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# Improvised Torque Wrench

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)

where

T = moment or torque (Nm, lb f ft)

F = applied force (N, lb f )

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 reading from the scale can be converted to N by using

F = m g

where

m = reading of the scale (kg, lb f )

g = acceleration of gravity (9.81 m/s 2 , 32.17 ft/s 2 )

### 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/s 2 ) (0.3 m)

= 29.4 Nm

### Example - Measuring Torque with a standard Wrench and a Luggage Scale - readings in lb f

The reading of the scale at the end of the wrench is 20 lb f . The length of the wrench is 6 in . The moment exerted can be calculated

T = (20 lb f ) (6 in)

= 120 in lb f

= 10 lb f ft

### 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

14 kg

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