|11-26-2005 08:20 PM|
Added to Hotrodders Knowledge Base
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|11-20-2005 10:22 AM|
|4 Jaw Chuck||
While 2 percent is not a lot to be out, it is significant if you are torquing to above 80% tensile strength and if you consider that most torque wrenches read out up to 10% out when new (especially some of the cheap clickers). I guess thats why I like my beam style wrench, I had it calibrated when I bought it and found it out only 3 percent at 100 ft/pds. Since they don't wear and I have the indicator card from the testing/certification I trust only this wrench.
Manufacturers regularly compensate for socket extension torque loss by purchasing calibrated extensions (no wrenches to calibrate that way) but if you want to know exactly what your getting you need one of these babies.
Socket extension torque sensors
|11-19-2005 12:45 AM|
Well, I can tell you where that 2% "goes" When you twist the extension the energy is converted to heat. It warms up the extension slightly. One time is not noticeable, but do it one hundred times, and the extension will be noticeably warmer.
I will stipulate that there will be no practical difference in the torque applied to the bolt with an extension, as long as the parameters for correct wrench usage are followed.
|11-18-2005 10:37 PM|
|Bad Rat 414||
Being a mechanic Every person I ever ask for an extension gave me this...
|11-18-2005 10:26 PM|
|4 Jaw Chuck||
All that is affected by adding a socket extension is the accuracy...typically a torque wrench will display less torque the longer the socket extension is. The accuracy loss is always negative.
Torque wrench FAQ by Norbar.
Heres a snippet;
The old wives tale surrounding "extensions" and torque wrenches is related to what different people call an extension...classically an extension changes the length of the handle but most people think socket extension.
|11-18-2005 04:16 PM|
|Mr.NutCase||man this thread grows fast!|
|11-18-2005 07:30 AM|
|oldred||This whole thing has been ridiculous for more reasons than one but the worst reason is that we have been in disagreement over an error to small to matter anyway. The problem is when someone tries to correct the "error" by adding 10% or even more(NXS never said it was that much)and indeed I have seen this done. I guess that is why I take this so seriously since it usually is "corrected" by a large amount and with any kind of wrench. I have an acquittance that is an engineer with a mining equipment company and I will run my theory by him and see what he thinks.|
|11-18-2005 07:00 AM|
|11-18-2005 05:42 AM|
OK, I have been thinking about this and I may have a plausible theory(NXS will love this ) Up until now I really had not given all that much thought to this since the physics involved are obvious and this has been hashed out thousands of times over the years, BUT, Hippie seems to have uncovered a discrepancy of some sort that appears to defy logic so the question is, how? If one is using a "clicker" type wrench then there may be an explanation for the error that does indeed involve twisting. A "clicker" type wrench does not measure torque in the sense that a gauge will take a direct reading it simply releases or "fails" suddenly at a predetermined setting and once this happens it no longer "reads" anything, if you continue to pull it would not show any increase in "reading". So if using a "springy" extension and applying force at an increasing rate the extension will deflect according, that is it will deflect at an increasing rate and since the resistance at the fastener end will not "see" the full amount of force being applied to the wrench end until it reaches equilibrium it will lag behind slightly and may be the cause of the problem. Since the clicker wrench only "reads" one spot and only at the instant it senses the setting it will snap when it reaches that setting but since the resistance is lagging behind due to the increasing rate of deflection it(resistance) will not have reached an equal amount of force at that instant. This will have no effect on a gauge or beam type wrench or any other type of torque measuring device that takes a continuous reading of the resistance(torque) and in no way changes the principles involved in applying force through a shaft(an extension in this case)but it does identify a design flaw with the "clicker" type wrenches and is thus a mechanically induced error. While this is only a theory I have come up with it does seem, unless I am mistaken, to explain the discrepancy assuming Hippie was using a clicker type wrench.
Opinions on this?
|11-17-2005 07:28 PM|
I'm not going to fault your equiptment or findings,but I am in agreement with Old red that both ends of the extension should,by basic laws of physics,see the same torque.Since at 30 ft/lbs,the readings of both wrench and tester agreed,I feel that the discrepancy at 100 ft/lbs is indicative of a mechanical loss,probably due to friction in the method of support for the extension.
If a loss of torque is possible in this situation,then we would also have to accept a loss of engine torque is possible through the driveshaft and other power transmission shafts of the cars we build and drive.For example,a motor putting out 500 ft/lbs of torque at the flywheel would be losing 2% through each shaft the power was transmitted through on it's way to the differencial,then an additional 2% through the axles.We know that this is not what happens.
The 10 degree twist in the extension is indicative of additional energy in the form of a longer arc of motion needed to reach the desired torque in the system,not additional torque applied to the wrench.
If we could support the wrench end of the extension in a frictionless bearing,located so that the centerline of the extension was perfectly perpendicular to the plane of rotation of the tester,by all known laws of physics, the amount of torque exerted on the wrench will exactly equal the torque transmitted by the extension on the tester.
|11-17-2005 01:07 PM|
|oldred||Hippie, I did not take exception to your findings but I just could not help but think here we go again when you started talking about the thinner extension and flex absorbing the torque when that quite plainly is a physical impossibility. Machines are fallible due to either malfunction or input error but the laws of physics and mathematics are the laws of the universe and are inarguable. I keep asking for someone to show how an extension can have less force on one end than on the other but so far no one has made any attempt to do so. Also let's not forget that as has already been pointed out the manufacturers themselves state clearly in their manuals that this error does not exist.|
|11-17-2005 11:14 AM|
|Hippie||I'm not confusing what the test equipment tells me. 100 Ft Lbs is 100 FtLbs., 98 FtLbs is 98 FtLbs. 2 Ft Lbs. went somewhere, the machine doesn't lie. I don't have an opinion one way or another on where it went, it doesn't really matter, I saw what I saw. 2% at 100 Ft. Lbs. honestly doesn't mean squat for most of us here. You guys can keep on arguing all you want. My torque wrench is still accurate after all these years and I won't use my long 3/8" extension when I'm torquing over 30 FtLbs, that's all I really care about.|
|11-17-2005 10:30 AM|
|oldred||Hippie Why would I expect the energy to still be there? You are confusing ENERGY with FORCE. As I said earlier the total amount of energy will NOT be exerted on the fastener. The total minus what it used to twist the extension to equilibrium is what reaches the fastener but equilibrium is just that, the same amount of force on each end! The amount of force applied to a fastener is what the torque reading is, not how much energy it takes to get there and any extra energy used twisting the extension is gained by extra wrench movement using constant force(torque) . I explained this earlier the extra energy is gained from extra wrench movement and stored in the extension as static energy and will be released when the force is relaxed. You are now using the same old argument that has been tossed around for years but I bet you cannot explain why the wrench quits turning if it has less resistance on the fastener end than force applied to the wrench end. Please explain how I am wrong if I state that the force on one end HAS to be equal to the resistance on the other end or the thing would continue to turn. Simple laws of physics cannot be explained away by mechanical error.|
|11-17-2005 10:01 AM|
Like I said if it was a 1/2" extension I'm sure there wouldn't have been any difference but I could see the extension physically twist approximately 10 degrees over it's length before the wrench clicked at the 100 FtLb setting. Torque is the application of energy, where did the energy used to twist the extension come from? It had to come from the force I applied to the wrench and if the wrench "clicked off" at 100 FtLbs and some of that 100 FtLbs was being used to twist the extension why would you expect to still have 100 FtLbs at your fastener or in this case the test unit? If you use the correct strength extension then I agree there is no discernable loss, but using the lighter extension there IS loss.
|11-17-2005 09:04 AM|
|oldred||Rat. As I said It was about what what I expected Let them believe what they want or maybe we should all call up everyone from Snap-On tools to NASA and tell them they are wrong Anyway you be your own judge.|
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