values. We have written such a program and it is available within our Race Data Power suite of engineering spreadsheets.

Otherwise, there are alternatives.
If we obtain a block of hardened steel of appropriate thickness and drill several holes of various sizes through it, we can use it as a test bench.
Simply insert the bolt to be tested through the appropriate hole size in the block, place hardened washers under the head and nut and tighten finger tight.

Using a micrometer, measure the length of the bolt from end to end. Now begin to apply torque to the nut in gradually increasing steps. Each time a torque is applied, measure the length of the bolt. As more torque is applied to the bolt, the bolt will stretch. At some point additional torque can no longer be applied since it will only stretch the bolt. By plotting the applied torque and changes in bolt length, the elastic limit of the bolt can be determined. When no more torque can be applied without stretching the bolt, we have reached the plastic limit and the bolt will no longer return to its original length.

When the original bolt length has been stretched to 1.002 of its original length, the torque to yield point has been reached and that torque value can be used to torque bolts of the same dimension and properties. It is important to be vigilant regarding the crush of the washers or nut deformation because the clamping force will not be maintained.

Lock nuts and lock washers have been found to have little effect in the prevention of bolt loosening. Use the proper grade of Loctite or safety wire or both.

[icebluecuda]

The amount of expertise on this forum never ceases to impress. Time and again I think about writing a good reply, but I am always humbled by you guys.

[Whitewater Racer]

Considering that the bolt tightening accuracy of a torque wrench is only +- 30%, does it really matter which torque wrench is used?

I "do" motorsports, engines and racing as an avocation only. I tend to quail when folks who do this for a living make such bold, seemingly dismissive, statements. Short printed word statements over distance give me no hint as to intent. I have no way to "read" body language or pick up on visual clues. As I sit in my "places" I tend to identify the things posted as personal. My first reaction was that I had just been confronted by an intellectual "bully" and to run away!

HOWEVER, as I intellectually tried to ponder the statement and all the things, many very technical and obtained at, I suspect, great cost, that Mr Redzsus has been willing to share, I reconsidered motive and intent. I hope that he is trying to be a teacher who asks me to challenge my perceptions or asks a leading, thought provoking queston to engage me instead of just a dry transfer of fact. To try and impart knowledge by guiding the discussion along, and maybe forcing me along a tangent, so that I may be profited thereby. To make me examine where my positions come from. It makes me ask, "do I have any good, logical or factual basis for what I think of as the facts that rule my actions?" or do I just do things on an emotional level? or because that is the way it has always been done-many times with seemingly positive results---and is that good enough?

In regards to "torque wrench-does it really matter which?" I at least have some answers, now, for ME. The tools I select and use are my interface with the task. They connect my brain to the task via subtle feedback through my hands, eyes and ears. I have many different torque wrenches and kinds of torque wrenchs and use them to accomplish various things. By pulling on a torque wrench I can see, feel and listen to subtle clues about what I am applying force to. I can feel burrs, slight catches, not enough lube. Sometimes I am in positions where I can't accurately read the indicator. Other visual and auditory devices allow me to just do a smooth pull-I don't have to slow down the pull and try to read some dial or scale. The mechanical advantage of length helps me to be smooth. The balance and handle fit are important to the interface I am hoping to accomplish.

Then there is just the pure joy of using a tool. Of owning one that is designed for a specific task. This is my avocation. I can cut wire with and ax against a chunk of 2x4, but I do it better with a set of dikes and enjoy it much more. I can cook a steak with just a bonfire and a stick, but I much prefer using a barbecue. Man is a tool user and a tool maker. I like the connection that the "right" tool enables me to have with what I am doing. Finding the seeming right one is an adventure in itself.

So as far as the minutiae involved with the physics and limitations of the engineering of the parts I know too little about that to even have a clue if it really matters which is used. I can only stand on the feet of giants and hope to catch a glimpse of what they are seeing (because I can not even see their shoulders and their heads are far away seeing and seemingly understanding things far beyond my grasp.) There are just too many things to know. I hope to build on the knowing of others, but sometimes there is just the doing.

But for me, as a tool using being, yes it does matter what my interface with my task is-even if only at an emotional level, it does still matter-even if i do not have a full grasp of what is actually happening. By using the experience and guidance of others, who maybe DO know, I can hope to approximate their results. Those who do know have given me instructions, using the materials and tools they have asked us to have at hand, to accomplish the desired result. I get to pick the particular tool, of a type, that seems to work best for me. At this point in my abilites and limitations that may not be good enough to get the best results, but it is all I can do until I can make the next step.

Being ask to confront how much I do not know is always daunting and sometimes painful. But the examination can be profitable.

Thanks for the teaching moment.

[Ed-vancedEngines]

Great post Whitewater Racer,
Please consider most postings by all who have particiated in this thread and also those of Panic when you run accroiss them as not someone trying to show they know more, but instead, consider these are jewels of wisdom being shared which have been discovered though much education coupled with experience. I am not including myself in the statement just written.

I read and I marvel at the knowledge that gets freely shared here on SpeedTalk by members such as these and others here.

Youseem to be pretty sharp yourself too, and I appreciate you pitching in on the threads trying to help as well.

Ed

[Sir Yun]

to be honest i was quite surprised to read and learn about this stuff when i did..

I personally find it good to know the limitations and foundations of a measurement (that goes for any measurement. being CFM, harmonic distortion,cardiac monitoring, blood gas analyses,3d form change, whatever..).



but back to tools:

for rather large bolts ( say >100mm and such) one can use a contraption to stretch the bolt hydraulically then just tighten the nut untill it is touching the face then release.

you need about 300-500 kg force to pull most bolts to 60 %. quite a bit, but feasable

if you used some excess lenght on studs i would think that you could scale it down to work for engines.

[David Redszus]

A point not touched in earlier discussion.
In racing we often find the use of higher grade bolts than necessary. The idea is: "If a little is good, more is better, and too much is just enough."

It is often the case that a high grade bolt cannot be tightened to its elastic limit without damaging washers or clamped materials. Then the bolt works loose and fails. It was not the strength of the bolt that failed, it was the specification that was wrong.

High grade bolts used in blind holes, especially aluminum will often pull the threads out of the aluminum well before the proper bolt stretch is reached. The selection of bolt grade will depend on threaded material, in which case better is not better.

[racecar100]

Here a good infomation onTorque Wrenches

About Torque Tools


Torque, a measure of turning or twisting force, is calculated by multiplying force by distance. For example, if you applied 10 lbs. of force with a 2-ft. wrench, you would get 20 ft.-lbs. of torque; if you applied 20 lbs. of force with a 1-ft. wrench, you would also get 20 ft.-lbs. of torque.
To get the best performance from your torque tool, be sure to hold it by the handle grip and pull slowly and evenly.
Selecting the Correct Torque Range— For the most accurate performance, the maximum torque you're applying should fall near the middle of the tool's torque range. For example, if you're applying 50 ft.-lbs. of torque, it would be better to choose a wrench with a range of 5 to 100 ft.-lbs., rather than a range of 5 to 50 ft.-lbs.
Accuracy— Accuracy is usually given for 20-100% of a tool's torque range. For example, if the torque range is 20 to 120 in.-lbs., the accuracy statement is true for measurements between 40 and 120 in.-lbs. Below 20% of the torque range, the tool's accuracy often drops off significantly.
Manual Tools vs. Power Tools— Hand torque tools apply a specific amount of torque and, in some cases, check the amount of torque on a fastener. Power tools, such as impact wrenches and power screwdrivers, usually apply a range of torque on the fastener being tightened and are not intended for applying a specific torque.
Types of Torque Tools— Electronic tools are the most accurate. Readings can be downloaded into printers, PCs, and dataloggers. Adjustable tools let users set the torque value. Factory-set tools have the torque set at the factory. Click-style tools signal when torque setting is reached with an audible click that you feel in the grip and a momentary release. Torquing after the signal will cause overtorquing. Torque-limiting tools slip to prevent overtorquing, then won't apply torque again until reset. Flat-beam wrenches are the most accurate nonelectronic torque tools. Round-beam wrenches are the most economical torque tools. Dial tools have a circular scale for monitoring torque as it's being applied.
Certificates of Calibration— Torque tools are calibrated by the manufacturer and a certificate provides proof of calibration and the date it was completed. Shelf life does not affect the calibration of a torque tool. Common practice is to begin the calibration life at the date of purchase or first use.
Conversions— The chart below shows how to convert between some of the units used to measure torque.
Nm = Newton meters; dNm = deci Newton meters; cNm = centi Newton meters.

Converting Multiply
From To By

in.-lbs. in.-oz. 16
in.-lbs. ft.-lbs. 0.08333
in.-lbs. cm-kg 1.1519
in.-lbs. m-kg 0.011519
in.-lbs. Nm 0.113
in.-lbs. dNm 1.13
ft.-lbs. cNm 11.3
ft.-lbs. m-kg 0.1382
ft.-lbs. Nm 1.356
Nm dNm 10
Nm cm-kg 10.2
Nm m-kg 0.102
in.-oz. in.-lbs. 0.0625
ft.-lbs. in.-lbs. 12
cm-kg in.-lbs. 0.8681
m-kg in.-lbs. 86.81
Nm in.-lbs. 8.85
dNm in.-lbs. 0.885
cNm in-lbs. 0.0885
m-kg ft.-lbs. 7.236
Nm ft.-lbs. 0.7376
dNm Nm 0.10
cm-kg Nm 0.09807
m-kg Nm 9.807

Premium Electronic Torque Wrenches


Accurate and easy to use, these steel wrenches are ideal for auditing and high-production applications. They store up to 4000 torque values and recall up to 999 measurements in order of operation. Wrenches have a large, easy-to-read LCD that's selectable for track display (shows values as they're measured) or peak display (shows highest value). When displaying a measurement, wrenches show their sequence number and total number of stored values. You can set the desired torque along with high and low tolerance limits; lights and audible alarm signal when lower limit is met or upper limit is exceeded. Accuracy is ±1% of torque reading for 20-100% of torque range (for both clockwise and counterclockwise use). Download values using an RS-232 cable (sold separately below). Wrenches use a 9-volt battery (included), and each has a plastic case.
Note: Furnished with certificate of calibration traceable to NIST.
Square Default Scale

Drive Torque Range Graduations Selectable for Other Scales‡ O'all Lg. Each

in.-lbs.
1/4" 5 to 50 in.-lbs. 0.01 in.-lbs. ft.-lbs., Nm, dNm, cm-kg, m-kg 13.5" 8545A21 $880.82

3/8" 25 to 250 in.-lbs. 0.10 in.-lbs. ft.-lbs., Nm, dNm, cm-kg, m-kg 14.9" 8545A22 880.82

ft.-lbs.
3/8" 5 to 50 ft.-lbs. 0.01 ft.-lbs. in.-lbs., Nm, dNm, cm-kg, m-kg 14.9" 8545A23 880.82

1/2" 25 to 250 ft.-lbs. 0.10 ft.-lbs. in.-lbs., Nm, dNm, cm-kg, m-kg 21.5" 8545A11 925.32

3/4" 60 to 600 ft.-lbs. 0.20 ft.-lbs. in.-lbs., Nm, dNm, cm-kg, m-kg 46.5" 8545A31 1063.36

RS-232 to PC Cable (9-pin female) 8545A12 Each $138.47

‡ Torque ranges for other scales are direct conversions of the default scale.

Electronic Rotary Dial Torque Wrenches


Large digital display can be rotated so you can read it at any angle and has a contrast adjustment for hot and cold conditions. Colored lights and audible buzzer accompany display to let you know whether you're above, below, or within your target torque range. Wrenches have a track display, which shows values as they're measured, and a peak display, which shows the highest value. A touch of a button sets pass/fail mode for quick target tolerance settings from ±1% to ±10%. Accuracy is ±1% in both directions. Wrenches are made of steel and aluminum and are packed in a plastic case. Choose from standard 9-volt battery and rechargeable 9-volt battery with 110-volt power adapter and RS-232 output cable. Note: Furnished with a certificate of calibration traceable to NIST.
Sq. Torque Range
Graduations
O'all w/Standard Battery w/Recharg. Battery
Drive in.-lbs. ft.-lbs. Nm in.-lbs. ft.-lbs. Nm Lg. Each Each

1/4" 7.5 to 75 0.62 to 6.25 0.85 to 8.5 0.01 0.001 0.001 11" 7767A11 $386.09
7767A31 $514.55

1/4" 10 to 100 0.83 to 8.3 1.1 to 11 0.1 0.001 0.01 11" 7767A12 386.09
7767A32 514.55

3/8" 25 to 250 2.1 to 21 2.8 to 28.2 0.1 0.01 0.01 11" 7767A13 386.09
7767A33 514.55

3/8" 60 to 600 5 to 50 6.8 to 67.8 0.1 0.01 0.01 11" 7767A14 386.09
7767A34 514.55

1/2" 300 to 3000 25 to 250 34 to 340 1.0 0.1 0.1 22" 7767A15 450.23
7767A35 577.61

3/4" 720 to 7200 60 to 600 81 to 814 1.0 0.1 0.1 47" 7767A16 815.99
7767A36 932.57


Electronic Torque Wrenches



Digital display, colored lights, and audible buzzer let you know whether you're above, below, or within your target torque range. With the touch of a button, set your torque value and then a tolerance from ±1% to ±10%. Wrenches have tubular steel body; a track display, which shows values as they're measured; and a peak display, which shows the highest value. LCD has contrast adjustment for hot and cold conditions. Accuracy is ±2% in both directions. Wrenches are packed in a plastic case. Choose from standard AA batteries and rechargeable AA batteries with a 110-volt power supply and RS-232 output cable. Each is furnished with batteries and a certificate of calibration traceable to NIST.
Square Torque Range
Graduations
O'all w/ Standard Batteries w/ Recharg. Batteries
Drive in.-lbs. ft.-lbs. Nm in.-lbs. ft.-lbs. Nm Lg. Each Each

1/2" 180-1800 15 to 150 20 to 204 1 0.1 0.1 23" 8976A11 $318.73
8976A21 $450.40

1/2" 300-3000 25 to 250 34 to 340 1 0.1 0.1 23" 8976A12 318.73
8976A22 450.40


2758
n torque wrenches......

[Cammer]

Race engines can present unique threaded fastener tension problems due to special machining employed.

Machining processes changing the angular relationship between mating parts (joint face angularity) can contribute to fastener face angularity problems. If the fastener/washer/nut face contacts at an angle, tightening forces are chaotic and fastener can suffer failure.

Additionally, using improper washers can adversely effect tightening forces due to improper finishes, sizes, and hardness. Be certain to install chamfered washers properly.

Check fastener length to avoid fastener bottoming in blind holes. Fastener must have enough clearance to enable tensioning and to allow for compaction of any gasket material.

Threaded components must be clean and free of burrs. Do not use a die on bolt or stud threads and never use a tap to dress threaded holes as this can result in damaged threads.

Threaded holes should be lightly chamfered to prevent thread pulling. Make certain no burrs are left from this operation.

I like to clean threaded holes with a proper brush spun with an air pistol. I use an air gun with a hardened extension having a 45° angle tip to dislodge chips from bottoms of depth holes.

[jmarkaudio]

Here is a bit of info from my brother that does failure analysis for Siemens on steam turbine powerplants. The point of torque or stretch has less to do with the fastener, but more about the force being exerted on the fastener during operation. The idea is to load the fastener past the point of what the operating forces would exert on that fastener. As an example, the same rods in two different engines, a 350 street engine and a 350 Cup engine have different needs. Not that loading the bolts to Cup specs will necessarily hurt, but not necessary. With that said, as long as a fastener and nut or threaded hole is capable of being loaded/torqued/stretched past the point of the forces exerted on it during operation, it should never fail as well.