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Torque Wrenches

Re my previous post, found a nice youtube vid on how to do this with a simple luggage scale.
[YOUTUBE]XaqBA-xSGbc[/YOUTUBE]
 
How accurate do you think a $5 luggage scale is?
 
dravnx said:
How accurate do you think a $5 luggage scale is?
Click to expand...

Sure - any measurement is only going to be as accurate as the gauge or scale by which we use as the basis for the measurement. That said, even cheap strain gauges like you'll find in that digital luggage scale can perform respectably well. (Welcome to world of modern electronics and other semiconductor devices.)

While tool companies are using NIST traceable scales to calibrate a torque wrench, for the casual Joe in the garage, this isn't a bad way at all to double check an old wrench. It's not rocket science - the 'pro' method isn't fundamentally different, and the dude covers most of what you'd need to know in a simplified way in that video. As you can see, even any angular error introduced is minor if you make a remote error to pull perpendicularly to the torque wrench. T = r x F.

FWIW, I'm a physicist by day. Would I use this method in my home garage if I had a nice scale? Sure. Would I use it on a funded defense project? Nope. But honestly... When was the last time the average person checked the reading on the wrench against any standard, let alone had it calibrated back at the factory or any other servicing individual? (For most people, I bet never!) They just blindly accept the reading and move on.
 
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Kestrel said:
When was the last time the average person checked the reading on the wrench against any standard, let alone had it calibrated back at the factory or any other servicing individual? (For most people, I bet never!) They just blindly accept the reading and move on.
Click to expand...

So I guess we're not average. :party
 
I'm OK with not being average.
Seriously, it costs $45 to get a torque wrench cal'd.
 
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ThinkFast said:
Easy enough to find out. Get yourself a ten lb bag of flour and find out.
Click to expand...

what's the std deviation on the weight of a bag of flour?

although I guess big food is probably pinching pennies to extract maximum revenue

....but then again, they can't risk underfilling a bag, less the risk egg on their face in a scandal for screwing the consumer
 
Kestrel said:
Sure - any measurement is only going to be as accurate as the gauge or scale by which we use as the basis for the measurement. That said, even cheap strain gauges like you'll find in that digital luggage scale can perform respectably well. (Welcome to world of modern electronics and other semiconductor devices.)

While tool companies are using NIST traceable scales to calibrate a torque wrench, for the casual Joe in the garage, this isn't a bad way at all to double check an old wrench. It's not rocket science - the 'pro' method isn't fundamentally different, and the dude covers most of what you'd need to know in a simplified way in that video. As you can see, even any angular error introduced is minor if you make a remote error to pull perpendicularly to the torque wrench. T = r x F.

FWIW, I'm a physicist by day. Would I use this method in my home garage if I had a nice scale? Sure. Would I use it on a funded defense project? Nope. But honestly... When was the last time the average person checked the reading on the wrench against any standard, let alone had it calibrated back at the factory or any other servicing individual? (For most people, I bet never!) They just blindly accept the reading and move on.
Click to expand...

I look at calibration cost as cheaper than a hospital visit copay if something wasn't torqued properly through tool error
 
GPToyz said:
I look at calibration cost as cheaper than a hospital visit copay if something wasn't torqued properly through tool error
Click to expand...

Sure thing. I'm just emphasizing that it's not impossible (or even remotely hard) to calibrate a wrench yourself as long as you've got a decent scale.

I don't think most people worry about applying an excess of torque; rather, they're trying to avoid exceeding the limits of a given fastener, and shearing something off. An average moron at a 10 minute oil change place certainly doesn't have a problem cracking the shit out of somebody's oil pan :x

Like I said, I'd bet most casual folk have never had a wrench calibrated or checked. Given the ease with which you *can* check it (and adjust it), I welcome any simple video like the one above that would encourage people to look into the calibration of a wrench for themselves. Education is the first step! :thumbup
 
GPToyz said:
I look at calibration cost as cheaper than a hospital visit copay if something wasn't torqued properly through tool error
Click to expand...

I'd be more worried about someone blindly entering an incorrect value on their torque wrench then blindly accepting the result.

The only time I've had a fastener back-out, and nearly kill me, was the last time I had a professional mechanic from a well-respected shop in SF change a rear tire for me. I watched the guy put a torque wrench on the axle nut just before handing the bike back to me... and it promptly fell off 60 miles later. By the time I noticed it the rear axle was, quite literally, inserted in the swing arm by a single thread. Tightening that nut without a torque wrench probably would have produced significantly better results for me...
 
fubar929 said:
I'd be more worried about someone blindly entering an incorrect value on their torque wrench then blindly accepting the result.

The only time I've had a fastener back-out, and nearly kill me, was the last time I had a professional mechanic from a well-respected shop in SF change a rear tire for me. I watched the guy put a torque wrench on the axle nut just before handing the bike back to me... and it promptly fell off 60 miles later. By the time I noticed it the rear axle was, quite literally, inserted in the swing arm by a single thread. Tightening that nut without a torque wrench probably would have produced significantly better results for me...
Click to expand...
Same kind of thing happened to me. The one time I've used a torque wrench to tighten an oil drain plug it vibrated loose and started leaking.
 
You can't blame the wrench, blame the nut on the handle of the wrench.
 
Another problem (probably not in the case of the axle nut though) is the diff between dry and wet torque. Most torque ratings are for dry, but put anti-seize etc on it and you may overtorque it. Opinions vary so do your own research but I've seen a **40%** torque reduction claimed on wet vs dry bolt. Useful: https://www.fastenal.com/en/83/torque-calculator
 
dravnx said:
I'm OK with not being average.
Seriously, it costs $45 to get a torque wrench cal'd.
Click to expand...

I think that is more than I paid for both of the Pittsburgh wrenches I bought recently. :laughing (and I never realized that there is a city named Pittsburgh in China)

wakked1 said:
Another problem (probably not in the case of the axle nut though) is the diff between dry and wet torque. Most torque ratings are for dry, but put anti-seize etc on it and you may overtorque it. Opinions vary so do your own research but I've seen a **40%** torque reduction claimed on wet vs dry bolt. Useful: https://www.fastenal.com/en/83/torque-calculator
Click to expand...

It just keeps getting worse. I'm going to have to get my wrenching religion on and just "believe" my torque wrenches are good for go.
 
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I'll just throw this into the mix for what it's worth...

Building on what dravnx said- the reason for torquing is to achieve a certain clamping force via bolt stretch, and there are much more accurate methods for achieving a specified clamping force than using torque. These range from crush washers to springs between the bolt head and the material to hand tightening the nut and putting a dial indicator on the bolt while turning the nut and measuring the actual stretch.

Bolt torque is just about the most round about way you can go for measuring clamping force, as there are so many variables at play. In the best of circumstances where the manufacturer specifies new, lubricated bolts of a certain variety being installed in a clean environment into new threads (bolts inside the engine come close to this), torque value will get you within roughly 25% of the design clamping force at best. This is if your torque wrench is dead nuts on.

In order of least to most accurate methods
Torque wrench<angle indicator<crush washer<spring under bolt/dial indicator method<strain gauge/ultrasonic

Where the most accurate methods deviate less than 5% from the design clamping force.

So, in my opinion, as long as your torque wrench is not terribly inaccurate, it's just fine. Cause you're not getting reliable clamping force anyway :p
 
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I have two torque wrenches, a Sears Craftsman torque wrench that I use exclusively for high torque applications. Since the "click" is not as discernible on light torque applications, I use a beam type torque wrench for those. Works for me... :)
 
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