29-06-2018, 06:42 AM
Torque wrenches are useful when working in awkward positions. Whilst an appropraite pressure can often be judged at a bench lying under a car can be different. The simple pointer type also then sometimes awkward although otherwise fine.
Machinerys Handbook gives the accuracy of applied tension as + or - 25%!!. By hand (presumbaly an experienced operator) + - 35%. it is generally reckoned even very experienced workers tend to overtighten small threads and under tighten large.
The thread is not reckoned to make much difference except as it affects the core size.
Only a fraction of the torque contributes directly to tension; most is friction. For the same total tension producing same joint compression, torque increases more or less in proportion to dia.
Decades ago when tools were expensive, for use on family moderns my father and self made wrenches out of 1/2 inch HT rod and filed Seven axle bits.
Machinerys Handbook gives the accuracy of applied tension as + or - 25%!!. By hand (presumbaly an experienced operator) + - 35%. it is generally reckoned even very experienced workers tend to overtighten small threads and under tighten large.
The thread is not reckoned to make much difference except as it affects the core size.
Only a fraction of the torque contributes directly to tension; most is friction. For the same total tension producing same joint compression, torque increases more or less in proportion to dia.
Decades ago when tools were expensive, for use on family moderns my father and self made wrenches out of 1/2 inch HT rod and filed Seven axle bits.