Van's Air Force
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- Thread starter PerfTech
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Captain Avgas
Well Known Member
JMHO... this Gentleman, Allan has PAID for advertisement space on VAF. He has posted a Classified Ad, not a discussion thread. At what point do stop beating on Allan for his PAID advertising? If you like his products, buy them. If you have a question about them, call him. If I remember correctly folks getting BANNED for beating up PAID adverisers here on VAF...
Well, in the words of Doug Reeves himself, VansAirforce is "a place for people building and flying RV kitplanes to socialize, network, get inspiration and receive help from others". My best guess is that the current discussion falls firmly into the latter "helping each other" category. There are obviously many educated people on this forum who firmly believe that Allan is providing incorrect, and potentially unsafe, information and they subsequently feel an obligation to point out that fact to others. And in my opinion they would be morally bankrupt if they did not do so.
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Wow
I can not wait to see Allan's video example. He is completely correct and knows it. For many it will be very educational
The biggest problem is the poor formula for torque extensions. Allan's example in post #22 is no exeption.
When converting, 12 inches is always used with ft/lb and 1 inch is always used with in/lb for "L" in the equation. This applies to all types of torque wrenches when using the indicated reading on the wrench.
If the handle length is used the amount of neccessary force applied to the handle is calculated and would have to converted back to ft/lb's.
George
RV8
I can not wait to see Allan's video example. He is completely correct and knows it. For many it will be very educational
The biggest problem is the poor formula for torque extensions. Allan's example in post #22 is no exeption.
When converting, 12 inches is always used with ft/lb and 1 inch is always used with in/lb for "L" in the equation. This applies to all types of torque wrenches when using the indicated reading on the wrench.
If the handle length is used the amount of neccessary force applied to the handle is calculated and would have to converted back to ft/lb's.
George
RV8
Spanner in the works
So, I have 2 foot long torque wrench but instead of pulling it at the handle, I decide to pull it in the middle 1 foot down its length.......will this alter the setting required.
It seems to me that a lot of intelligent people are getting themselves tied in knots trying to understand whats going on here.
For Allans extension spanner to provide 100lbs/ft at the nut, it requires a certain pressure applied at the attachment point to the torque wrench. The amount of pressure will not change no matter how long the torque wrench is. What will vary is the amount of pressure applied by the operator to the torque wrench handle, and the amount of stroke required.
Think about your joy sticks and the effect of varying their length. The loads on the control surfaces dont change, but the load you have to apply to the stick does vary, and the amount you have to move it.
Your mileage and stick length may vary
So, I have 2 foot long torque wrench but instead of pulling it at the handle, I decide to pull it in the middle 1 foot down its length.......will this alter the setting required.
It seems to me that a lot of intelligent people are getting themselves tied in knots trying to understand whats going on here.
For Allans extension spanner to provide 100lbs/ft at the nut, it requires a certain pressure applied at the attachment point to the torque wrench. The amount of pressure will not change no matter how long the torque wrench is. What will vary is the amount of pressure applied by the operator to the torque wrench handle, and the amount of stroke required.
Think about your joy sticks and the effect of varying their length. The loads on the control surfaces dont change, but the load you have to apply to the stick does vary, and the amount you have to move it.
Your mileage and stick length may vary
380mxc
Member
Ac 43.13-1B
Can someone show me how the formula in AC43.13-B figure 7-2 for the torque wrench adapter is wrong.
It dissagrees with using .8 as a constant.
My torque wench manufacturer says the handle length is 22.57 inches and my extension is 3".
If the formula from AC43 is used, 70.61lbs shoud be my setting on the wrench
If the .8 constant is used, 64lbs should be my setting on the wrench.
Thanks for your help
Tim
Can someone show me how the formula in AC43.13-B figure 7-2 for the torque wrench adapter is wrong.
It dissagrees with using .8 as a constant.
My torque wench manufacturer says the handle length is 22.57 inches and my extension is 3".
If the formula from AC43 is used, 70.61lbs shoud be my setting on the wrench
If the .8 constant is used, 64lbs should be my setting on the wrench.
Thanks for your help
Tim
Bob Kuykendall
Well Known Member
It depends on the type of torque wrench being used. For a clicker or dial indicator type, the indicator or click will be accurate, since the measurement is entirely internal to the wrench. However, you will have to apply twice the force at the 1-foot mark as you would at the handle to achieve the same torque at the nut.
Edit add: It turns out I might be wrong about part of this. A video linked from a later post seems to demonstrate that applying force to the middle of a torque wrench will disrupt its accuracy. However, it does not sway my conviction about the invalidity of the "0.8 correction factor."
For a beam-style wrench, the indication will not be accurate if you apply force at any place except at the handle. The accuracy of the indication scale near the handle depends on the beam being loaded in simple bending by a force applied at the center of the handle. Most such wrenches have a rocking pivot built into the handle that ensures that the force is applied to the beam only at the correct point.
It seems to me that a lot of people are putting a lot of effort into clarifying what is going on because it is a safety of flight issue with potentially deadly consequences.
Statements like that tend to be the places where this discussion goes off the rails. We are not talking about pressure here, we are talking about forces and torques. Those three things are very different and have very specific meanings. We have to keep our terms straight in order to discuss this intelligently.
A force is, well, a force, aplied at a point. Forces are measured in units like pounds or Newtons. A pressure is a force applied over an area. The air in your tires applies a pressure something like 30 lbs per square inch to the inner surface of the tire.
A torque is the result of a force applied at some distance from an axis that causes bending or rotation. Torques are measured in in-lbs, ft-lbs, Newton-meters, and things like that. An inch-pound is the torque that results from a force of one pound applied at a distance of one inch from the axis. A Newton-meter is a force of one newton (there are nominally 9.8 newtons per kilogram) applied at a distance of one meter from the axis.
You might ask, if the Metric system is decimal, why are there 9.8 Newtons per kilogram, and not ten? It's because the Newton is a measurement of force that is independent of the 9.8 meter-per-second^2 acceleration of gravity. But that might be the start of a discussion for a different day.
Thanks, Bob K.
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Bob Kuykendall
Well Known Member
Nice, thanks for posting that! It is a good description of what is going on, and the calculator makes it easy to test different combinations of wrench length, extension length, and torque value.
Thanks, Bob K.
Totally Agree
Bob
I totally agree about the potential dire consequences, and forgive my poor choice of words, should have said force.
I think the point I was trying to make is that there are a lot of opinions and calculations going on here which I suspect would cause more confusion. Also trying to put a light side on the thread.
Bottom line is if you search the web there is usually a calculator set up to do the mathematics for you.
Bob
I totally agree about the potential dire consequences, and forgive my poor choice of words, should have said force.
I think the point I was trying to make is that there are a lot of opinions and calculations going on here which I suspect would cause more confusion. Also trying to put a light side on the thread.
Bottom line is if you search the web there is usually a calculator set up to do the mathematics for you.
Bob Kuykendall
Well Known Member
Steve, my apologies for the brusque tone. The page you posted earlier, with the example and the calculator helps a lot to clarify what is going on here.
Thanks, Bob K.
Here is another one
Bob
To be fair I was being a little naughty, in an attempt to lighten the tone. I was not actually expecting an answer, so no offense taken
Here is a better calculator which allows you to work out the torque setting when the crows foot is at different angles. The interesting point is that when it is at 90 degrees, you set the actual torque required on the nut.
http://www.cncexpo.com/TorqueAdapter.aspx
Perhaps I am getting lazy, although I could understand the maths if I dug into it, I don't need to.......... the web is fantastic!
Bob
To be fair I was being a little naughty, in an attempt to lighten the tone. I was not actually expecting an answer, so no offense taken
Here is a better calculator which allows you to work out the torque setting when the crows foot is at different angles. The interesting point is that when it is at 90 degrees, you set the actual torque required on the nut.
http://www.cncexpo.com/TorqueAdapter.aspx
Perhaps I am getting lazy, although I could understand the maths if I dug into it, I don't need to.......... the web is fantastic!
Steve - Bob,
Please watch this video. It shows that for a clicker wrench you should not use it by grasping it in the middle. It will alter the setting required.
http://www.youtube.com/watch?v=_1LZk0jnQrA&context=C325b44eADOEgsToPDskIx5vlwJgRu2bTi566Hn1Lf
L.Adamson
Well Known Member
After reviewing this video several times on a big screen, I can see that the movement of the arm, of "dial" torque wrench............is much more, when the click wrench is grasped at half it's length. It would seem, that this could effect the measurement we're looking for. Just an observation, as I have no facts.
Thanks
Chris
Thanks for posting this. In a previous life I served an engineering apprenticeship and would never hold the clicker or beam wrench in the middle. I hope what I said does not give anyone the idea that it OK to do this. As the video shows holding the wrench in the middle increases the force applied on the nut.
Your video should show the folly of this. Actually, we used to use a type of crows foot to tighten cylinder heads which put the drive directly over the bolt being tightened, so no correction factor was required for varying length torque wrenches.
All this discussion reminds me of a TV show many years ago called Tomorrows World. The topic was tightening nuts and bolts and the elastic limit of bolts. From memory ( which is getting a bit dodgy), the best way of ensuring the bolt was tightened to its maximum without exceeding the elastic limit was a very accurate measurement of the bolt length/stretch. The second best was a skilled craftsmans hands, and they showed that some people were almost as accurate by feel. The torque wrench came in third.
The tendency for the mere mortals is to over tighten, so a torque wrench is essential.
Chris
Thanks for posting this. In a previous life I served an engineering apprenticeship and would never hold the clicker or beam wrench in the middle. I hope what I said does not give anyone the idea that it OK to do this. As the video shows holding the wrench in the middle increases the force applied on the nut.
Your video should show the folly of this. Actually, we used to use a type of crows foot to tighten cylinder heads which put the drive directly over the bolt being tightened, so no correction factor was required for varying length torque wrenches.
All this discussion reminds me of a TV show many years ago called Tomorrows World. The topic was tightening nuts and bolts and the elastic limit of bolts. From memory ( which is getting a bit dodgy), the best way of ensuring the bolt was tightened to its maximum without exceeding the elastic limit was a very accurate measurement of the bolt length/stretch. The second best was a skilled craftsmans hands, and they showed that some people were almost as accurate by feel. The torque wrench came in third.
The tendency for the mere mortals is to over tighten, so a torque wrench is essential.
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Bob Kuykendall
Well Known Member
Well
After research it seems all is not as simple as first thought. The common calculations using torque wrench arm length in calculations appear to be correct and my simple math and Allan's .8 conversion are incorrect.
There was the exact same scenario questioned on the physics forum. http://www.physicsforums.com/showthread.php?t=432352&page=2
Allan's explanation/video should be very interesting.
George
After research it seems all is not as simple as first thought. The common calculations using torque wrench arm length in calculations appear to be correct and my simple math and Allan's .8 conversion are incorrect.
There was the exact same scenario questioned on the physics forum. http://www.physicsforums.com/showthread.php?t=432352&page=2
Allan's explanation/video should be very interesting.
George
Bob Kuykendall
Well Known Member
Yes, Allan is correct for that one specific case of the 12" torque wrench. He is incorrect for all other lengths. It similar to the broken clock being right twice a day.
Thanks, Bob K.
sstellarv10
Well Known Member
Wow Allan, you couldn't have asked for any better advertising than this thread has created.
Captain Avgas
Well Known Member
Wow Allan, you couldn't have asked for any better advertising than this thread has created.
That might be true, but only if you believe that "all exposure is good exposure".
BillL
Well Known Member
Scary
This thread has been kind of scary with all kinds of directions of the arguments and lack of mathematical rigor. Even that youtube video drove incorrect conclusions due to the poor conditions of the test. Care was not taken to ensure torque alone was transferred from the click wrench to the dial. You could see that from the bending.
I like the tool and knowing the offset is 3 inches is just fine when properly used for the torque wrench length one chooses.
The fundamental engineering principles to address this whole situation, should one want to pursue, is the concept of the free body diagram in statics. Sum forces in the x and y direction and moments about a common point.
Allen, considering all the confusion resulting here you should correct your video (re the .8 factor) so that the less informed will not end up with improper torque. All torque wrenches don't have a 12 inch moment arm, nor their users the benefit of the talent on VAF Forums.
This thread has been kind of scary with all kinds of directions of the arguments and lack of mathematical rigor. Even that youtube video drove incorrect conclusions due to the poor conditions of the test. Care was not taken to ensure torque alone was transferred from the click wrench to the dial. You could see that from the bending.
I like the tool and knowing the offset is 3 inches is just fine when properly used for the torque wrench length one chooses.
The fundamental engineering principles to address this whole situation, should one want to pursue, is the concept of the free body diagram in statics. Sum forces in the x and y direction and moments about a common point.
Allen, considering all the confusion resulting here you should correct your video (re the .8 factor) so that the less informed will not end up with improper torque. All torque wrenches don't have a 12 inch moment arm, nor their users the benefit of the talent on VAF Forums.
Bob Kuykendall
Well Known Member
Exactly. All the time I've been contributing to this thread I was thinking of the DecorMyEyes debacle.
Thanks, Bob K.
Bob Kuykendall
Well Known Member
Just in case we've forgotten what we're arguing about, I thought I'd quote this back here at the end of the thread, closer to where the latest discussion is.
IT's Saturday night... it's enough torture for the week.
A few who are in the know are conspicuously absent. :-(
A few who are in the know are conspicuously absent. :-(
The reason length doesn't matter is that the torque wrench is indicating the torque on the nut, and not the force on the end of the wrench.
A wrench handle can be any length, and if the torque reading is calibrated at the nut end of the wrench, it will tell you the torque on the nut, which is what you want.
So, wrench #1 is 10 feet long, with a dial that indicates ft-lbs (or more correctly lb-ft) at the NUT. if you want 100 pounds of torque, you would apply a force of 10 lbs at the handle, and the dial would read 100. (10 feet X 10 lbs = 100 ft-lbs)
Wrench #2 is 1 foot long, with a dial that reads torque at the NUT. If you want 100 lbs of torque, you would apply a force of 100 lbs at the HANDLE, and the dial would read 100. (1 foot X 100 lbs = 100 ft-lbs)
You guys are confusing the nut torque with the force needed at the handle.
All torque wrenches read TORQUE AT THE NUT, not force on the end of the handle.
That's why the length of the handle doesn't matter for torque wrenches.
Taking all bets!
I will try this one more time. Forget the length of your wrench, Forget cheater bars and everything else. If you have a torque wrench that you currently use to torque things in foot lbs. and you want to torque a bolt to 100 foot lb. you set your wrench or reed your gauge at 100. If you use our prop wrench with your torque wrench and want 100 foot lbs. you set or read your torque wrench to 80 foot lbs. You do not need to do any math or calculations of any kind. We have done that for you. Allan
And here we are back at what Allan said right at the beginning. He has done the math for us and in order to achieve the desired torque on the nut one would have to set the wrench at .8 of whatever ft-lbs you require. The reason is that the point of torque on the nut has been moved by 3'' which will always remain the same as long as you are using Allan's prop wrench. In other words the torque wrench will "click" at the correct torque setting regardless of the length of the handle. If however, you were using an ordinary flat or ring spanner and extended the handle it would be a very different story!!
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BillL
Well Known Member
Still Missing the math . .
Sorry Bob, but although I don't know how to properly use quotes on this site, but I can do simple math and this quote below is simply wrong.
Here is the simple math - My torque wrench is 16 inches to the center. So that means put a force of 75 pounds of force to yield 100 ft-lbf. For the math that is 16*75/12=100. Now lets add the 3 inches. Now the moment arm is 19 inches (16+3=19) and the wrench is still set to 100 and I still pull with 75 pounds. Simple math: 19*75/12=118.75 ft-lb. Hmmm . . . . simply not .8. This "factor" is .8421. So the math does work and the statement below is not factual.
"Originally Posted by PerfTech
All foot lb. torque wrenches are the same regardless of handle overall length. The overall length only effects how hard you need to pull on it. on a foot lb. torque wrench the .8 multiplier is exactly and always the number. It is not rounded off and it never changes as long as the crows foot or our tool is 3" and in installed straight. If you install it on the torque wrench at 90 degrees the multiplier is 0, at a 45 degree angle it is .9. This is simple math and does not change."
Sorry Bob, but although I don't know how to properly use quotes on this site, but I can do simple math and this quote below is simply wrong.
Here is the simple math - My torque wrench is 16 inches to the center. So that means put a force of 75 pounds of force to yield 100 ft-lbf. For the math that is 16*75/12=100. Now lets add the 3 inches. Now the moment arm is 19 inches (16+3=19) and the wrench is still set to 100 and I still pull with 75 pounds. Simple math: 19*75/12=118.75 ft-lb. Hmmm . . . . simply not .8. This "factor" is .8421. So the math does work and the statement below is not factual.
"Originally Posted by PerfTech
All foot lb. torque wrenches are the same regardless of handle overall length. The overall length only effects how hard you need to pull on it. on a foot lb. torque wrench the .8 multiplier is exactly and always the number. It is not rounded off and it never changes as long as the crows foot or our tool is 3" and in installed straight. If you install it on the torque wrench at 90 degrees the multiplier is 0, at a 45 degree angle it is .9. This is simple math and does not change."
Bob Kuykendall
Well Known Member
Bill, I agree with you. Allan's math is still invalid. But not everyone here believes that yet, and some have lost track of what the central point of this thread is.
Thanks, Bob K.
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Bill, I agree with you also. The .8 is not a constant and I think Allan should make that correction.
I also agree with you the the test conditions in the youtube video I made were not ideal, but they were good enough to show that the length of the wrench matters. The "bending" you see in the video is not actually bending, it is my welding table that the vise is attached to rocking. It looks like the dial wrench handle is bending because of the ultra wide angle lens on the camera. I can assure you it looks much worse in the video than in person.
I think that Bob and I and others have done way more than should have been necessary to try and explain through mathematical rigor, free body diagrams, moment diagrams and videos why an established and published equation for using a crows foot is correct.
Once again I ask the disbelievers what they would have done if Allan had not given any multiplication factor?
Torque wrenches,used properly, especially dial and beam ones, are perfectly good at setting bolt/nut torque. What they're not good at is setting bolt pre-load. If you have a fastener that needs to be at a certain pre-load, you'll want to measure the stretch in the bolt with either a micrometer, a strain gage or a piezeoelectric crystal crystal (think time of flight of a sound wave).
rocketman1988
Well Known Member
Wow, with all this discussion, I'm almost afraid to fly my primary airplane because it's got so many bolts that were probably torqued incorrectly...
Guess I'll have to call Boeing to make sure...
Guess I'll have to call Boeing to make sure...
Av8torTom
Well Known Member
Well....
I've been following this thread for a couple of days now and have gone back and forth on a few concepts, but this I KNOW is COMPLETELY wrong...
I've been following this thread for a couple of days now and have gone back and forth on a few concepts, but this I KNOW is COMPLETELY wrong...
The beam style wrench also needs to be held by the handle and it must be neutral.
Av8torTom
Well Known Member
Roll over Archimedes...
This is bizarre. At the risk of beating this to death, when a beam-style wrench says 25 inch lbs, it's 25 inch lbs - no more no less, and it makes NO difference where you hold the wrench. The only difference is that holding the wrench halfway down the handle will require exactly twice the force BY THE OPERATOR as when held at the end of the handle to achieve the same torque. The formula is simple Torque = Force X Distance X sine of the angle of the force on the handle (the sine of 90 deg is 1 so we usually disregard this). If the operator needs to exert 2 lbs of force at the end of the handle to achieve a given torque setting, then s/he will get the exact same torque when 4 lbs is applied half-way down the wrench handle...(2XL = 4Xhalf L) but the torque is WHATEVER the wrench reads. i.e., it has no idea where it's being held.
The torque in the illustration is the same at position A and B = 20 ft lbs.
I have NO idea what's going on with that clicker wrench in the video - that's just weird... but important to know.
This is bizarre. At the risk of beating this to death, when a beam-style wrench says 25 inch lbs, it's 25 inch lbs - no more no less, and it makes NO difference where you hold the wrench. The only difference is that holding the wrench halfway down the handle will require exactly twice the force BY THE OPERATOR as when held at the end of the handle to achieve the same torque. The formula is simple Torque = Force X Distance X sine of the angle of the force on the handle (the sine of 90 deg is 1 so we usually disregard this). If the operator needs to exert 2 lbs of force at the end of the handle to achieve a given torque setting, then s/he will get the exact same torque when 4 lbs is applied half-way down the wrench handle...(2XL = 4Xhalf L) but the torque is WHATEVER the wrench reads. i.e., it has no idea where it's being held.
The torque in the illustration is the same at position A and B = 20 ft lbs.
I have NO idea what's going on with that clicker wrench in the video - that's just weird... but important to know.
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You are absolutely correct. Torque coarsely measures the preload of a bolt thru the relationship: Torque = .2*Preload*Bolt Diameter. This relationship has many variables such as lubrication, surface finish of the threads, etc. In a situation where preload is critical, such as connecting rod bolts, bolt stretch or strain should be measured.
Here's a couple of pictures of an extensometer that I designed for work that measures the strain in a 20 foot long 3" diameter tie rod used in a nuclear reactor. The total strain over the three foot length of the tool was only .003" at the preload that was required. The tool also had to be installed remotely 60 feet underwater. It's a fun job sometimes.
BillL
Well Known Member
Click Wrench Innards
http://www.tegger.com/hondafaq/torque_wrench/index.html
Here is an exposed view of the insides of a click wrench. It may help to see how it works.
Cool discussion on bolt stretch. Caterpillar large engines for locomotives use hydraulic pullers to pull all 4 head studs to a fixed force/extension/strain, then a cylindrical "nut" is moved in place with a small dowel rod and simply snugged by hand force. Connecting rod bolts use stretch to "set" pre-load.
Nearly all our critical fasteners that are torqued, are lubricated to ensure known thread friction, and use relatively hard washers as well for the same reason. It is interesting that we don't do this in aero, I can only think that class 5 aero fasteners are not stressed that high to avoid fatigue failures that result in fastener separation. It is more desirable to just come loose while remaining intact.
Hope this is not too much off topic.
http://www.tegger.com/hondafaq/torque_wrench/index.html
Here is an exposed view of the insides of a click wrench. It may help to see how it works.
Cool discussion on bolt stretch. Caterpillar large engines for locomotives use hydraulic pullers to pull all 4 head studs to a fixed force/extension/strain, then a cylindrical "nut" is moved in place with a small dowel rod and simply snugged by hand force. Connecting rod bolts use stretch to "set" pre-load.
Nearly all our critical fasteners that are torqued, are lubricated to ensure known thread friction, and use relatively hard washers as well for the same reason. It is interesting that we don't do this in aero, I can only think that class 5 aero fasteners are not stressed that high to avoid fatigue failures that result in fastener separation. It is more desirable to just come loose while remaining intact.
Hope this is not too much off topic.
This is bizarre. At the risk of beating this to death, when a beam-style wrench says 25 inch lbs, it's 25 inch lbs - no more no less, and it makes NO difference where you hold the wrench. The only difference is that holding the wrench halfway down the handle will require exactly twice the force BY THE OPERATOR as when held at the end of the handle to achieve the same torque. The formula is simple Torque = Force X Distance X sine of the angle of the force on the handle (the sine of 90 deg is 1 so we usually disregard this). If the operator needs to exert 2 lbs of force at the end of the handle to achieve a given torque setting, then s/he will get the exact same torque when 4 lbs is applied half-way down the wrench handle...(2XL = 4Xhalf L) but the torque is WHATEVER the wrench reads. i.e., it has no idea where it's being held.
The torque in the illustration is the same at position A and B = 20 ft lbs.
I have NO idea what's going on with that clicker wrench in the video - that's just weird... but important to know.
Tom,
A beam style wrench is measuring the torque by indicating the deflection in the beam. Therefore where you apply the load is critical.
For the clicker, intuitively you would think it doesn't matter where you hold the wrench because of the internal spring and pawl mechanism. But there are internal frictional forces (like the point where the wrench "breaks") that increase if you move your hand closer to the head of the tool because you have to apply more force for the same torque. I believe this is why there is a relatively large error shown in the video. If I add an extension to the handle the wrench breaks at a smaller torque than it is set to but the error is much less. On the request of BillL, I reran the test in the video holding the dial torque wrench at exactly the area on the handle marked as the active area by holding the wrench in a collet on my lathe. This was very stable and I got the exact same results as shown in the video.
Mike S
Senior Curmudgeon
Correct, the reading of the torque generated is due to the scale moving under the fixed pointer.
The scale is calibrated to the bend of the entire length of the rod/beam, not the half length ETC.
This is why good beam torque wrenches have a rocking handle, it make the applied force always impact the same location on the beam.
Tom, I would agree with your drawing, and statement for a click type, but not a beam.
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Av8torTom
Well Known Member
Very Interesting
I see your points about the beam bending.
I just went into the shop and using a spring operated fish scale it took exactly twice as much "pull" to reach 25 inch lbs in the middle of the wrench as it did at the end of the wrench.
I think what we're arguing here are the idiosyncrasies of the measuring device and not the physics of torque. Nevertheless - important stuff to understand.
I see your points about the beam bending.
I just went into the shop and using a spring operated fish scale it took exactly twice as much "pull" to reach 25 inch lbs in the middle of the wrench as it did at the end of the wrench.
I think what we're arguing here are the idiosyncrasies of the measuring device and not the physics of torque. Nevertheless - important stuff to understand.
Let me just say, there are three reasons for the click torque wrench to get shorter when you set the scale to a higher torque value.
My 1/2" drive gets 1.5" shorter at 100 ft lbs. So it may be a 12" torque wrench, but set at 80 ft lbs, it is only a 11" torque wrench!!
I hope this does not cause an argument.....................
As you can see, I will measure length and do the math like EVERY torque wrench manufacturer (that I have researched) explains when adding extensions.
Waiting for the video..........
My 1/2" drive gets 1.5" shorter at 100 ft lbs. So it may be a 12" torque wrench, but set at 80 ft lbs, it is only a 11" torque wrench!!
I hope this does not cause an argument.....................
As you can see, I will measure length and do the math like EVERY torque wrench manufacturer (that I have researched) explains when adding extensions.
Waiting for the video..........
A thought experiment
Allan's wrench is 3" in length. In order to get 100 ft/lbs of torque at the nut, a force of 400 lbs must be applied to the wrench. 400 lbs X .25 feet = 100 ft/lbs.
Now, instead of using a torque wrench to tighten the nut, use a breaker bar. If the breaker bar was 9" in length (.75 ft), then the total length of the breaker bar and Allan's (now famous) wrench would be one foot, and the force needed at the end of the breaker bar would be 100 lbs. The breaker bar is applying torque to the square hole on Allan's wrench, but we are not able to read it.
Here's the key part: The breaker bar is not only applying torque at the square hole, it is doing something much more important: it is applying the 400 lbs of force needed to get the 100 ft/lbs at the nut.
Now substitute a torque wrench for the breaker bar, and now you can read the torque at the square hole. But that's not the only force, you are still applying a side force at the hole that the torque wrench doesn't measure.
That's why the formula's that include length of the torque wrench do matter. I think that if Allan produces a video, he may have to change the instructions on use of his wrench.
Suited up......................
Sorry Allan, I've switched to the other camp...
Allan's wrench is 3" in length. In order to get 100 ft/lbs of torque at the nut, a force of 400 lbs must be applied to the wrench. 400 lbs X .25 feet = 100 ft/lbs.
Now, instead of using a torque wrench to tighten the nut, use a breaker bar. If the breaker bar was 9" in length (.75 ft), then the total length of the breaker bar and Allan's (now famous) wrench would be one foot, and the force needed at the end of the breaker bar would be 100 lbs. The breaker bar is applying torque to the square hole on Allan's wrench, but we are not able to read it.
Here's the key part: The breaker bar is not only applying torque at the square hole, it is doing something much more important: it is applying the 400 lbs of force needed to get the 100 ft/lbs at the nut.
Now substitute a torque wrench for the breaker bar, and now you can read the torque at the square hole. But that's not the only force, you are still applying a side force at the hole that the torque wrench doesn't measure.
That's why the formula's that include length of the torque wrench do matter. I think that if Allan produces a video, he may have to change the instructions on use of his wrench.
Suited up......................
Sorry Allan, I've switched to the other camp...
Birkelbach
Well Known Member
I was unable to find the tools that I needed to make my video this weekend. Sorry 'bout that, but my wrench is 13" long so it wouldn't show the differences.
The ironic thing about the discussion is that we've shown that the clicker type wrenches care about where the force is applied to the handle and if you stop and think about it carefully the reason is that a clicker type wrench is actually measuring the torque at a slightly offset distance from the center of the nut. So internally it's a torque wrench with a small fixed length extension.
The question really comes down to this... The equation for calculating torque with an extension has been quite thoroughly documented on this forum. The equation has a variable that represents the length of the torque wrench. The argument to support the original claim is that we can eliminate this variable by the choice of our measuring units. I submit that this idea would get you a failing grade on any high school physics test.
The ironic thing about the discussion is that we've shown that the clicker type wrenches care about where the force is applied to the handle and if you stop and think about it carefully the reason is that a clicker type wrench is actually measuring the torque at a slightly offset distance from the center of the nut. So internally it's a torque wrench with a small fixed length extension.
The question really comes down to this... The equation for calculating torque with an extension has been quite thoroughly documented on this forum. The equation has a variable that represents the length of the torque wrench. The argument to support the original claim is that we can eliminate this variable by the choice of our measuring units. I submit that this idea would get you a failing grade on any high school physics test.
erich weaver
Well Known Member
Hard to argue with that. And while I have found myself swayed toward the '0.8 multiplier as a constant' by a few conceptual arguments made during the course of this thread, I havent seen any published documentation presented that supports that position. Nonetheless, I eagerly await the videos that will demonstrate beyond question how the world really works.
erich
Having followed this thread and really enjoying all the "entertaining" explanations, I can hardly wait for the theoretical discussion and explanations of and for a "ratcheting" open-end wrench!! Oughta be good!
I made my first open end ratcheting wrench over 20 years ago to allow the quick adjustment of gas orifices. The wrench requires a profile of four of the six sides of the nut-bolt. With one beak ground down with just a small shoulder left, the wrench can now jump the flat to grab the next without lifting the wrench completely off of the nut-bolt. It is for quick travel only, not for final torquing.
Lonnie, do you think that will start it?
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