Attn, physics majors

[jbell]

I've read torque wrenches are most accurate in their mid-range.  I don't have a 0-20 LB FT torque wrench but would a one foot socket handle pushed on by a suitable scale till it reads 10 lbs be approximately correct for 10 LB FT?  Would a two foot handle pushed to 5 lbs be the same?  I knew I should have stayed awake that day back in '64.

[Chuck in Indiana]

Assuming an accurate scale, yes.

[wrbix]

Yep, yep, and probably so.

[normzone]

Get yourself an absolutely weightless ten foot bar and put one pound on it.

https://www.physicsforums.com/threads/torque-wrench-tool-calculation.432352/

Or go buy a torque wrench...

And for extra credit, define accuracy and explain why or why not a measuring device would be most accurate in it's mid range.

[jbell]

Get yourself an absolutely weightless ten foot bar and put one pound on it.

https://www.physicsforums.com/threads/torque-wrench-tool-calculation.432352/

Or go buy a torque wrench...

And for extra credit, define accuracy and explain why or why not a measuring device would be most accurate in it's mid range.

I have four torque wrenches, beam type 0-100 Ft Lbs, clicker 0-75, clicker 0-140, and clicker 0-16 Ft lbs.  For me accuracy would be 5-10% of indicated reading, consistency is probably more important in my use, than dead on accuracy.  Lastly, price.  I'm sure there are wrenches that are within a couple percent through their entire torque range.  Again, I've read that "everyday" type wrenches are most accurate between 10 to 90 percent of their range.  Anyway, I'm needing a 14 Lb Ft reading on some clutch bolts and will be able to "verify" my torque wrench using the questioned  bar and scale method.  What could possibly go wrong?

[normzone]

From wikipedia:

Click type torque wrenches are precise when properly calibrated—however the more complex mechanism can result in loss of calibration sooner than the beam type, where there is little to no malfunction, (however the thin indicator rod can be accidentally bent out of true).

Beam type torque wrenches are impossible to use in situations where the scale cannot be directly read—and these situations are common in automotive applications. The scale on a beam type wrench is prone to parallax error, as a result of the large distance between indicator arm and scale (on some older designs).

There is also the issue of increased user error with the beam type—the torque has to be read at every use and the operator must use caution to apply loads only at the floating handle's pivot point. Dual-beam or "flat" beam versions reduce the tendency for the pointer to rub, as do low-friction pointers.

For the click type, when not in use, the force acting on the spring should be removed by setting the scale to 20% of full scale in order to maintain the spring's strength.[citation needed] Never set a micrometer style torque wrench to zero as the internal mechanism requires a small amount of tension in order to prevent tool failure due to unwarranted tip block rotation.[citation needed]

If a micrometer tool has been stored with the setting above 20% the tool should be set to 50% of full scale and exercised at least FIVE times before being used.[citation needed] In the case of the beam type, there is no strain on the component that provides the reference force except when it is in use, therefore, accuracy is inherent.[citation needed]

[Chuck in Indiana]

What could possibly go wrong?

Not a whole lot, considering how anal you're being.   

[nunzio]

THANKS.......Just when I have started to quit worrying about how accurate my Tire Gauge is!!!! 

[fotoguzzi]

THANKS.......Just when I have started to quit worrying about how accurate my Tire Gauge is!!!! 

That's FUNNY!

[Kiwi_Roy]

I've read torque wrenches are most accurate in their mid-range.  I don't have a 0-20 LB FT torque wrench but would a one foot socket handle pushed on by a suitable scale till it reads 10 lbs be approximately correct for 10 LB FT?  Would a two foot handle pushed to 5 lbs be the same?  I knew I should have stayed awake that day back in '64.

Extra points for using the correct units pound feet rather than foot pound

[Robert]

I set my clicker to what I want, then play it against my beam type, using 1/2 drive socket that just fits 1/2 drive on both ends.

Pull till clicks and watch beam.  When I am happy enough, go for it with clicker.

[acogoff]

    Been checking torque wrenches with a fish scale for years and I sure ain't no physics major. Sometimes a lot of fancy schooling is required to learn what a normal farm kid just picks up along the way.

[kevdog3019]

    Been checking torque wrenches with a fish scale for years and I sure ain't no physics major. Sometimes a lot of fancy schooling is required to learn what a normal farm kid just picks up along the way.

Nothing fishy about that!! 

[oldbike54]

 Chet , if you are reading this


                                                                       "Kansas farm boy damnit"


   

  Dusty

[Wayne Orwig]

For occasional users, I always recommend a beam type. They are cheap so you can buy a couple of ranges at a low cost. And they can set in a tool box for years, and still be accurate. Just bend the needle back to zero if needed to calibrate. Put a piece of tape and a pencil mark on the back side to use upside down.

For heavy users, it can be a PITA to see that needle. So get a clicker, or like I did, and got an electronic beeper one. I compare it to the beam every so often.

And I could find 6 tire gauges (wait, maybe 8) in my garage right now. I occasionally compare them to verify them. I had to throw away one digital one once.

[Rough Edge racing]

 There was a video posted here in the recent past showing a known bike builder discussing his bike build...And he was using a torque wrench incorrectly.......
  The wrench is only as good as the person using it...A slightly inaccurate wrench as fine so long as it's consistent.

[Wayne Orwig]

There was a video posted here in the recent past showing a known bike builder discussing his bike build...And he was using a torque wrench incorrectly.......
  The wrench is only as good as the person using it...A slightly inaccurate wrench as fine so long as it's consistent.

I worked for a long time with an otherwise good design engineer. We were having an issue with a load cell not being tightened enough in manufacturing. He kept blaming us for having bad torque wrenches, and not knowing what we were doing. We kept the wrenches calibrated and were very thorough with training. One day I was in the lab with him, as he torqued down a load cell, the wrench clicked, and he kept turning another 1/4 turn or so. I told he he had just over torqued the bolt, and he said "no way, once it clicks it can't go any higher".   
So now I knew why engineering load cells were a lot tighter then production.
Doesn't matter how good the tool is if you don't understand it. 

[not-fishing]

That's FUNNY!

Ah I found my fancy $25 motorcycle tire gauge was 25% off.  I use my Lezyne Mountain Bike pump, only a pound or two off and it makes a pound or more pressure increase every pump.

[atavar]

If you are bound and determined to jury rig it you would be better served by a spring scale that would pull rather than push.  Then multiply the reading on the scale by the length of the arm from the fulcrum point in a straight line to the point where the scale attaches.  Make sure and pull the scale as close to the direction of travel of the arm as you can, remembering that the arm travel is circular.
Exact accuracy is not as important as you might think.  The margin of error in real world torque measurements is relatively huge.  In almost all cases being in the ballpark is close enough.  In the cases of head bolts or wheel nuts precision (uniformity - so all are the same) is way more important than absolute value (accuracy) of torque.

[sib]

It's clear that what's needed here is a good refresher course on torque wrenching. I suggest:

https://www.youtube.com/watch?v=jdVR6T0cxXg

[mtiberio]

Not quite, but funny none the less...

[normzone]

I worked for a long time with an otherwise good design engineer....One day I was in the lab with him, as he torqued down a load cell, the wrench clicked, and he kept turning another 1/4 turn or so. I told he he had just over torqued the bolt, and he said "no way, once it clicks it can't go any higher".   
So now I knew why engineering load cells were a lot tighter then production.
Doesn't matter how good the tool is if you don't understand it.

Wow. Just wow. I work in QA, and herd engineers among others. They are, unfortunately, human. Training is often required. 

[Chuck in Indiana]

I have met many engineers that were educated beyond their intelligence..

[charlie b]

That's ok, we engineers have the same kinds of stories and jokes about physicists.  :)

I can't say I've never designed something that did not work well, but, everything I designed I had to operate so I had different motivation :)

[Ighani]

An alternative to using a torque wrench-for metric fasteners: tighten it till it strips, then back it out 1/4 turn. Not sure if it's the same for inch fasteners.

[charlie b]

For inch fasteners you back out 4 inches, measured at the end of whatever wrench you are using  :D

[jbell]

Not a whole lot, considering how anal you're being.   

That comes from a rather unfortunate incident many, many years ago involving a Franz Oil Filter, the woods and a bear.

[Mark_Z]

A further test would be to explain the difference between accuracy and presision.

Extra credit (my favorite conversion problem for my nursing students taking bonehead chemistry): Everyone knows that the speed of light in a vacuum is 186,000 miles per second. What is the speed of light in furlongs per fortnight?

[Kiwi_Roy]

1.799 x 10 to the power of 12

[oldbike54]

 Why would anyone need to know the speed of light in a vacuum , ... wait , will my Kirby exceed the speed of light  Where is that setting and why haven't you guys told me about this ?

  Dusty