Torque wrench extention question
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  1. #1
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    Default Torque wrench extention question

    I need to torque some bolts in a spot thats too small for a torque wrench head. I can reach them with an 2 1/2" extension. By this I mean something to give the wrench more lenght, not a regular socket extension. I have a click type torque wrench. There is a formula to figure the correct torque when using an extention with a wrench that has a fulcrum pin in the handel. I read that it wont work with a click type because they lack this pin. Wouid the torque setting on the click type wrench be reasonable accurate if the extention was set at 90* to the handle there by not adding much lenght? Or should I buy the pin type wrench?

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    I think you can use what you have. All your doing is changing the ratio of leverage.

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    Torque is measured at the socket axis. It does not depend on the length of the wrench handle. That only affects the amount of pressure you have to exert to achieve a particular torque.

    For example, if you want 24 inch-pounds, you must apply 2 pounds of force with a 12" handle but only one pound of force on a 24" handle. The clicker will open at the preset torque regardless of the amount of pressure you apply to the handle.

    - Leigh

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    There is a formula and I have used it when grafting a box wrench to the end of my torque wrench in order to reach difficult fasteners. It is shown in my users manual.

    T(W)= T(E)L/L+E T(E)= T(W)L+E/L

    E-Effective length of extension measured between centers(torque wrench and extension)

    L-Lever length of the torque wrench (center of grip to the center of drive)

    T(W)-Torque set on the wrench

    T(E)- Torque applied by the extension to the fastener

    Draw yourself a diagram and it will become clear to you.

    Norb

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    Mudflap. That will work fine with a pin type wrench. The center of the handle is the point where the force is centered. Just where that is hard to say without the fulcrum pin. It depends on how the handel is pulled. The wrench I have has a pivot pin about 2' back from the drive square. This is where it 'clicks'. Im not sure how that may factor into the equation.

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    Danny,

    These instructions are for an old click type torque wrench much as you describe, Craftsman Microtorque to be extact.

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    If you look at the equations as a means of compensating the value of T(W) in order to arrive at a correct T(E) it becomes much simpler.

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    When you say "click" I assume that means when the proper torque is reached then the wrench "breaks" (not a beam type).

    In this case pull on it anywhere you want to , with a 10 foot cheater or choke up on the wrench. Just stop pulling when you hear the "click" like Carl and Leigh say.

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    The calculation is the same for all types of torque wrenches. The pin position is only taken into consideration when calculating the forces within the wrench itself. All you need to know is your overall lever length, and how much pull you are putting on the end, to get your torque at the fastener. The torque wrench tells you how hard you are pulling at the handle when you back out the ft/lbs, the formula tells you how much torque is on the fastener when you make the wrench show that many foot lbs. Picture a bending beam type torque wrench - how would you calculate that formula if you needed to know where the pin was? Here's a calculator showing a dial type wrench(my favorite) - the calculation is the same - http://www.belknaptools.com/extcalc.asp

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    Here's an interesting treatise on how where you pull on a click type wrench can affect the torque applied when it clicks - http://www.sacskyranch.com/torquew.htm

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    There is a formula to figure the correct torque when using an extention with a wrench that has a fulcrum pin in the handel.
    Oh, I understand what you are asking now. The pivoting handle is not absolutely necessary, but you do need to be careful how you pull on the handle. You need to pull at 90° to the wrench, and have your hand centered on the grip, simulating the effect of the pivot as well as possible.

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    Interesting. It makes intuitive sense to me that vertical, horizontal and twist would affect the readings.

    However, in the example given, I don't see why the click type was being significantly affected by where on the knurled grip zone you grab it. 1-2% maybe but 8% error range like in the example? This was for about 8.3 ft/lbs but still. Maybe someone can explain what is actually happening to make a clicker so sensitive. Maybe it less of an issue in 1/2" drive clickers putting on lugnuts

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    Quote Originally Posted by Danny D View Post
    The wrench I have has a pivot pin about 2' back from the drive square. This is where it 'clicks'.
    Maybe this is something new to me and why I may have missed something here.

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    Danny,

    You're not asking about putting an extension on the finger handle end of the wrench, right?

    What you need is an extension on the drive square BOLT end of your clicker wrench, right?

    -Bruce

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    With a click type wrench I think you could choke up on it or add a cheater bar and get an accurate torque. I read that if an extension is added readings could be up to 20* off depending how it was pulled because of the lenght issue. If the extension was set at 90* to the handle thereby not adding lenght would the setting on the wrench be the same as the torque on the bolt? By the way I am needing 180 inch pounds on the bolt. The extension would go on the drive square end.

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    Preset torque wrenches are designed to give consistent results, within a reasonable tolerance, despite variations in manner of use. That's why they're sold in the first place. This is their advantage over the "long needle" type of wrench.

    If you're working with a quality product, an extension of the handle is of absolutely no consequence. If you're using a chink POS, then you won't get consistent results under any circumstances.

    - Leigh

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    Wouid the torque setting on the click type wrench be reasonable accurate if the extention was set at 90* to the handle there by not adding much lenght?
    The short answer is yes. If the distance from the midpoint of the grip to the fastener is the same as the distance from the midpoint of the grip to the center of the square drive, and you handle it properly, the torque will be theoretically the same.

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    Danny, if you put a socket on the click type torque wrench and pull with your hand at the handle, then when you reach the set torque it will click. If you put your hand at the half way point of the wrench and pull, it will click when you reach the set torque but, you will pull much harder to do it.

    What I am saying is, it don't matter how short or long you make the handle, it will always click at the preset torque.

    Now, with an extension on the wrench where a socket would be it does not change the way the wrench reads torque at the ratchet head. What changes is the actual torque applied to the bolt or nut because of the length of the extension. You can still pull on the torque wrench anywhere on it's length you want to or put a cheater bar on it and it won't affect the torque it's set to.

    So, you need a formula to figure the torque setting you have to set the wrench to to get the correct torque at the end of the extension.

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    Danny, Quote; "If the extension was set at 90* to the handle thereby not adding lenght would the setting on the wrench be the same as the torque on the bolt?" No.

    There would still be some extension over the "formula" of the wrench because you've created a right triangle with the hypotenuse now the lever arm rather than the intended 'side A', a created side B, the extension at 90° and you know what Pathagorus said about hypotenuses.

    These extensions used to be available for torque wrenches, along with a little compensation chart. Probably still are.

    Any extension can be compensated for with a simple calculation. With a 6" extension, parallel to a torque wrench with 12" between the handle pin and the center of the drive square, the torque value set on your clicker wrench should be reduced by 1/3, the same ratio of the extension over the standard wrench. 120 ft. pounds becoming 80 ft. pounds.

    You've just created a torque wrench where foot pounds have become "foot and a half" pounds. By the way, extensions on the handle of course have no bearing on when the "click" will occur, it will be the same with longer arc/less pressure but the wrench won't know it, except for the quite probable disabling of the function of the handle pin, where the handle sleeve should never come into contact with the body of the wrench, changes the "12" length.

    Bob


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