Torque Wrench Questions

[The Critic]

Hey y'all,

I have two torque wrench questions:

1) I have an opportunity to purchase a near-new Snap-On QD3R250 torque wrench for $125 shipped. The owner of the torque wrench has used it less than a dozen times.

From what I understand, the QD3R250 has a 50-250 ft-lb range with a 20% to full scale accuracy. So, does that mean the wrench is only accurate from 90-250 ft-lbs?

If so, does this mean if I tried to torque some 80 ft-lb bolts with this wrench, the accuracy would be "a shot in the dark?"

2) I have been considering the purchase of either a Snap-On Techwrench or a Snap-On QD2FR75. Does anyone have any experience with the durability of the Techwrench? How does it compare to the click-type Snap-On model, especially in terms of accuracy? Snap-On did tell me though, that they can perform a complete rebuild and recalibration of the Techwrench for $80, which is extremely reasonable in case I ever need it.

Thanks!

 

[tj90]

Somethings missing in your statement "20% to full scale accuracy". Usually torque wrenches specify an accuracy of say +/-3% from 20% to full scale and +/-5% under 20% full scale...

 

[benjamming]

tj,

SO, CDI, PI, etc. just specify accuracy from 20% to 100% of full scale.

 

[franzdom]

The electronic ones are more accurate and they don't have to be relieved of tension when stored. The main problem is making sure you don't have a battery leakage in it. If you are casual you may want to remove the batteries between use. If you have a mechanical one those are probably better for most casual users.

 

[JayR]

based on my limited experience, tj90 is correct. The way to apply the accuracy number within the range is just multiply. +/- 3% at 80 lb ft means +/- 2.4 lb ft. That is, expect the actual torque to be between 82.4 and 77.6 lb ft. That is 80 plus 2.4 to 80 minus 2.4.
The 2.4 comes from 80 times 3% (which is .03 decimal).
My torue wrench question for y'all is that a friend tells me to NEVER use a torque wrench to break free a bolt/nut. Is this true and why?

 

[country83]

Hey y'all,

I have two torque wrench questions:

1) I have an opportunity to purchase a near-new Snap-On QD3R250 torque wrench for $125 shipped. The owner of the torque wrench has used it less than a dozen times.

From what I understand, the QD3R250 has a 50-250 ft-lb range with a 20% to full scale accuracy. So, does that mean the wrench is only accurate from 90-250 ft-lbs?

If so, does this mean if I tried to torque some 80 ft-lb bolts with this wrench, the accuracy would be "a shot in the dark?"

No. Full scale is 250 ft-lbs, so 20% of that is 50 ft-lbs. Anywhere on the wrench that is marked, it will be accurate.

 

[Charles (in GA)]

No. Full scale is 250 ft-lbs, so 20% of that is 50 ft-lbs. Anywhere on the wrench that is marked, it will be accurate.

This is correct. "full scale" means zero to top of the scale. Thus, a torque wrench that has a top of scale of 100 ft lbs would be accurate from 20% of that, or 20 ft lbs right to the top, 100 ft lbs. This 20% is a industry standard and specified by national standards in the US, EU, Britain, and Australia, to name a few.

I had the same misunderstanding a year or so ago, in the middle of the night, went so far as to call Norbar in Oz just to clarify the issue.

Charles

 

[Charles (in GA)]

My torue wrench question for y'all is that a friend tells me to NEVER use a torque wrench to break free a bolt/nut. Is this true and why?

He is correct, it is not good for the mechanism. Some torque wrenches will only click torquing clockwise, others will click and are accurate going either way, but the mechanism does not like to have its limits exceeded. Some, like the Precision Instruments split beams had a CW only ratchet, as going CCW would destroy them.

Charles