|
Hi,
Actually, to understand Torque, you need to understand how Threaded Fasteners work.
Nuts, Bolts and Machine Screws work because they are elastic. Tightening them to spec actually stretches them and imparts an Elastic Tension between them, It is this Elastic Tension which keeps them from coming loose. Without it, they would soon loosen due to vibration, changes in temperature (expanding and contracting), etc.
Too much Tension and you will exceed the strength of the Threads, causing them to give way - Strip. Too little tension and the Fastener doesn't stretch sufficiently to hold and will eventually work itself loose. Ever notice that once you bolt something down completely you can still turn it a good ½ to a Full Turn? This is the Fastener stretching.
Using a measuring device such as a Torque Wrench, or a Torque Angle Meter, allows you to control the specific amount of stretch which you impart to the Fastener which is often expressed as Nm or Ft./Lbs.
One more thing about Torque Specs, unless specifically stated, all Torque Specs assume a Dry Thread. Fully 50% of the Torque you apply is necessary to overcome the Friction of the Threads, and this is factored into determining the Torque Spec. Using any kind of Lubricant, ThreadLocker, whether liquid or dry, eliminates this Friction between the Threads. If using any Lubricant or ThreadLocker on a Fastener (unless specifically noted in the Torque Spec), you need to reduce the Torque Spec by 50% (a good Rule of Thumb) to prevent overtightening the Fastener.
Torque Specs on a Wood Screw or Sheet Metal Screw are less important as these primarily use the Friction between the Threads to hold. Hope this helps...
Happy Motoring!... Jim'99
|