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Old 04-18-2008, 02:43 PM
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Technical question: MATH PHYSICS PLEASE

Ok guys, I can't find/afford a torqu wrench to tight down that 350 Lb/Ft pitman arm nut. SO I came up with a decent "idea". I have a very nice 200 Lb/Ft click type torque wrench. My idea is to fab up an extender.... as in take a say 3' long pipe and weld a socket/1/2" male end on the ends of the pipe and then torque the end of it to say... 150Lb/Ft. I wish I could draw a picture. the Physics guys know what i'm talking about. It's apply torque to a bar already on the nut. It multiplies your torque and with a equation you can calculate how long the bar needs to be, or how much torque you need to get your end/net torque. Need some help with the Calculation. b/c if you apply say 50 Lb/ft of torque to a 1' bar, How can it still be 50? But if the bar is 2' long your torque should be 100#?
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Old 04-18-2008, 02:58 PM
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I can probably help you out but I don't understand exactly what you need? The equation is applied force times cross distance. Meaning that if you apply 100 lbs at the nut it is a 100 lbs of force then if you apply the same force on the same nut with a 3ft long wrench then it has a moment of 300lbs/ft
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Old 04-18-2008, 03:01 PM
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The reason it can be 50 ft/lbs no matter the length of the bar is because of the internal components of the wrench. No matter how long of an extension you put on the torque wrench it is still going to break loose at 50lbs/ft. If you put a longer bar on the wrench it is just means it will take you less applied force to reach the breaking loose point of the torque wrench.
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Old 04-18-2008, 03:02 PM
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Yes, I understand the basic equation of Lb/Ft. If you apply 100# perpendicular to a 1' bar on a nut, you have 100 Lb/Ft acting on the nut. Now, what I'm asking is, what if you set your torque wrench to say 100 Lb/Ft and torque a 1' bar on a nut? In other words your putting your 100 Lb/Ft torque wrench on the END of a 1' bar on a nut. No way it can be 100 Lb/Ft if you extended the point 1'. Only thing I came up with is you add the 1 foot built into the wrench. so that 1' you are torquing, becomes 2' with 100# meaning you have 200 Lb/Ft of torque on the nut. Am I correct or not?
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Old 04-18-2008, 03:05 PM
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Here is an idea take a 1/2 inch breaker bar and use a 3 ft piece of pipe for extra leverage and tighten that nut until you can no longer physically turn it. I have done this many times when putting lifts on trucks. After a week go back and recheck the nut I gaurentee it will not have came loose.
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Old 04-18-2008, 03:05 PM
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I understand what youre saying now. I guess it should tighten it by however much more longer the bar is. Sounds like it could work? Try tightening down the bolts to the maximum torque of the wrench then adding the extension bar you are talking about and tightening it again. If it tightens more then it works.
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Old 04-18-2008, 03:09 PM
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I think I figured it out. If you are putting your torque wrench on the end of a 1' bar on a nut... and your wrench is set to say 30 LB/Ft, you're not taking into consideration the 1' built into the wrench's calibration. So if you torque 30 Lb/Ft on a 1' bar on a nut, then it's really a 2' x 30# equation meaning you have 60 Lb/Ft acting on the nut. Has to be... b/c with a 1' bar, the Lb/ft math doesn't make sense. But if you add 1' it does which you don't see b/c it's "in the wrench".

I drew it out by vectors and it works. you have to add the 1' that the wrench is "calibrating" into it. Once you draw it out, pictorally/vectors it makes sense. so if I have a 2' bar, and my wrench is set to 50#, it's 3' x 50# yielding 150 Lb/Ft on the nut.

Last edited by JBakerFX4; 04-18-2008 at 03:14 PM.
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Old 04-18-2008, 07:15 PM
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I would advise not doing that.... yes you can add torque to the wrench by extending the bar to gain leverage. all you are going to do is make it easier to reach the 250 ft pound mark. You are still going to "over exert" the wrench and throw it out of calibration if not damage the wrench.
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Old 04-18-2008, 08:49 PM
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I agree with bigcountrysg, you are making this way more complicated than it needs to be.
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Old 04-18-2008, 09:10 PM
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Quote:
Originally Posted by Echo View Post
I agree with bigcountrysg, you are making this way more complicated than it needs to be.
Yes he is.

What your going to do is allow you to apply more force with less work. The longer the handle the more leverage you get. But that does not mean you will apply more torque to the nut. The more leverage means less amount of work is needed to gain the same force.

Last edited by bigcountrysg; 04-18-2008 at 09:15 PM.
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