How accurate is your torque wrench?

[Steve83]

Everyone knows that click-type wrenches have to be stored at their LOWEST settings (or just below), right? If you throw it in the toolbox at a high setting, it won't work next time you try to use it.

 

[waiting for time]

Anyone ever concidered how acurate torque is?
If you look at how much of the applied torque is converted to clamping force (kN) it is scary.
Only about 8 to 12% is converted to pre-load or clamp force.
When 10 nuts are tightened using the same wrench and the same torque value the difference in clamp force runs up to 40%. If the same 10 bolts are placed in one connection the difference can run up to over 70%.
Looking at the cheap devices that are used to calibrate the wrenches, you might want to calibrate them before drawing any conclusions from their measurements. They are often even more off as the wrenches.
We actualy calibrate the inustrial devices that are used to calibrate torque wrenches and research the actual quality of critical bolted connections and let me tell you, you do not want to live next to a wind turbine.

 

[Dragos80]

Harbor Freight moving upscale.

Just found it on youtube.

 

[toyotaspeed90]

I personally don't care how accurate they are. For me, there are some older versions of an engine (4age) that use specific torque values on the headbolts that I've cared about, and on con rods/mains - yet oddly the same engine in later 'versions' use a TTY setting instead for the heads.

Just about everything else I don't bother as I haven't seen a need to. That might, in part, be ingrained in me due to a discussion I had with my father probably over a decade ago from his experiences in the past.

He was an engineer (then manager of the engineers... that sounds awful) for a company that designed and built medical equipment - especially equipment focused on premature babies.

Everything the company produced had to be FDA approved - which includes even the calibration/use of torque wrenches. The wrenches used in their assembly were extremely expensive (somewhere in the range nearing $1k/ea) and they had to be calibrated routinely (I believe every 6 months). If not, they didn't meet FDA approval.

Someone else mentioned this - and what I find more important is consistency. I've found different ways to use my tools in a way that are consistent. If I'm bolting on an intake manifold, I make sure the bolts are tight, and even. (I've gone through in the past and double checked with torque wrenches and found that I tend to be more consistent than the torque wrenches).