I prefer to use a torquewrench whenever possible. Since I don't like spending money, I have bought two of the cheapest quality. (app. 20 Euro each). But to be reasonable sure of the result - I calibrate them - This is how i do:
I use a vise to fix the wrench, a kitchenscale, a container for water, paper and pencil - and a torquewrench
I need to know the load from the container
- and the length from the middle of the handle to the pivot.
- and the load from the wrench itself.
Since I also know the gravity (more or less), I am able to calculate the baseload from the container,
the string and the wrenchhandle:
Using Kg and Meter, and Gravity = 9.82m/sē, the calculation for the baseload is:
(Container + wrench) [Kg] * Wrenchlength [m] * Gravity [m/sē] = Torque [Nm]
I set a rising serie of torques, and pour water (carefully masured) until the wrench clicks.
The torque from the water is:
Water [Kg] * Wrenchlength [m] * Gravity [m/sē] = Torque [Nm]
The resulting torque is the sum of the two torqes abovementioned.
COmparing the torqe set af the scale, with this figure, I get the deviation.
The deviation i surprisingly less than 2Nm, or an max. relative deviation of app. 10% in general +/- 1Nm - not too bad!.
Should you care to se the results (texts in danish):
To achieve app. 80Nm at the larger wrench, some 20 kg is necessary:
- some might add: "Get a life, Stig!"