Improvise a torque wrench with a luggage scale
If you don't have a torque wrench available - or if you want to check the readings of the one you have - it is easy to improvise by using a standard wrench and a scale as indicated in the figure above.
The moment - or torque - can be calculated
T = F a (1)
T = moment or torque (Nm, lbf ft)
F = applied force (N, lbf)
a = length of the wrench (m, ft)
Note! - Most scales in the SI unit system measures weight - force due to the acceleration of gravity - in kg.
- the difference between mass and weight.
The reading from the scale can be converted to N by using
F = m g
m = reading of the scale (kg, lbf)
g = acceleration of gravity (9.81 m/s2, 32.17 ft/s2)
Example - Measuring Torque with a standard Wrench and a Luggage Scale - readings in kg
The reading of the scale at the end of the wrench is 10 kg. The length of the wrench is 0.3 m. The moment exerted can be calculated
T = (10 kg) (9.81 m/s2) (0.3 m)
= 29.4 Nm
Example - Measuring Torque with a standard Wrench and a Luggage Scale - readings in lbf
The reading of the scale at the end of the wrench is 20 lbf. The length of the wrench is 6 in. The moment exerted can be calculated
T = (20 lbf) (6 in)
= 120 in lbf
= 10 lbf ft
"Luggage Weight - Wrench" Online Torque Calculator
Scale Wrench Torque Diagram - SI units
Example - Torque Settings for a Cylinder Head
The torque settings for a cylinder head in a car engine are specified to 30 Nm.
According to the diagram above with a wrench with length 0.2 m - the scale readings should be approximately
Scale Wrench Torque Diagram - Imperial units