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AC 43.13 is the bible, until someone can show me the math to prove it is incorrect (which I seriously doubt will happen), I will continue to go with the formula 43.13 shows with the exact length of my wrenches.
PS: I also ordered one of the wrenches, you can never have enough tools! |
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A torque is a force x an arm. If I apply a force F on a wrench L feet from a nut I will get a torque of T1: F*L=T1 If I add an extension x feet long to the wrench and apply the same force F to the wrench handle I will get a different torque T2: F*(L+x) = T2 Presumably T2 is the torque I really want. I would still measure a torque of T1 at distance L, the 'head' of the torque wrench. Think of this as the wrench setting, the wrench will 'click' (or indicate) when the torque at the head = T1 if the wrench is set to T1, but the torque at the extension will be T2. So...divide the first equation by the second: F*L/[F*(L+x)] = T1/T2 The force cancels, move the bolt torque to the other side and get: T1 = T2*L/(L+x) Or as Walt put it: Wrench setting = desired torque x wrench length / (wrench length + extension length) I have two torque wrenches, one is ~10" to grip center, the other 14". If I use a 0.8 correction for a 3" extension on both I *will* get different torques at the fastener for the same torque setting. |
Walt is correct, .8 is not a constant
Here's a simple diagram that shows the math. If the torque wrench is one foot long and the extension is 3in and installed in line with the handle then the .8 multiplier is correct if the wrench is two feet the multiplier would be .88 and if the wrench was three feet the multiplier is .92....if the extension is at an angle to the handle then the actual length E must be measured and used in the equation.
![]() Here's a good calculator: http://www.norbar.com/calculators/to...alculator.aspx P.S. the wrench is awesome and I will definitely add one tot the tool box. |
I'm just glad I already got my order in. Pretty sure Allan will be doubling the price tomorrow after all these posts :) These VAF guys are a bunch of tough customers huh? Just having a good product isn't enough any more.
Erich |
Length does matter
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Suppose I have a 12" torque wrench, with Allan's 3" extension on a bolt, and I apply 100 lbs at the tail end of the torque wrench. The torque wrench reads 1 ft * 100 lbs = 100 ft lbs, and the bolt gets 1.25 ft * 100 lbs = 125 ft lbs. So the wrench is reading 0.8 of the bolt torque. Now suppose I add a 15" cheater bar, and apply 50 lbs to the end of it. At the bolt, I've doubled the arm and halved the force, so it is seeing 2.50 ft * 50 lbs = 125 ft lbs., same as before. But the torque wrench head is now seeing, and reading, 2.25 ft * 50 lbs = 112.5 ft lbs. The wrench is reading 112.5/125 = 0.9 of the bolt torque. Which is what you get from the formula (wrench length)/(wrench length + extension), where wrench length now is 12" + 15" = 2.25ft. Length does matter. --Paul |
Length does NOT matter
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! :) |
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--Paul |
What a "torqueing" point
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!!:eek:
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*sigh*
If I have a 12" torque wrench and I apply a 80 lb force at the grip there will be a 80 ft-lb torque at the head. If I add a 3" extension (0.25 ft) straight out from the head that 80 lb will still produce 80 ft-lb at the head but it will produce 100 ft-lb at the end of the extension. That's what everyone wants. Problem is, if I use an 18" wrench, I will apply a 53.3 lb force at the handle to get 80 ft-lb at the wrench head. The torque at the bolt will be 53.3lb*(1.5+0.25 ft), or 93.3 ft-lb. Might be within tolerances, might not. It's better to know than to guess. |
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As I previously said, that nut is still going to turn the same distance to satisfy it's torque setting, wheather you apply 80 lbs or 53.3 pounds at the end of the handle, depending on length. Additional length of handle, only changes the required amount of force, that you apply to turn that nut the same amount of degrees.............as long as the original 3" remains the same. |
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HEY! I get it now, thanks to a few of the posts above. When you set the torque wrench for 100 ft lbs, by definition, you are going to have a force of 100 lbs applied 1 foot from the end of the wrench regardless of how long your wrench is, so that's where the 12 inches comes from. When you add the 3 inch extension, you are applying that 100 lbs to the close end of the extension, but more than 100 lbs to the nut at the far end of the extension. Hence the multiplier of 12/(12 + 3) = 0.8 WOO HOO! Now I can sleep. Erich |
I got an idea
Everyone agrees its a great tool. Lets go build some RV's!!!! Then we can use the tool.
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BUY!:D BUY!:D BUY!:D BUY!:D Our operators are standing buy. Thanks, Allan |
physics 101, or mechanics
Let's assume I own a torque wrench which is two feet long. If I wanted to torque a fastener to 100 Ft-lbs. I would apply 50 lbs.
50lbs. * 2 ft. = 100 ft-lbs. I buy the tool and follow the directions. I want 100 ft-lbs. of torque at the fastener, so I would set the wrench to 80 ft-lbs. (.8 * 100 = 80). That means I would apply 40 pounds of force to my end of the torque wrench, or 80 ft-lbs. to the drive end of the torque wrench. 40 lbs. * 2 ft. = 80 ft-lbs. which is the recommended torque wrench setting. Now I am ready to proceed. I attach the tool which adds 3 inches, or 1/4 foot to the system. Now my system is 2.25 feet long. (2 for the wrench + .25 for the tool) I apply the 40 pounds force to the end of the tool and the wrench clicks. I now have applied 40 lbs. * 2.25 ft. = 90 ft-lbs. |
And all this time I thought this was the Classified Section... :eek:
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I believe!
Now I am ready to proceed. I attach the tool which adds 3 inches, or 1/4 foot to the system. Now my system is 2.25 feet long. (2 for the wrench + .25 for the tool) I apply the 40 pounds force to the end of the tool and the wrench clicks. I now have applied 40 lbs. * 2.25 ft. = 90 ft-lbs.
No, because your wrench doubles your efforts first at the attach end of your torque wrench making it apply 80 lb feet there and the 3 inch extension adds 25 percent to that making 100 lbs. It really works the way Allan says!!! |
My head hurts!
Tom |
Red wrench, blue wrench...
![]() Apparently Allan is a marketing genius... |
Science vs. Religion?
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.25 is not 25 percent of 2 feet, but 25 percent of 1 foot - Science :D |
I've just had a quick look at the thread, and there seems to be quite a mix of fact and fiction here, so thanks to schristo for showing the free body diagram.
Torque is the product of a force and the perpendicular distance from that force to the point of application. So if you're applying the force at 90 degrees to the wrench then the torque measured (at the wrench) is that force times distance to the end of wrench, and the torque applied to the nut is force times distance from wrench handle to the nut. So the correction is the ratio of those two distances. Put the crowsfoot at 90 degrees and the distances are the same, so no correction, but otherwise the correction will depend on the length of wrench and length of crowsfoot offset. schristo has it right. |
Has everything to do with science, nothing about religion....
Any torque wrench is set to measure the torque where it attaches.... 6 inches long or 4 feet long matters not! It is set to measure the applied force at the attach end. So that measure is constant no matter how long Your wrench is (pun intended) the only thing that changes is the .25 foot long extension that you attach to the end of your torque wrench and that is why the correction is always the same!!
My opinion, I believe it, has not one thing to do with religion. ;) |
How to Test?
This discussion raises a question that has concerned me. I have two torque wrenches (cheap and expensive)
Is there a way that I can use wrench B to test the torque applied by wrench A? Or, can I use my wrench that's newly calibrated to test the torque applied to nuts before calibration? Or, can I use my basic torque wrench to test the torque applied when I use the device discussed in this thread to see if 0.8 really is the correct value? Or in general, do I just trust my torque wrench or is there a way I can test it? |
The length of the wrench does matter.
Have a look at the formula for calculating crows foot extension. Wrench torque = Torque Spec * (Wrench length / (Wrench length + Crows foot extension length)) You can't just multiply your desired torque by .8 and expect to get the value to place into your torque wrench. This .8 value works for a 12" / 1 foot torque wrench only. The attached image might help clear things up a bit. It assumes that you want to apply 100 FT-LB of torque to a bolt using a 3" extension using three different length torque wrenches. A one, two, and ten foot torque wrench. If you just multiply the 100FT-LB value by .8 and dial in 80 FT-LBS in your torque wrench, you can calculate the different values you will obtain. ![]() As you can see above, you won't be getting 100 FT-LBS of desired torque unless you are using a 1ft torque wrench. Stick with the formula and it will tell you what value to put into your torque wrench. |
Excellent drawing!!!
The change only happens between A and B because all the wrenches apply 80 lb ft of torque to the "B" location and B x 1.25 = 100 lb ft of torque....
I believe!.....:) |
Genius Alan - pure genius! You've managed to keep your ad at the very top of the "New Posts" for over a day! ;)
I'm putting one of your wrenches on my wish list. Now, of course, you need to make one that fits the prop bolts on our WW 151 (I think they are 5/8" heads, but I might be wrong...) - they are different from our Hartzells. |
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Adding the extension changes the location of the center point of rotation, and the head on the torque wrench is now moving in an arc, not rotation. All that said, I still think the .8 formula is correct, not too sure of the logic presented above-------Pete's or mine:eek: |
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It is slowing down a little on the posts so apparently I am going to have to stir it up with the announcement of the new coating we are thinking about changing over to. It's called "Skuzmolimide 151" and I am absolutely positive that we have many experts here with lots of experience in the use and application of this product ( any and all information can only help). Thanks, Allan:D |
bets?
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5/8" C/S Prop Bolts
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I suppose Allan is too busy filling orders to do it, but if anyone else wants to step up and show your derivation of a constant 0.8 correction factor, have at it. And while you are at it, show the derivation for the correction factor for torque wrenches that read in-lbs and newton-meters, as well as a ft-lbs one. --Paul |
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What you "feel" while pushing the handle will be different. But the nut won't be turning any more, or any less.........just because the handle is a different length. |
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But in the first case the torque at the nut is 100 lbs through a 1.25 foot arm, 125 ft lbs, for a conversion factor of 0.8. In the second case that torque at the nut is 50 lbs through a 2.25 foot arm, 112.5 ft lbs, for a conversion factor of 0.89. Quote:
Something is wrong with that logic! 1200 in-lbs just is 100 ft-lbs. Changing the labels on the torque wrench certainly shouldn't change the multiplier... Quote:
--Paul |
Another way of demonstrating.
A foot lb. is the force of 1 lb., 12" perpendicular to the pivot point. If we take 100 lbs, and set it 12" from the pivot point, then it's 100 ft. lbs torque against the pivot point. If we use a 24" or 36" wrench, we are NOT moving the 100 lbs past the 12" spot on the wrench. It remains at the 12" point. By adding a longer handle, we push with less force, to move that 100 lbs. With the addition of the 3" tool, the 12" point (which is used for the "foot" in ft/lbs. is now 15". And that's why a fraction is used. 3" & 12" remain as constants. |
Science
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To put it in perspective
My torque wrench Proto model J6014C has instructions and a formula
They use 22.57 for the handle length . If you used there formula the multiplier would be .882 (for that wrench only) If you use a 3 " extension and want to apply 80ft lbs of torque to the bolt you would set the wrench at 70.56 lbs If the wrong multiplier was used for that wrench .8 it would set at 64 lbs They would be under torqued by 9.6% if .8 was used with this wrench The best thing to do is check with the manufacture of the torque wrench used and you should have the required information. Be Safe Tim |
Easy Demo
An easy way to demo the induced torque would be to use the tool and a linear (non-settable) torque wrench. Torque a bolt with the extension, then read the required torque to loosen without it.
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The wrench will still click at the exact same spot, and the nut rotation will still stop at the exact same spot. I don't care if the handle is 3' or 30'. It's still based on that 12" (for ft/lb.) & 3". Those numbers don't change. |
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3 more inches is .25 of 12" 64 * the additional .25 = 16 64 + 16 = 80 |
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