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Torque Wrench Extension – Increase Measurable Torque

Background on Torque Wrench Extensions

Many of us Do-It-Yourself guys do not have a torque wrench that will go up to 600 pounds, so what do you do if you need to accurately tighten a bolt to those specifications?  Rather than spend $400 plus on a new torque wrench, you can easily make one for around $25.  In the video above you can see how we had one made to work with just about any situation we could run across.

How Toque Wrench Extensions Work

Torque Wrench Extension

 

The Torque Wrench Extension shown here increases the effective length of the torque wrench.  When you do that, the amount of  torque applied to the bolt becomes higher than the setting on the torque wrench.  It’s the same thing with a breaker bar, the longer they are, the easier it is to apply the force needed to remove a nut.

When you use a Torque Wrench Extension, there is a formula to account for the length of the extension and to calculate the setting that you choose on your torque wrench.  The formula is as follows:

 Desired Torque x Wrench Length / (Wrench Length + Extension Length)= Wrench Setting

 To help make this clear, let’s go over an example.  We have a torque wrench with a length of 24 inches, and the length of the extension is 12 inches.  We need to tighten a nut to 450 ft-lbs, so our desired torque is 450 ft-lbs.

Wrench setting = 450 x 24 / (24 + 12)

                            = 10,800 / 36

                            = 300 ft-lbs.

In this case, when the torque wrench is set to 300 ft-lbs, the actual torque applied to the nut will be 450 ft-lbs.  You can also use our online calculation:  Torque Wrench Extension Formula

How to make a Torque Wrench Extension

Torque Wrench Extension BuildOur goal in making the extension was to make one that could be used in many different situations and was not just for one specific task.  We called our local metal shop and had them broach square holes two inches apart in a piece of 1/2″ steel that was 3″ wide and 40″ long.  This would allow us to put the torque wrench at any position along the bar in order to accommodate many different higher torque values.  To make it simple, just weld a cut up 3/4 extension to one end for the socket to connect to, making sure its 90 degrees to the bar.

In the video above, we used our 3/4″ torque wrench and our larger adapter.  That adapter can be used in many ways and we used a 3/4″ square plug to connect the socket.  When using that at 900 ft-lbs, we twisted it pretty good and decided to weld on a store bought extension.

Safety First

When tightening bolts up to high values, make sure the bolt you are using can handle the torque.  In most cases, once some of these bolts have been torqued to these high values, they are not to be used again.  Bolts in some ways will stretch and be like a spring at max torque values.  Make sure that you are prepared to get out of the way if something were to break.

We can help with questions!

Our forum is full of very intelligent people who are more than willing to help you with your projects.  Take a look at our forums, sign up and start posting and asking questions.  Workshop Addict Forums

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4 Responses to “Torque Wrench Extension – Increase Measurable Torque”

  1. Ray Schwabe #

    Where did you find (purchase) a 1/2″ to 1/2″ square plug to fit the torque wrench extension project. They all seem to be reducers or step downs. Or did you use a simple steel plug. Most likely that would not be strong enough.

    June 30, 2019 at 2:00 pm Reply
    • We made it.

      September 24, 2019 at 8:05 am Reply
  2. Przemek #

    When on the wrench you set up 300nm this is maximum torch power,when you extending the key doesnt help because key is set up for 300nm

    July 20, 2019 at 6:22 am Reply

Trackbacks/Pingbacks

  1. Milwaukee M18 FUEL 3/4″ Impact Wrench Review 2764-22 | Workshop Addict - Wood & Metal Forum - March 10, 2015

    […] we broke out a 3 foot long 3/4″ torque wrench capable of 600 ft-lbs and connected it to our Torque Wrench Extension (Follow Link) and calculated 1,200 ft-lbs.  With a 3 foot breaker bar on the bolt and a 5 foot […]

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