FTM122: Torque Wrenching, Part 1

If I use an extension with a torque wrench, does that modify the torque value or change the result that I'll get using that torque wrench?

This edition of the Fastener Training Minute with Carmen Vertullo was originally published November 20, 2017 as “will using an extension change the torque reading” during episode 122 of Fully Threaded Radio.

Well, Hi everybody, this is Carmen Vertullo with the Fastener Training Minute brought to you by the Fastener Training Institute and I’m talking to you from the Carver FACT Center. FACT stands for Fastening Applications Consulting and Training and that is what we do here at our place in San Diego, California.

I recently had a question from a client regarding the use of a torque wrench. The client was a fastener supplier and they got the question from their customer who is using fasteners, and the the question was this: if I use an extension with a torque wrench, does that modify the torque value or change the result that I’ll get using that torque wrench? It’s a very good question and it has two answers when we return. I’ll tell you what they are.

Back to the Fastener Training Minute. This is Carmen Vertullo talking to you today about torque wrench use.

Now the question that I received had to do with the use of an extension on a torque wrench. Now, I’m going to have to ask you to use your imagination here. I wish we had a screen to show you but we don’t so just think about using a typical ratchet with an extension and a socket, and the extension comes directly out of the square Drive of the ratchet goes on to the socket in the socket goes on to the Fastener. Everything lines up. Now torque is equal to force times distance (T = F x D). So when we apply torque to a fastener the distance between where the fastener is and where our hand is on the tool is the distance. So let’s say that tool’s ratchet was 1 foot long and then we’re going to apply 50 pounds of force at that place where our hand is on the tool.

That equals 50 foot pounds of torque, it’s that simple. Now a torque wrench works the same way as a ratchet except it has a control device in it to help us control the torque. The most common type of torque wrench is called a clicker, and when we reach the torque that’s set in the tool the wrench kind of slips a little bit and gives us a click tat lets us know where to stop. So the question is, when I put that extension on that torque wrench like I would on a ratchet does it affect a torque value? Well, think about that does the distance between the Fastener and where your hand touches that wrench or applies to force change? In this case, it does not. So the answer is that as long as you keep that extension straight up and down between the output of the torque wrench and where the socket attaches to the fastener, you will not affect the application of torque through the torque wrench.

Now there’s another type of extension sometimes that is sometimes used on a torque wrench. These extensions are called crow’s feet or dog bones, and they actually do affect the length of that torque wrench in the torque equals force times distance equation.

Next time on the Fastener Training Minute I will tell you how to deal with changing the torque value in a torque wrench when we have an extension that changes the length of distance in the torque equals force times distance equation.

Well now, you know something about torque wrench use that you didn’t know before. This has been Carmen Vertullo with the Fastener Training Minute. Thanks for listening.

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