Part of my job is calibrating torque wrenches. The majority of the clicker types are rated at ±4% of setting between 20% and 100% of full scale. Below 20% of full scale they are generally so inaccurate as to be unusable. Some of the more expensive wrenches are 3% of full scale (Proto for example). For the price, the Craftsmen clicker type is a great value. They generally check good and are not too difficult to adjust. On the other end of the spectrum I seldom find a "Westward" brand wrench within tolerance. The digital wrenches are the most accurate, but unless you have an extremely sensitive touch most of that accuracy is unusable. The dial type torque wrenches are anywhere between 2% of setting to 4% of setting. They are probably the most difficult type to use (hard to read the dial and turn the wrench simultaneously). They are most useful for checking something that is already torqued. To get the best accuracy on the clicker type wrench run them up to full scale and exercise them a few times. Then, return to the bottom of the scale and run them up to the torque setting you need. When finished always return the wrench to the lowest setting to preserve the spring.
Torque Wrench Primer
- Thread starter redbone3
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Got two Proto torque wrenches. Love them both.
Originally Posted By: redbone3
The digital wrenches are the most accurate, but unless you have an extremely sensitive touch most of that accuracy is unusable.
I don't quite follow that. If digital torque wrenches preserve their accuracy over considerable use, that is a good thing, isn't it? What does "sensitive touch" have to do with the accuracy of a torque wrench?
The digital wrenches are the most accurate, but unless you have an extremely sensitive touch most of that accuracy is unusable.
I don't quite follow that. If digital torque wrenches preserve their accuracy over considerable use, that is a good thing, isn't it? What does "sensitive touch" have to do with the accuracy of a torque wrench?
When I check a digital wrench I check it against a calibrator that reads out the peak torque applied during the test. It requires a very sensitive touch to not overshoot the torque you are going for. You would never see that in use, but during calibration you can read out the overshoot on the calibrator. So, you may think you have a very accurate torque when you actually overshot it considerably. In answer to the Harbor Freight question; For the price they are good. They get better with age. When new they are not very accurate, showing a lot of variation between readings. After use they generally settle down.
How does the clicker type adjust?
I have a couple of older (30 to 35 yo) Craftsman, and a few Harbor Freight. I check them against a beam one which is not used for anything but checking the torque wrenches.
I have a couple of older (30 to 35 yo) Craftsman, and a few Harbor Freight. I check them against a beam one which is not used for anything but checking the torque wrenches.
Does your Craftsman wrench have a little window you can see the torque value through?? If it does you have to remove the plastic piece at the end of the wrench. To do that you have to peel back the rubber boot and you will see two screws you have to remove. Be careful when you have removed them, they screw into two nuts that just lay in holes in the plastic end piece. When you remove the plastic end piece they can easily be lost. Now you should be able to unscrew the next piece inside the wrench. It is a cylinder with numbers on it with a long screw going through it. You have to loosen the nut on one end of that part and tighten the nut on the other end to move the cylinder to the point where the numbers agree with the torque. This gets easier after you have done a couple hundred of them. You can't really do a very good job comparing them to a beam type wrench. You really need a torque calibrator.
A couple of comments I have:
I don't understand how a dial wrench could be used to check a fastener that is already torqued, as suggested by the OP? Torque has to be measured while the fastener is turning. Please explain.
I have a digital Snap On Tech Wrench at work that vibrates and beeps at the desired torque. It displays the final torque, including if you overtorque. It is a natural tendency to add an "extra pull" at the end the same way many people push a little bit extra at the end of a brake stop. Snap On sets their wrenches a to go off a tad bit early to help compensate for this end-pull tendency. I would say that one just needs to learn better technique with these wrenches when completing the tightening. It takes practice and learned skills.
Finally, it is important for users to know that measuring torque via turning fasteners can be very imprecise due to faster condition, friction, and many other variables. It is common knowledge that torque can vary +/- 30% due to these variables regardless of the accuracy of the wrench. Just something to be aware of when arguing about one % difference claimed by wrench manufacturers.
I don't understand how a dial wrench could be used to check a fastener that is already torqued, as suggested by the OP? Torque has to be measured while the fastener is turning. Please explain.
I have a digital Snap On Tech Wrench at work that vibrates and beeps at the desired torque. It displays the final torque, including if you overtorque. It is a natural tendency to add an "extra pull" at the end the same way many people push a little bit extra at the end of a brake stop. Snap On sets their wrenches a to go off a tad bit early to help compensate for this end-pull tendency. I would say that one just needs to learn better technique with these wrenches when completing the tightening. It takes practice and learned skills.
Finally, it is important for users to know that measuring torque via turning fasteners can be very imprecise due to faster condition, friction, and many other variables. It is common knowledge that torque can vary +/- 30% due to these variables regardless of the accuracy of the wrench. Just something to be aware of when arguing about one % difference claimed by wrench manufacturers.
Good post by doitmyself.
OP, what are you seeing with the normal CDI/Snap-On clicker wrenches?
Thanks.
OP, what are you seeing with the normal CDI/Snap-On clicker wrenches?
Thanks.
I see the dial type torque wrenches come in that are used by Quality Assurance to check that fasteners have been properly torqued. I don't claim that has a lot of validity, but that is how many are used. You are correct about the digital wrenches, I just don't agree that you in actual practice get much more accuracy than a quality clicker type. For example, if you set the digital one to "buzz" at 150 inch/lbs you might easily see it display 156 inch/lbs when you complete tightening. That is a 2% error. When combined with a 2% inherent accuracy of the wrench you are back at 4% (most common tolerance for a clicker).
Originally Posted By: doitmyself
I don't understand how a dial wrench could be used to check a fastener that is already torqued, as suggested by the OP? Torque has to be measured while the fastener is turning. Please explain.
I couple my reference Beam wrench and my Clicker wrench together with a 1/2in 8-point socket that will fit a 1/2in square drive nicely. The two wrenches can then be compared. I have had to adjust my Clicker after a lot of use. They tend to undertighten after a lot of use and the adjusting screw on the Clicker has to be turned in to increase the torque.
I don't understand how a dial wrench could be used to check a fastener that is already torqued, as suggested by the OP? Torque has to be measured while the fastener is turning. Please explain.
I couple my reference Beam wrench and my Clicker wrench together with a 1/2in 8-point socket that will fit a 1/2in square drive nicely. The two wrenches can then be compared. I have had to adjust my Clicker after a lot of use. They tend to undertighten after a lot of use and the adjusting screw on the Clicker has to be turned in to increase the torque.
Originally Posted By: itguy08
Have you tested the Harbor Freight units? I have a few and hear they are pretty accurate.
I have tested a few of HF's 1/2 inch units. I work in the nuclear industry and we require calibrated equipment for QA purposes. My testing has been performed on NIST certified torque transducers. Straight out of the box the two wrenches I have tested were within +/- 2% of their readings at several set points.
Have you tested the Harbor Freight units? I have a few and hear they are pretty accurate.
I have tested a few of HF's 1/2 inch units. I work in the nuclear industry and we require calibrated equipment for QA purposes. My testing has been performed on NIST certified torque transducers. Straight out of the box the two wrenches I have tested were within +/- 2% of their readings at several set points.
Originally Posted By: redbone3
Part of my job is calibrating torque wrenches.
I LOVE BITOG for exactly this reason...such diversity.
Some many many years ago, when we were putting the power station in service for the first time, one of the graduate engineers was tasked with quality assurance on some High Voltage bus bars.
One of the technicians was using a torque wrench, and this graduate asked for the calibration certificate.
Technician, quick as a flash told him that he could provide it, but seeing as the torque wrench was calibrated in a laboratory at sea level, and we are 900m above sea level, it was only a guide at best.
Said graduate spent the afternoon ringing torque wrench suppliers asking for the altitude offsets/corrections...
Part of my job is calibrating torque wrenches.
I LOVE BITOG for exactly this reason...such diversity.
Some many many years ago, when we were putting the power station in service for the first time, one of the graduate engineers was tasked with quality assurance on some High Voltage bus bars.
One of the technicians was using a torque wrench, and this graduate asked for the calibration certificate.
Technician, quick as a flash told him that he could provide it, but seeing as the torque wrench was calibrated in a laboratory at sea level, and we are 900m above sea level, it was only a guide at best.
Said graduate spent the afternoon ringing torque wrench suppliers asking for the altitude offsets/corrections...
Originally Posted By: redbone3
To get the best accuracy on the clicker type wrench run them up to full scale and exercise them a few times. Then, return to the bottom of the scale and run them up to the torque setting you need. When finished always return the wrench to the lowest setting to preserve the spring.
I appreciate this post very much - and thank you!
I am trying to figure out how to utilize the above advice. My favorite wrench to use on lug nuts has max capacity of 250 ft-lbs. Maybe I could find the biggest lag bolt I've ever seen and drive it into the header above my overhead door and get a couple clicks at 250. Then I "only" have to worry about about cranking out 125# on the 25" wrench!!
To get the best accuracy on the clicker type wrench run them up to full scale and exercise them a few times. Then, return to the bottom of the scale and run them up to the torque setting you need. When finished always return the wrench to the lowest setting to preserve the spring.
I appreciate this post very much - and thank you!
I am trying to figure out how to utilize the above advice. My favorite wrench to use on lug nuts has max capacity of 250 ft-lbs. Maybe I could find the biggest lag bolt I've ever seen and drive it into the header above my overhead door and get a couple clicks at 250. Then I "only" have to worry about about cranking out 125# on the 25" wrench!!
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