Flex-Head Torque Wrench

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22,707
Location
CA
I am in the market for a 3/8" drive clicker torque wrench and I plan to make my purchase this week. I think I've decided on the CDI metal-handle torque wrench, but I am undecided between the rigid-head and the flex-head. The flex-head one flexes 15 degrees. It doesn't seem to be very much, so I was wondering if it'll be of any use to me. So far, I've never had any use for a flex-head torque wrench. I personally prefer the rigid-head version as it covers 5-75 ft-lbs while the flex-head covers 10-80 ft-lbs, but if the flex-head will be useful I'll just purchase it. What do you guys think? http://cgi.ebay.com/CDI-TORQUE-WRENCH-75...93%3A1|294%3A30 http://cgi.ebay.com/CDI-TORQUE-WRENCH-FL...93%3A1|294%3A50
 

JHZR2

Staff member
Messages
44,841
Location
New Jersey
Flex ratchets can be dangerous, IMO. A torque wrench is used differently, and is not. IMO, for doing stuff on the ground, in a DIY scenario, where there may not be the best clearance, having that bit of freedom can help. Im thinking of doing differential drain plugs as an example where Ive liked the flex. At the same time, I suppose a wobble extension can do about the same thing. I do not believe that the flex will effect the torque, as the flex vector is in a different axis than those relevant to the torque. It will simply and effectively cause a slight decrease in the lever arm. This will make it harder in terms of arm strength (likely not noticable), but the mechanism inside should not be able to tell the difference.
 
Messages
7,742
Location
MI
At work, I have the Precision Instruments split beam wrenches in the 3/8" and 1/2" drive sizes and a 1/4" drive Snap-On Tech wrench for inch lbs.. All are flex head and I like them very much. The flex head is very solid, moves very stiff, and does not flop around. Numerous times I have had situations where just a few degrees of flex allowed me to torque without using an extension. To me, it seems that the use of an extension increases the odds of applying indirect "sideways" force that would increase torque errors vs. having a short socket directly on the end of the wrench. Just my perception, especially with any extension over 3 inches. Regarding your concerns about torque ranges, remember that almost all torque wrenches are calibrated accurate down to 20% of their full scale. Your 75 ft. lb. is good down to 15 ft, lbs., and the 80 is good down to 16 ft. lbs.. Neither of these wrenches would be safe for most spark plugs that are generally in the 13 ft. lbs +/- range. Critic, you know where to go for the most opinions...hint, GJ!
 
Messages
2,260
Location
NY, NY
I have a few torque wrenches. All but two are flex head. The dial type in lb wrench and my 3/4 drive wrench are bith fixed head. All my others are flex. I'll say they were definitely helpful. I always try to pull as straight as possible, but sometimes a couple of degrees of flex is a lifesaver.
 
Messages
2,431
Location
Toronto, Canada
 Originally Posted By: JHZR2
Flex ratchets can be dangerous, IMO. A torque wrench is used differently, and is not. IMO, for doing stuff on the ground, in a DIY scenario, where there may not be the best clearance, having that bit of freedom can help. Im thinking of doing differential drain plugs as an example where Ive liked the flex. At the same time, I suppose a wobble extension can do about the same thing. I do not believe that the flex will effect the torque, as the flex vector is in a different axis than those relevant to the torque. It will simply and effectively cause a slight decrease in the lever arm. This will make it harder in terms of arm strength (likely not noticable), but the mechanism inside should not be able to tell the difference.
The flex will affect the torque, but, at fifteen degrees, probab ly no more than 5%. Take the extreme case, when the flex angle is 90 degrees. All the force applied to the handle will be used to 'bend' the stud you are tightening a nut onto, none of the force will be applied as torque to turn the nut.
 

The Critic

Thread starter
Messages
22,707
Location
CA
 Originally Posted By: doitmyself
Regarding your concerns about torque ranges, remember that almost all torque wrenches are calibrated accurate down to 20% of their full scale. Your 75 ft. lb. is good down to 15 ft, lbs., and the 80 is good down to 16 ft. lbs.. Neither of these wrenches would be safe for most spark plugs that are generally in the 13 ft. lbs +/- range. Critic, you know where to go for the most opinions...hint, GJ!
I called Precision Instruments this morning and the technical representative told me that their split-beam torque wrenches are good for 20% of their full scale. As an example, he explained that their 3/8" flex-head model is good for 20% of the 0-100 scale, which is why it was rated for 20-100 ft-lbs. Within that range, accuracy is within 4%. I originally thought otherwise, but two different Precision Instrument reps confirmed the above information.
 

The Critic

Thread starter
Messages
22,707
Location
CA
Just received the PI Split Beam torque wrench today. It appears to be a well-built product. I'll be using it tomorrow morning when I replace my spark plugs. Let's hope that it was worth the $106 that I paid for it.
 
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