Torque Wrench Spec Question

[mikester]

I have another thread asking about torque wrenches but this is a little different.
What does it mean when it says Torque accuracy of +/- 3% CW between 20% and 100% of wrench capability. I understand what the +/- means but what is the 20% and 100% ? Ive seen all different figures for that.

 

[515Dave]

If the wrench goes from 50-250 ft-lbs, 20% would be 50 ft-lbs (20% of 250) and 100% would be 250 ft-lbs (100% of 250).

 

[mikester]

If the wrench goes from 50-250 ft-lbs, 20% would be 50 ft-lbs (20% of 250) and 100% would be 250 ft-lbs (100% of 250).

What if its a 20-150lb ? Im not understanding this. LOL

 

[visionguru]

**% means **% of the maxium torque.

For a torque wrench with maximum 150ft-lb, 20% means 30ft-lb.

The following is my old post about the accuracy of a Harbor Freight $10 torque wrench, you can see the accuracy difference at different torque settings:

I had Harbor Freight 3/8" 5~80 ft-lb torque wrench for over 10 years. It's not working anymore due to rust. I brought it to Harbor Freight, they simply gave me a new one as "life time warranty" replacement.

The following are the results, comparing against a Powerbuilt digital torque adapter:

Torque setting (ft-lb) Reading #1 Reading #2 Reading #3
10 ==============> 9.8 10.5 10.7
20 ==============> 19.3 20.6 19.7
30 ==============> 29.2 29.3 29.6
40 ==============> 40.5 40.1 40.4
50 ==============> 51.0 51.0 50.8
60 ==============> 62.8 63.0 63.0
70 ==============> 72.5 72.7 73.7

It is most accurate at 40 ft-lb (about 1% error), 30 and 50 (about 2% error), at lower and higher end of the range, the error is about 4%~5%. Not bad for a low cost torque wrench, but we can clearly see the non-linearity of the accuracy.

My Snap-On Techangles seem all within 1% across the range, even though I didn't do a thorough test.

IMHO, if you are doing anything requires accuracy (such as engine work), digital is the way to go. The old clicker type, no matter the brand, is inherently not as accurate.

 

[mikester]

So, if its a 3%+/- between 20-100% anything under the 20% would be less accurate ?

 

[country83]

So, if its a 3%+/- between 20-100% anything under the 20% would be less accurate ?

Correct. Depending on the wrench it may not even click.

Sent from my XT1635-01 using Tapatalk

 

[Treeman]

Yes, that is correct. The torque wrench calibration process only "guarantees" the +/- 3% accuracy from 20% of the (full) scale to 100% of the (full) scale. That is the useful range of that wrench. A 100 ft. lb. wrench is only calibrated accurate from 20 ft. lb. to 100 ft. lb. even if the scale goes down to 10 ft. lb. Just the way it is!