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Originally Posted by Kevin Horton
Sorry Frank, but you need to go back to physics class.
CASE 1 - extension in line with torque wrench
Let's assume you have your torque wrench set to 100 in-lb. Let's assume the distance between the hand grip and the square drive for the socket is 10 inches. If you put a socket on the wrench, and put it on a nut, you'll need to pull on the hand grip with a force of 10 lb to create a moment (torque) of 100 in-lb.
Now, let's imagine that you have an extension that is two inches long. You mount the extension so that it is aligned with the axis of the torque wrench, so the end of the extension is now 12 inches from the hand grip on the wrench. You put a socket on the extension, put it on a nut, and pull until the torque wrench clicks at 100 in-lb. How much torque have you put on the nut? The torque on the nut is the sum of two things:
1. The torque wrench applied a moment of 100 in-lb to the extension, and this moment is reacted at the nut.
2. You pulled on the torque wrench hand grip with a force of 10 lb, and this force is reacted where the torque wrench is attached to the extension. The 10 lb of force on the end of the extension creates a torque at the nut of 10 lb x 2 inches = 20 in-lb.
The total torque applied to the nut = the sum of 100 + 20 = 120 in-lb.
CASE 2 - extension at 90 deg to torque wrench
The 10 inch long torque wrench is still set to 100 in-lb. But now the 2 inch long extension is at 90 degrees to the torque wrench axis. We put a socket on the extension, put it on a nut, and pull until the torque wrench clicks at 100 in-lb. How much torque have you put on the nut? The torque on the nut is the sum of two things:
1. The torque wrench applied a moment of 100 in-lb to the extension, and this moment is reacted at the nut.
2. You pulled on the torque wrench hand grip with a force of 10 lb, and this force is reacted where the torque wrench is attached to the extension. This force is transferred through extension, and is reacted at the nut. How much torque does this force create at the nut? Well, the force is actually aligned with the axis of the extension. This is just like putting a wrench on a nut, and then pushing on the end of the wrench so that the direction of the push is directly towards the nut. You can push as hard as you want, and the nut won't turn, as the axis of the force is directly through the nut. The distance between the axis of this force and the centre of the nut is 0 inches, so the torque = 10 lb x 0 inches = 0 in-lb.
The total torque applied to the nut = the sum of 100 + 0 = 100 in-lb.
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Actually I took about 10 mins sketching this out and decided indeed its not just the torque but also the force applied and the reaction therof.
The reason the extension can be ignored of course is that the effective is not the hypotenuse of the angle becuse the force is at 90 degrees to the torque wrench
It was not obvious though....Yup too long out of school
In short keep yer torque wrench aligned with the extension an use Dan's calculator...
Frank
Linear Mode
