[Lear35A]

Last week I had the chance to play with a torque wrench checker. This is a device that measures the actual torque the wrench is developing when it "clicks." These are used for calibrating this type of wrench.



What surprised me is the big difference you get based on technique. If you rush by pulling hard or quickly or with a jerk, the torque at the click point is about 10% too high. A smooth, slow approach to the click point gives you what you actually set. This seemed to be true for a wide range of torques. And when I say slow, I mean very slow. I never felt I had been using these things incorrectly in the past, but I had. Sloooow + Smoooth = proper torque.



I was doing this with my Craftsman 3/8" drive wrench with a range of 10 to 75 ftlbs. I'll be back there next week and give it a try with my smaller and larger wrenches to see if there's any difference.

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[mbardeen]

Yes, they also say that try to get the correct torque during the middle of a pull (probably for the same reason you mentioned). Also, use the correct range torque wrench. Values in the middle of the range will be more accurate than those at the extremes.



Or so says Stephan Wilkinson (author of the Gold Plated Porsche).

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[flash]

yup to all of the above.



when the rating is critical, due either to fragility or compression issues, (i.e. spark plugs and such) i always use a needle type, and not a click type, so that i can see the torque building.

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[Grandpa#3]

Torque Wrenches also need to be calibrated every so often. If they are used frequently with proper care calibration should be every 6 month or sooner. If dropped or knocked around it will need to be calibrated again as it will not be accurate. The bar and needle is what I have always used at home for larger bolts/nuts and 3 foot long clicker 1 inch drive calibrated torque wrenches in the military. The PMEL, Precision Measurement Lab, always kept the wrenches properly calibrated.



Cheers,

Larry

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[flash]

another thing to remember about "click type" torque wrenches is to reset it to zero when you are done. if you store it with the handle turned to a setting, you will screw it up in short order.

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[MB968]

[quote name='Lear35A' timestamp='1357142183' post='136935']

Last week I had the chance to play with a torque wrench checker. This is a device that measures the actual torque the wrench is developing when it "clicks." These are used for calibrating this type of wrench.



What surprised me is the big difference you get based on technique. If you rush by pulling hard or quickly or with a jerk, the torque at the click point is about 10% too high. A smooth, slow approach to the click point gives you what you actually set. This seemed to be true for a wide range of torques. And when I say slow, I mean very slow. I never felt I had been using these things incorrectly in the past, but I had. Sloooow + Smoooth = proper torque.



Lear, did you calc. accuracy and repeatabilty values for the Craftsman. I'm curious how the numbers turned out.



I was doing this with my Craftsman 3/8" drive wrench with a range of 10 to 75 ftlbs. I'll be back there next week and give it a try with my smaller and larger wrenches to see if there's any difference.

[/quote]



Yeah, one of the labs that reported to me in R&D was our Gauge and Calibration Lab. They took care of over 24,000 gauges and instruments that were recalled on a regular basis for recertification. I can confer with: slow and easy gives the most accurate reading; staying away from the botton and top 10% of the range is also good practice; use of a bar type for checking your click type every so often is good for the DIY'er (reminds me I should be following this same advice).

Lear, did you calculate the accuracy and repeatibility values for the Craftsman. I'd be curious how they came out.

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[Cloud9...68]

Interesting, and this highlights a possible advantage to the needle type torque wrench. With this type of wrench, I can very readily see the impact of the smoothness of the pull on the apparent accuracy of the reading. A slow, steady pull causes the torque reading to build gradually but steadily, while sudden, jerky movements give what look to be more spurious readings. This forces you to use good technique. With a click type wrench, you can't see the torque values, so there's no way of knowing if you're using the most optimal technique.

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[gbarrier]

Ditto on the old bar type wrenches when you can and periodic calibration on both type.

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[Lear35A]

I did not do a statistically significant number of tests to report true accuracy or repeatibility. However my Craftsman when pulled smoothly and slowly was within one or two ftlbs. I did not see worse figures at the high and low end of the range. This is for this one wrench and a limited number of test points. I've had the wrench for a long time, don't treat it in any special way and its never been calibrated since new. I do dial it down to zero after I use it.



Frankly I'm happy with the click type wrench. Even more so now that I know how to use it better. As good as an untested, uncalibrated pointer type. IMHO, of course.



I'm bringing all 3 of my clickers next time and will do more testing.

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[MB968]

Let us know how the rest turn out when you test them. I'm curious. I know we had a lot of each of the typical brand named torque wrenches in our factory. I don't recall there being much of an issue with them over time unless they were abused in service.



And, as I've said before in posts, A small margin of error in tightening screws should not be an issue. Designs are never put that close to the limit that small errors high or low should be an issue. Of course, if the female theads have been abused (overtorqued by someone not using a torque wrench), or are overly worn from use, or you get pickup damage, etc. you can have failures. But that's what helicoils were made for.

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[rhudeboye]

Good tip. I didn't know the pace you turned the wrench was an issue. Perhaps the brand makes a difference in how fast you can pull as well. Say a $30 harbor freight wrench requires a very very slow turn while a $200 Craftsman handles a faster speed well.

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[flash]

i've tested the 1/2" drive click type harbor freight and crew line wrenches - absolute junk. worthless for anything but lug nuts at the track. i've had 2 now and they both lost accuracy by the time they were a year old. after that, i just used them as a big breaker bar/lug wrench

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[MB968]

Yeah, I wouldn't buy anything that requires precision from HF. I find there stuff to be very low quality junk. If it is a simple item like an engine stand, where it is just metal pieces bolted together they seem to be OK. But any kind of tool, I buy elsewhere.

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[rhudeboye]

Agreed. BTW, the HF wrench goes for 19.00 not 30 LOL



I do own a set of work lights and the often advertised multi tool from HF. No issues thus far. I'm glad HF is around for Items like those.

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[Cloud9...68]

I have to say, Harbor Freight's quality has improved quite a bit in recent years. I recently bought a set of curved wrenches to access the top two bolts that attach the torque tube to the bell housing, expecting them to be junk, but actually, they're quite nice, and did a great job. Don't know how I got those danged bolts off without them - with a lot of coloorful language, as I recall. Their dial deflection indicators seemed to do a decent job on the cam timing as well.

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