recalibrating a torque wrench

[tie_one_on]

I have a clicker style torque wrench. It's a 1/2" $20 cheapy I bought a few years back. I need to recalibrate it. It's not worth sending to someone to do it. Most places charge $25 or more.<br />My thoughts are to mount the square head into my vise. Set the wrench to a specific spot on the scale, say 30 lbs, use either 30 lbs. of known weights or an analog pull scale set 1 foot from the center of the square wrench head and keep adjusting the wrench until it clicks.(the wrench has a threaded piece to adjust the clicking action). Does this sound right?<br />Also, wrench has a grooved ring around the handle at 15.1875 inches from the head. If I use that as my pulling reference point would I use 23.7 lbs. to make the wrench click if the wrench is set for 30lbs.(30lbs. X (12"/15.1378"))?<br />Thanks.

 

[levittownnick]

Re: recalibrating a torque wrench

I haven't done it but it sounds like a good plan to me. Recheck repeatibility of the adjustment after you try it. I would set the wrench in the vise in a verticle position so that the weight of the wrecch doesn't add or subtract from the reading.<br /><br />When I send my wrenches out they charge $45.00, and if it has a large dial the charge is $170.00.<br /><br />I must send them out because I have a requirement for NIST traceability.

 

[RPJS]

Re: recalibrating a torque wrench

I have done a similar thing to check the accuracy of a torque wrench.<br /><br />If I was recalibarating I would probably use 3 positions either end and in the middle of it's range.<br /><br />Your maths seems right to me.

 

[rottenray6402]

Re: recalibrating a torque wrench

It may be simpler and more accurate to borrow / rent one that reads correctly and tighten a bolt / nut with it to a given value. Then adjust yours upward until it clicks at that value. It may take several times to fine tune it but I think you will be able to get a more accurate reading.

 

[tie_one_on]

Re: recalibrating a torque wrench

Thanks guys.... I thought it would work. Always like a second opinion.

 

[Paul Moir]

Re: recalibrating a torque wrench

I always do mine myself. Figure it's better to test them a couple times a year rather than send them out once every few. I don't use them professionally.<br /><br />There's two ways I do it, depending on the range I'm checking. First, it's absolutely critical that when you mount the wrench in the vice the handle is running precisely level. Second, and this appears to be more important, that the wrench isn't twisted in the slightest. Then do like you're describing above using a string to hang the weights.<br />The other way is for verifying the 100lb setting on my ft/lb torque wrench. I do this while standing on a bathroom type scale and applying force squarely on the marked spot on the wrench's handle with a metal bar. Subtract my indicated weight from the 'click' weight. This actually works very well.<br /><br />Adjustments are usually found behind a rubber plug on the arm of the wrench, or behind a plug at the end of the wrench's handle. It's interesting to find out where your wrench is non-linear. I have a little table of corrections for between 20 and 30 ft/lbs. Any torque under 20ft/lbs is done with my inch/lb reading wrench.<br /><br />Hope those tips help!