Torque Wrench Max Force (150 or 250)

[dougcoug]

I am in the market for a 1/2" torque wrench and I am finding most of the max torque settings on them are around 150 ft lbs or 250 ft lbs. I will be using it for mostly automotive work so I am wondering what cases will be needed for 150+ of force. My truck needs 140 ft lbs for the wheels but I haven't found anything greater than that. If I buy the 150 max torque wrench now, I don't want to have to buy at 250 later. Does anyone know of instances that you will need more than 150 ft lbs of force or did anyone buy a 150 ft lbs torque wrench and regret it later? Thank you.

 

[krusty the clown]

you may never need to torque anything tighter than 150 ftlb but they are the same price why not?

 

[Charles (in GA)]

Lets compare two tools, both Sturtevant Richmont micrometer type ratchet head.

The 4SDR150 has a range of 30 to 150 ft/lbs, in 1 lb increments, and is 18" long.
The 4SDR250 has a range of 50 to 250 ft/lbs, in 2 lb increments, and is 24" long.

Typical of most torque wrenches, they are assured an "Accuracy of +/- 4% Indicated Value from 20% to 100% of capacity" This means the bottom 20% of the range is not to be considered accurate. On a 30 to 150 range, this means that anything below 54 ft/lbs is not considered accurate, while on the 50 to 250 range anything below 90 ft/lbs is not considered accurate.

Do you want to wag around a 2 ft long tool that is not accurate below 90 ft/lbs?

One tool does not fit all!

Charles

 

[Treeman]

Respectfully, I think your explanation is wrong, Charles.

PI states: "Accurate within 3% of reading from 20% of full scale to full scale"

CDI states: Accuracy: ± 4% clockwise ± 6% CCW of indicated value, CW, from 20% to 100% of full scale


Full scale is 150 or 250 lb. ft. . 20% is 30 and 50 lb. ft.

So, in your examples, the wrenches are accurate from 30 to 150 lb. ft. and 50 to 250 lb. ft.. In other words, the wrenches are not accurate below 20% of FULL SCALE.

With the big wrench, you lose 20 lbs. at the low end. With the small wrench you lose 100 lbs. at the high end.

Best, is to get one wrench around 20 to 100, and another at 50 to 250 to cover everything. Of course, an inch lb. wrench may also be needed to cover below 20 lb. ft. !!!!!!

 

[Charles (in GA)]

I figured someone would jump on that. If you figure that "20% to 100% of capacity" means that on a 50 to 250 ft/lb torque wrench that the accuracy is based on zero to max then the entire range of the tool is useful, (20% of 250 is 50 lbs, and the bottom 20% of 250 would be that area that is off the scale anyhow), and in the example of the 150 lb max, 20% of zero to 150 is 30, which again is off the bottom of the scale, so why would they bother making the statement anyhow? if that were the case they simply could say the tool was accurate the full range of the scale.

Actually the CDI and PI examples make it even clearer by using the words "Full Scale" which to me, means just that, full scale, nothing above, nothing below.

What I'm saying is that the bottom 20% of the scale is not accurate. The scale is 30 to 150 or 50 to 250. Twenty percent of a 30 to 150 scale is 24 lbs, thus the bottom 24 lbs of the scale is not useful. With the 50 to 250 scale, 20% of the scale is 40 lbs, thus the bottom 40 lbs of the scale is not accurate.

The truth is, these torque wrenches are accurate at all settings, but due to manufacturing tolerances, they cannot be assured it will always be so.

Time to email some torque wrench companies to clarify this.

Charles

 

[Treeman]

The big three manufacturers don't have direct website answers to our debate. CDI is the closest, with this page: http://www.cditorque.com/main.html

"It is for the above stated reason that systems which have accuracy as related to indicated value should state the useful range to be 10% to 100% of the tester range.

Therefore, if a tester has 100 ft. lb. maximum range, it should not be used at less than 10 ft. lbs. if the desired accuracy is needed."

The 10% in this case is an example, not to be confused with the 20% we are debating.


Edit....that link takes you to their main page. You have to go to torque facts, then indicated vs. full value.


I can't find any authoritative sources, but I will lob a few more internet sources that concur with me (cry uncle, when ready!):

http://www.buyerzone.com/construction/rbic-torque-wrench.html
right hand orange box: "When manufacturers state the accuracy of their torque wrenches, you may read qualifying statements, such as "Accuracy of plus/minus 3 percent Indicated Value (from 20 to 100 percent of capacity) exceeds ASME B107.14M and ISO 6789."

In this instance, the manufacturer is cautioning you against using the bottom 20 percent of the wrench's capacity. Assuming that the scale of a 150 pound-feet wrench starts at zero, you'd want to avoid taking readings below 30 pound-feet, because these readings may not meet stated accuracies. "

http://www.webbikeworld.com/r3/torque-wrench/

"For example, our model C2FR100F has a capacity of 20 to 100 ft. lbs. It is rated at ±4% accuracy, from 20% of its highest rating to the end of the scale. That means that the ±4% accuracy rate on this wrench is valid from 20 to 100 ft. lbs., in this case, across the entire range of the wrench."

http://www.psicylinders.com/library/Current/torque_wrench.htm


I have seen many wrenches that have scales below the "20%" of "full capacity". Craftsman says it's 3/8" microtork wrench scale is from 10 to 75 lb. ft. (but not accurate below 15 lb. ft. by my definition).

Beam and dial scales go down to 0. Yet, by my definition, they are not accurate below 20% of their FULL scale or capacity.

I do understand your logic. But, I'll bet my wife that I'm right (she's an awesome cook, as well as excellent at other things).

 

[Charles (in GA)]

OK, made a phone call, I'm all wet, totally wrong.

Needed to talk to someone in person, PI and SR are closed for the day, CDI hasn't returned the call, Norbar USA is closed, UK is late at nite. Needed someone who spoke English, called Norbar in Adelaide, Australia. Talked to a nice guy there who said "full scale" didn't mean the scale on the tool, but from zero to the max of the scale (no logic in that), therefore, virtually every torque wrench is accurate within the specified precentage for the full range of the tool, such as 30 to 150 is 20% to 100% or 50 to 250 is 20% to 100%.............................

So, why in the Hell don't they say that! rather than beating around the bush? The bottom 20% of the tool is outside the capabilities of the tool anyhow!

He did tell me that British Standard 6789 is the defining document for this, have to read up some more.

Sorry for any mis understanding.

Charles

 

[Treeman]

Charles, I added a few edits while you were calling Australia, just to add salt to the wounds.

PLEASE, EVERYONE NOTE CHARLES' PERSISTENCE WENT WELL ABOVE MINE.....HE CALLED AUSTRALIA TO GET THE ANSWER!!!!!!!

For the effort, I will still ship my wife off to you.....UPS???? Note that she can cook grits, even though she is from Michigan.

 

[Bo Heck]

Note that she can cook grits, even though she is from Michigan.

lol