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Torque Wrench:

 
 
 

A torque wrench is a precision measuring instrument. It measures the force required to turn a nut or bolt. Many different styles and sizes of torque wrenches are available. This information will pertain to the common hand held torque wrench. Torque wrenches

Top down (1/2" drive reversible ratchet head, 3/8" drive fixed head, 1/4" drive Beam Type) They consists of only a few parts. The head, beam, lock ring, grip, and a blade. They should be maintained and calibrated per the manufactures instructions.

The torque settings are stamped into the beam. On the Beam Type wrench a scale is attached to the beam. The increments can vary from inch pounds (CM-KGS) to foot pounds (NM) depending on the size of the wrench.Torque wrench scale

On the barrel type wrench you preset the torque you want by releasing the lock ring and rotating the grip to the specific value. Once that value is reached the torque wrench will over center and "click". Informing you that the bolt or nut has reached your preset value. Remove the wrench and move to the next one. It's that simple to operate

.Torque wrench beam scale

With the Beam Type wrench you have to pull or push the handle and watch for the needle deflection. There's no tell tale "Click". 
The torque wrench is calibrated from the center point of the drive to the center of the grip. While holding the wrench by the grip only you should apply a slow and steady force in the direction you're tightening. Sometimes two hands are needed for heavy torque values. Place one on the grip and the other on top of the head. Never grab the wrench in any other place. Hand position
Hand position 

Some times it might be necessary to hold the head steady. Just apply enough downward pressure on the head to keep the socket steady.

You should never leave a torque wrench preset to any value other than zero when not in use. (Avoid premature and accuracy failure)

When the scale on the wrench is not in the increment you need, you can calculate the equivalent.

In-lbs to Ft-lbs (In-lbs / 12= Ft-lbs)

In-lbs to Cm-kgs (In-lbs x 1.152=Cm-kgs)

In-lbs to Nm (In-lbs x .1130=NM)

Ft-lbs to In-lbs (Ft-lbs x 12= In-lbs)

Ft-lbs to Cm-kgs (Ft-lbs x 13.83=Cm-kgs)

Ft-lbs to NM (Ft-lbs x 1.356=NM)

Cm-kgs to In-lbs (Cm-kgs x .8680=In-lbs)

Cm-kgs to Ft-lbs (Cm-kgs x .07233=Ft-lbs)

Cm-kgs to NM (Cm-kgs x .09806=NM)

NM to In-lbs (NM x 8.851=In-lbs)

NM to Ft-lbs (NM x .7376=Ft-lbs)

NM to Cm-kgs (NM x 10.20=Cm-kgs)

 

In places where access to the nut or bolt are limited you might need an adapter.

This changes the torque value since you're changing the length and or angle of the wrench.

The corrected values can be calculated. That's right more math! Really hard math!

Torque wrench adapter 
Example I Image drawing Inline adapter

T1 = (TA)/(A+B)

A = Torque wrench length

B = Adapter length

T = Actual torque value

T1 = Corrected torque value

41.25 ftlbs=(55 ftlbsx18")/(18"+6") 

Example II Image drawing

Using a handle extension no correction needed

Example III Image drawing Inline Adapter with extension T1 = (TA) / (A+B)
Example IV Image drawing Both handle and adapter T1 = (TA) / (A+B)
Example V Image drawing An angle other than 90 degrees. "B" should never exceed the length of "A". This example should be avoided when every possible.

T1 = (TA)/(A+B)

A = Torque wrench length

B = Adapter length

T = Actual torque value

T1 = Corrected torque value 

It's recommended that a stirrup-type handle with a pointer indicating angle of loading be used to ensure the correct angle.

Example VI

Image drawing

No correction needed

You are now ready to tighten up the world!
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