This edition of the Fastener Training Minute with Carmen Vertullo was originally published March 15, 2018 as “How to test your torque wrench” during episode 126 of Fully Threaded Radio.
Hi everybody, this is Carmen Vertullo with the Fastener Training Institute coming to you from the Carver FACT Center here in beautiful San Diego, California.
Today, we are going to continue our series of talks on torque wrenches and the use of torque wrenches. I want to give you a kind of a tricky way not to calibrate your torque wrench, but to check out whether or not your torque wrench is accurate. From time to time when I’m doing torque tension testing here or even bolt torquing, something is just not coming out right. And I wonder if the torque wrench is really working the way it’s supposed to. So I have a tricky way of finding this out. You are going to have to put your thinking cap on. It’s going to take a little bit of “Theater of the Mind” action here as I describe to you how to do this trick.
So when we come back you’ll learn how to check your torque wrench for accuracy.
Welcome back everybody to the Fastener Training Minute. This is Carmen Vertullo. We are going to be continuing our series on understanding the use of torque wrenches. And today. I’m going to tell you how to check your torque wrench for accuracy. So I’m going to speak kind of slowly here because I want you to take a minute. You’re going to have to use your imagination as I describe this. It would be nice if we had video but we don’t so here we go. So the object of the game with a torque wrench, of course is to apply a certain torque to the fastener that you’re installing and torque is equal to force times distance. So if you have a torque wrench that’s a foot long for example, and you put 10 pounds of force one foot from the end of it, that’s going to apply 10 foot pounds of torque to that bolt.
So if you can imagine when we put the torque wrench into a calibration machine, that’s what they do. They apply the ten foot pounds and the 20 and the 30 and the 40, and the machine is capable of measuring that. In the lab, that’s how they calibrate it, but we don’t have a lab and we don’t have a machine. So we’re going to do this trick to determine whether or not our torque wrench is functioning properly. So for the sake of this demonstration let’s assume that our torque wrench is a clicker type torque wrench, and we’re going to set it to say 40 foot pounds. It’s a forty foot pound torque wrench, and take that torque wrench, and if you have a bench vise, you’ll need a bench vise to do this. Clamp the end of the torque wrench that would normally go into the socket into the bench vise and arrange it such that the torque wrench is hanging out in midair with nothing below it off the end of the bench. Not on the bench, but off the end of the bench.
Go and find a 5-gallon plastic pail kind of like you would get at the Home Depot. You need to know the weight of that pail and I think they weigh about 1 and 3/4 pounds. So that’s not that important, but good to know. Since all torque wrenches have what’s called an arm or the standard length between the socket and where you would grab it with your hand and apply the force. For a foot pound torque wrench like this one, it’s probably about 18 or 24 inches. Let’s assume it’s 24in. That’s two feet, so let’s set our torque wrench to 20 foot pounds. Then we’re going to hang the bucket on there. And then we’re going to add some weight to the bucket. Now, there’s a couple of ways we can know what the weight is, but we’re all fastener folks. So a good thing we could use for adding the weight is size 1/2 inch hex nuts. I don’t know exactly what a 1/2 inch hex nut weighs, but they all weigh the same. You can go on the IFI Technology Connection and find that out.
And then you’re going to slowly add 1/2 inch hex nuts to the pail until the torque wrench clicks. We Know how much the pail weighs and also we know that torque equals force times distance, Since we have two feet out and are torque wrench is set at 20 foot pounds, there should be 10 lb of weight in the bucket. If we have 10 pounds plus or minus about 5% you know that the torque wrench is functioning properly.
Also, even if you don’t have hex nuts, you could use other things to apply weight. You could use water, since it weighs 10 pounds per gallon, or you could use sand. You just add stuff until the torque wrench clicks. Because we’re all fastener folks, we probably have a precision weighing scale back in the warehouse somewhere. Take that bucket over to the scale and weigh it and do the math. Torque = force times distance. You can do this with indicating torque wrenches. You can do it with large torque wrenches small torque wrenches, you can use a little paint can instead of the Home Depot bucket and so on.
But keep in mind this is not a calibration of your torque wrench. It’s simply a way to check if it’s accurate. If you have any doubts, you should send it out to the lab and have it recalibrated.
Well, I hope you had enough imagination to be able to figure that out. It’s a kind of a fun thing to do. So if you doubt your torque wrench, now you know how to check it out.
This was Carmen Vertullo for the Fastener Training Minute and the Fastener Training Institute. Thanks for listening.