Heard from a friend (who used to work as mechanic helicopters) that there is such thing as a torque tool calibrator.

I was all bragging out the wonders of spending good cash for a Craftsman torque tool. When he asked, How are you sure it is giving proper readings.

I ask, Has anyone heard / used such device?

Went on a mission trying to find one and it seems the mechanical ones are no longer sold and if so for an arm and a leg compared to before. The current ones are digital and are in the 2 grand range.

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Well like any measuring tool, which the torque wrench is of sorts, it needs to be calibrated. The problem myself and others have had with the twisting handle version, is that once you set it to a torque, you can move the labeled handle so it reads anything. That's how they calibrate it. They'll set it to a random torque, let's say 60ft/lbs. They verify that it's at 60ft/lbs, and/or tweak it until it is. Then they move the handle until it actually reads 60ft/lbs.

I don't think the calibrating tool is something you buy, but I know there are a number of places that you can send tools in, like micrometers, calipers, torque wrenches, thread gauges, etc., to be calibrated.

If you can find one of these:

You can measure your twist handle one against it, and see if your twist handle torque wrench is reading correctly. That's the down and dirty version, and cheaper if you think you'll be throwing your torque wrench out of whack often.

 

I have a proto 50-250 ft/lb 1/2" drive that was last calibrated in 1990.

 

I've got a snap on 15-100+ from when I build Subaru motors. Works great and I've spent enough time wrenching I can ballpark 45ft/lbs. Still use the gauge tho

 

I did torque wrench calibrations during my apprenticeship (they have a certified metrology lab), the machines you use to do it aren't something you'd buy for yourself (plus they need calibration too).

Send your torque wrench out for calibration as suggested above.

 

Or just use one of these in the first place and get bitches.

 

That style have to be calibrated too... ALL torque measuring tools have to be.

 

At its very simplest, a torque wrench calibrator isn't very complicated. You could make one using a bench vise, a massless lever of a known length, a reference object of a known weight, and a bit of twine.

In practice, torque wrench calibrating machines are hideously expensive. Here's a "basic" model that sells for $20,000: http://www.grainger.com/Grainger/CDI...4&ci_sku=5PVG7

As others have said, you can of course send your wrenches out for calibration. A lot of big companies have their own cal labs (I get my personal scopes and meters done free through Harris) but there are also shops that anybody can send a tool to for calibration.

Or you could just say "you know what, this isn't a spacecraft I'm working on here, it's an engine block which was made 20 years ago from cast iron. Are the consequences of my torque wrench being out of calibration by 10 or 20% likely to be all that serious in the grand scheme of things?"

 

I worked in a military calibration center for a while and found that by far the simple bending beam torque wrenches were the most accurate and reliable, providing you use them properly. The twisty handle ones were the worst for accuracy but relatively easy to calibrate and the dial gauge ones were worse to calibrate but maintained their calibration much better. The digital snap-on ones were pretty good too.

This is what we used to calibrate medium sized torque wrenches.
http://buy1.snapon.com/catalog/item....re&dir=catalog
http://buy1.snapon.com/catalog/item....re&dir=catalog

We also had a separate tester for 250-1000ft-lbs and one for tiny wrenches as well.

 

I'm really curious to know how well calibrated the torque wrenches that folks at our end of the scale (Craftsman, Kobalt, Harbor Freight, etc) are out of the box. I've been googling around for a while, and I can't find any serious data on the subject.

 

I work at a military metrology lab and as stated, the torque testers and transducers are extremely expensive.

Joe, from what I've seen, the Craftsman level wrenches are typically ± 4% to 6% CW and ± 6% CCW out of the box. Usually a new wrench will meet those specifications. Depending on how much they're used they can hold that specification for a while, but if they see any regular kind of use they'll exceed those specifications within a few months.

You can get nicer wrenches like those from CDi that will come new at a 3% or even 2% spec but they'll have to be certified at 4% or worse after a few calibration cycles due to nonlinearity across the range.

Deflecting beam wrenches are awesome, dial ones are a pain to adjust but also hold their cal very well.

 

This is the theory I subscribe to.

 

I checked my (at that time) 3-4 year old Craftsman 10-75lb-ft torque wrench when I worked in the metrology lab during my apprenticeship, was within the +/-4% across the range.

 

Look up GRM's article too, they tested a number of used/new/cheap/expensive torque wrenches, with some interesting results.

 

BTDT. My wrench read about 8% low.

 

I actually have access to a torque tool calibrator here at work. We have a metrology lab and calibrate all sorts of stuff, torque wrenches, accelerometers, displacement devices, load cells etc. The torque wrench calibration tool is quite large and weighs several hundred pounds, not exactly something most people would have.

FWIW I trust the bendy beam style wrenches to stay consistent and repeatable much more than the clicker types.

Bob