The essential torque wrench best practice guide

The essential torque wrench best practice guide

qldcalibrations AdminSep 2, '19

Whether you're an experienced torque wrench user or if you have never worked with a torque wrench before, this guide can be used as a quick refresher or an introduction to make sure you are getting the most out of your tool for best torque wrench performance.

A torque wrench is designed for accuracy - but it needs your help!

Let's start with the basics of a torque wrench.  A torque wrench is essentially designed for accuracy and precision to avoid under tightening and over tightening in order to meet very specific fastener requirements.  Under tightening can lead to an ineffective, and even dangerous situation - while over tightening can lead to breakage.

Usually in the form of a socket wrench, a torque wrench is a tool that applies set specific force to a fastener.  This specific force is known as 'torque' and is vital for automotive and mechanical jobs that require an exact tightness of screws and bolts.

Torque wrench effectiveness is only going to be as good as the user's working knowledge, resulting confidence and performance considerations of the tool.

Before you start, get to know your torque wrench...

Before you put your torque wrench to work, it is vital that you and your co-workers understand how the tool works from the moment it is taken out of the box.

Here at Queensland Calibrations, we highly recommend that you give your torque wrench a practice run before taking it in for a full day of work.

Following the seven simple steps listed below will give you the understanding and confidence to be an effective tool user - improving your overall speed and sustainability of your work when the time comes to get the job done!

  1. Open the wrench box and check the Certificate of Calibration.  Also inside the box, you will find the instruction sheet.  Take the time to carefully review these documents to ensure the calibration is up-to-date and that the instructions make sense to you and that you are confident to proceed with the next steps.
  2. Take the time to visually inspect the wrench to ensure there is no damage (such as cracks or worn parts of the tool).  If the torque wrench looks as though it is in good condition, you can proceed to unlock the wrench.
  3. Refer to the handbook to locate the exact torque setting required for the job.
  4. Set the wrench (always approaching from a lower torque) and lock the chosen setting.  Keep in mind not to set the wrench beyond the scale.
  5. With your hand, check that the ratchet is moving in the required rotational direction.
  6. Time to fit the appropriate extension and socket.
  7. Connect the torque wrench to the fastener.  Grip the centre of the handle (and do not grip at the ratchet end).  Tighten the fastener in a smooth downward action.  Stop when you hear and feel the torque wrench click.  One click is enough for accurate results.

Tips for torque wrench safety, performance and longevity...

  • Your protection should always be the number one focus - For your safety, always wear appropriate eye protection and work gloves when operating a torque wrench.  It's also advisable to check your torque wrench's integrity every time before use.
  • Consider the working environment - A torque wrench should not be underwater in any circumstances as the tool will rust.
  • Tool use - Apply torque in a slow and careful manner and avoid sudden movements.  Always be delicate with a torque wrench so accuracy of the instrument is not disrupted.  Do not use any accessories or extensions unless specifically mentioned that they are allowed by the torque wrench manufacturer.  It is also not recommended to use a hammer with a torque wrench.
  • Torque wrench storage - When not in use, keep the torque wrench in the box the tool came in to protect it from dust and coming into contact with other tools.  The box should be secured with low humidity and consistent temperatures.
  • Regular calibration of your torque wrench - The only way to be sure a torque wrench is accurate, consistent and repeatable is to periodically validate its performance.  According to ISO Standards, torque wrenches should be calibrated every year (or every 5,000 operations - whichever come first) as it has been found that torque wrenches can fall up to 10% out of calibration in the first year of use.  Do not use a torque wrench if you are unsure of the last calibration.  Also - if you suspect the wrench has been dropped, have the tool inspected immediately to ensure proper calibration. 

Frequently asked questions (and answers) about torque wrenches...

  • What does the torque wrench click mean? A click means that you have applied the torque to the fastener as it has been set to the wrench (only one click is required). Further clicks will result in over torquing the fastener.
  • What is the difference between an impact wrench and torque wrench? An impact wrench is a tool that will tighten a fastener - however, it is not controlled in terms of torque and therefore does not operate in the same fashion as a torque wrench.
  • What size sockets can a torque wrench be used on? A torque wrench will fit any sockets that can connect to it using the square drive. Torque wrenches have different square drives. For example, the smallest torque value Norbar wrenches have is a 1/4 inch square drive, moving through to a 3/8 inch square drive - and all the way to a 1/2 inch square drive for the largest torque wrenches.
  • Will a change in socket size effect accuracy? A change of socket size will not affect the torque accuracy. The distance is measured from the rotational axis and this remains consistent - no matter which size of socket is used on the fastening.
  • How will a socket extension affect a torque wrench? A socket extension will not affect the wrench as it won't alter the length of the wrench. According to Norbar, if a wrench extension is being considered, the following formula will calculate the effect of a torque wrench extension: M2 = M1 x L2/L1 where L1 is the normal length, L2 is the extended length, M1 is the set torque and M2 is the actual torque applied to the fastener.
  • Do I need to unwind the torque wrench between uses? When a torque wrench is in regular use it does not need to be wound back.  However, when storing a torque wrench for an extended period of time, Norbar Australia strongly recommends unwinding a torque wrench to its minimum setting (never to zero), and therefore relaxing the springs after use. 

Pub trivia - Origin of the torque wrench...

The torque wrench was first patented in 1931 by John H. Sharp (USA) who originally referred to the tool as a 'torque measuring wrench.'

However, Conrad Bar claimed he first invented a torque limiting tool in 1918 to alleviate the problems he was having in his workplace - the inconsistent tightness of bolts.

In 1935, Conrad Bar and his business partner George Pfefferle patented an adjustable ratcheting torque wrench. This tool in 1935 featured audible feedback and restriction of back-ratcheting movement when the desired torque was reached.

The next steps...

We trust this guide was a useful starting point or a good refresher for you to confidently and effectively use a torque wrench at best practice level.

For more information and guidance about your torque wrench, we encourage you to always read the paperwork that comes from the wrench's manufacturer.

If you'd like to know more about purchasing a torque wrench or calibration to achieve sustained best performance, please contact us here at Queensland Calibrations. We are happy to help you achieve best practice results with your torque wrench.