How to test torque wrench?

[dandyZ]

I have a craftsman torque wrench. Not sure it's accurate. I used it once to torque my lug nuts to "spec" and 2 nuts fell off while driving! Not good. So how to test the wrench for accuracy?

[BLOZ UP]

I am having the same thoughts about mine. I imagined some contraption involving a known good wrench, a vice, some type of bearing or something to allow twisting through the vice, and two people pushing against each other and measuring the difference between the two.

Edited November 29, 2010 by BLOZ UP

[johnc]

I have a craftsman torque wrench. Not sure it's accurate. I used it once to torque my lug nuts to "spec" and 2 nuts fell off while driving! Not good. So how to test the wrench for accuracy?

 

Take it to a Sears store, they might have a way to test it. You can also nicely ask a Snap On truck driver to check it.

[mxgsfmdpx]

Take it to a Sears store, they might have a way to test it. You can also nicely ask a Snap On truck driver to check it.

 

And then they tell you "yep, it's off by 2 foot pounds, get rid of it" "Here is a 100 tooth 3/8th's drive torque wrench with an awesome comfy handle, and you're lucky, it's on sale today for only $400!!!"

 

[cygnusx1]

    Weights, broom handle, hose clamps, vise, and a calculator.  The broom handle and clamps are optional if the handle on your wrench is long enough to hang the weights, or you don't have a lot of weight.. You can use a pail of water.  Test a few different weights to check the full range of use.   Use locktite, cotter pins, or wire, on critical bolts.

 

 

 

 

Torque = Force x Distance

Edited November 30, 2010 by cygnusx1

[neotech84]

I am having the same thoughts about mine. I imagined some contraption involving a known good wrench, a vice, some type of bearing or something to allow twisting through the vice, and two people pushing against each other and measuring the difference between the two.

 

Testing or comparing two wrenches on a torqued fastener is NOT going to tell you if its good. Re torquing will add more force on the fastener thus increasing the torque. It's just like double clicking the wrench you will miss your range. I have seen a double click add over 100 inlbs or MORE!

 

You need to take it to a place that has a guage that will tell you the exact torque of your wrench.

 

Also a tip is to warm your torque wrench up by taking it to 50% of the value and click it 10 times to get the springs ready. Then return to within 10% of the LOWEST value (where it should be for storing).

 

My link

[19762802+2]

You could go to a Local discount tire, They always have a torque tester and I'm sure if they are cool guys they would be happy to test it for you or let you do it.

[BLOZ UP]

Testing or comparing two wrenches on a torqued fastener is NOT going to tell you if its good. Re torquing will add more force on the fastener thus increasing the torque. It's just like double clicking the wrench you will miss your range. I have seen a double click add over 100 inlbs or MORE!

 

I wasn't trying to say that. I was saying that you should hook two torque wrenches together, one known accurate one and the one in question, and torque them against each other. They should both read the same torque. I just couldn't sort out in my mind how to hold them both still without affecting the torque values.

[JMortensen]

I have a craftsman torque wrench. Not sure it's accurate. I used it once to torque my lug nuts to "spec" and 2 nuts fell off while driving! Not good. So how to test the wrench for accuracy?

When I write this it looks assholish, but it isn't intended that way. Do you have any idea what the proper torque should feel like? Just through experience I would think that most people would have a good enough idea of "tight enough" that they wouldn't trust a torque wrench that clicked for 70 ft/lbs when you were actually putting 35 ft/lbs through it. It makes me wonder if you dont have some other issue going on, like maybe you didn't snug the lug nuts down before you put the car on the ground so you got an inaccurate torque reading, or maybe the threads were bone dry or the lug nut was dragging on the wheel surface or something. Just seems impossible for lug nuts to literally fall off after torquing unless something else was going on.

 

I like Dave's test. It' can be done at home with some very simple math.

[BLOZ UP]

It's kind of hard to judge X lbs by feel, because X lbs feels the same at 8" or 16", which would be totally different torque values.

[Dan Juday]

    Weights, broom handle, hose clamps, vise, and a calculator.  The broom handle and clamps are optional if the handle on your wrench is long enough to hang the weights, or you don't have a lot of weight.. You can use a pail of water.  Test a few different weights to check the full range of use.   Use locktite, cotter pins, or wire, on critical bolts.

 

 

 

 

Torque = Force x Distance

 

Dang! Now I've got to go test mine. Wait, how do I know my scales are accurate when I weight my pale of water?!

[neotech84]

Dang! Now I've got to go test mine. Wait, how do I know my scales are accurate when I weight my pale of water?!

 

 

Just stand on it set it to zero and get back on with the bucket. Subtract the earths gravitational pull and divide by 9

[ModernS30]

You could go to a Local discount tire, They always have a torque tester and I'm sure if they are cool guys they would be happy to test it for you or let you do it.

????

 

Once again, I work at Discount Tire, I have NEVER heard of having one. Worked at one in NM and 2 different locations in Indiana, had 3 different manager, non of them have said anything about such a thing.

[19762802+2]

????

 

Once again, I work at Discount Tire, I have NEVER heard of having one. Worked at one in NM and 2 different locations in Indiana, had 3 different manager, non of them have said anything about such a thing.

 

Well we have one here in Colorado springs, I have personally seen it. Maybe they got one because we are always breaking or dropping ours.

[cockerstar]

A quick google brought up this link that I found to be pretty interesting

http://www.algeo.com/~joe/KIAT/kiat_3.htm

[cygnusx1]

I wasn't joking about weights and a vise.

[Tony D]

There are actually little torque attachments available for around $80 that will turn any breaker bar into a torque wrench. They read out the torque as you approach your setpoint and then give an audible tone and light a series of LEDs to indicate final numbers.

 

Using one of them with one end clamped in a vice will tell you, and they are strain gauge-based so not as prone to stray as springs and click mechanisims. (Basically the same internals, though not as precise or calibrated as the device Neotech84 posted.)

 

I have one for each smaller size drive: 1/4, 3/8, 1/2"

 

When I travel overseas, I tend to take these three instead of torque wrenches, because though Distributors are SUPPOSED to have the proper tools for precision work, in Asia sometimes this isn't the case. It lets me get comfortable with the torque wrench they have, or make one out of their breaker bar.

 

As for 'feeling the correct torque' I had a manager who thought the same way "A good mechanic doesn't need a torque wrench." My retort was that I hoped he felt the same way when the plane falls out of the sky... Click Wrenches have drawbacks...

[neotech84]

As for 'feeling the correct torque' I had a manager who thought the same way "A good mechanic doesn't need a torque wrench." My retort was that I hoped he felt the same way when the plane falls out of the sky... Click Wrenches have drawbacks...

 

 

I agree 100% with you Tony. I am currently employed in the aviation industry and work with torque calibrated tools on a daily basis. The digital wrenches are worth every penny as most will tell you what the final torque was. Just don't drop it!

[JMortensen]

I really wanted to do this test but my bench that my vise is mounted to is flimsy enough that I tried to test a swaybars's spring rate and was WAY off. The itch to try again hit me and so I took one of my cherry pickers and welded a socket to the mast and tested both my Craftsman 1/2" clicker and my 3/8" Harbor Freight clicker. I was under the assumption that the HF wrench was a POS and was actually putting out a lot more torque than it showed. Turns out I was wrong. I tested the HF at 10, 15, and 20 lbs and it was within a lb on every setting. It goes up to 75 lbs or something, but I wouldn't use it for anything higher than about 25, so I didn't test it all the way up the scale. I tested the Craftsman (which has had about 15 years of abuse and has frequently been put away without being zeroed) and found that at set at 30 lbs it was actually giving about 28 lbs of torque and at set at 75 it was actually giving around 78 lbs. Pretty good on both counts!!! Thanks again Dave for the suggestion. This is something that I've thought about for a very long time and never managed to test.