Torque Wrenches


#1

I have a couple of torque wrenches that I use whenever I should, and I’m wondering about how much I should worry about accuracy / calibration. Both are the “click-type” (or whatever you call it). Do these generally remain reasonably accurate? If I wanted them checked / calibrated what kind of business would do such a thing? (And if the answer is a local mechanic, how do I know theirs are correct?)



The details:



One is a Craftsman (20-150 ft.lb) and its pretty old (10+ years). I am a weekend shadetree guy so it doesn’t see a lot of use. When not in use it stays in its original packaging and its never been abused (I only use it at torque time and haven’t dropped it or run it over or anything).



My other one is only about 1yr old - it is an AmPro from Advance AP (120-960 in.lb) - same usage notes.



Any help / advice appreciated.


#2

When not in use you should back off the screw that sets the torque so that the spring is not held in compression while being stored. That is at least the instructions on my click style torque wrench.

I have checked my own by putting the 1/2 drive square in a secure vice and hunging a 10 and 20 lb weight normal to the wrench handle at a 1 foot moment arm. Do the math and hang it at what ever length is practicle for you. It has always confirmed accurate for me on my Harbor Frieght 20 year old wrench. I’m comfortable with that. I know I am only confirming the low end of the range but the spring should be linear.

If you have serious concerns and don’t mind spending some money look in your local phone book for calibration services. These services will charge an arm and a leg if you want a certificate tracable to the NBS.

I don’t know what Sears would say if you called them and asked for advice on calibrating your craftsman. Is it guaranteed for life?


#3

As long as you zero them out when you’re finished with them, and they’ve never been dropped, they should last forever. Also, never use a torque wrench as a breaker bar. (I’ve seen somebody do that).

Tester


#4

Broken torque wrenches make good breaker bars, but sadly, if you use it like that once, it’s a breaker bar forever.


#5

And never use it to break loose a bolt!!!


#6

PMEL checks them. You may be able to find one locally. Precision measurement equipment lab is what it stands for. It may have a lot of other names too. Maybe the place where you bought it will know of one or at least dumb looks are free of charge.


#7

Many thanks folks!

Of course, I read the first post by nbpt100 and did one of those smack myself on the forehead things wondering why I often miss the very simple but very wise approach. I’m just going to go hang some weights on them once in a while. (I actually think I might try using my digital fish scale).

I never have used it as a breaker bar (but thanks for checking!). But I also don’t literally -zero- it out each time. I back it down to somewhere in the lowest range - thats the only way they fit back in the case. But I’ll check them and then start taking them down to zero.

Thanks again to all.


#8

They wear out and loose accuracy over time. At work, where the torque wrenches are used all day, they only last a couple of months. We have a torque calibrator and check them monthly. I took my personal torque wrenches in and my older 1/2" drive is about 10# low at the 86 ft/lb setting. My newer 3/8" drive just broke so I got a new one. I keep mine at zero when not in use and only use them occasionally. Neither has been dropped or run over either.

The beam type remain accurate for just about forever.