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Torque-wrench adapter offsets

  • 21-10-2013 2:17pm
    #1
    Registered Users, Registered Users 2 Posts: 20,195 ✭✭✭✭


    Greetings.

    For those of you who, like me, occasionally find themselves confronted with a fastener on a fuel line or a HVAC refrigerant hose armed with nowt but a torque spec and a regular torque-wrench. A socket can't be got on the thing, and you have a crowfoot adapter but, yikes, the Leaving Cert. physics nerd in you knows that this will screw up the torque setting. Well fear not, for this is how to correct it.

    The first thing to know is that if the wrench is fitted to the adapter at a 90-degree angle, there is no adjustment required. Zip. Nada. Bubkes. All well-and-fine until you need, for space/access reasons, to keep the whole tool straight, or maybe even at 45 degrees.

    So, the equation goes like this:
    TS == (TR x DW)/(DW+(DA*cos(Z)))
    

    ...where:

    TS == torque setting at the wrench
    TR == torque required, i.e. torque spec of the fastener
    DW == Distance from the wrench pivot-point to the centre of the handle
    DA == Distance from the centre of the adapter "jaw" to the wrench pivot-point
    Z == Angle made by the wrench and the adapter

    Say we have a fastener rated at 50 lb. ft. The distance from the centre of the square-drive on our wrench to the centre of the handle is 18 inches. The distance from the centre of the adapter "jaw" to the centre of the wrench square-drive is 6 inches. We want to keep the whole lot straight, i.e. the angle of the adapter to the wrench will be zero degress. So:

    cos(0) == 1

    Torque setting to use == 50 x 18/(18+(6 x 1)) == 37.5 lb. ft.

    Now say we have the same set-up, but this time we want the adapter at a 90-degree angle to the wrench. So:

    cos(90) == 0

    Torque setting to use == 50 x 18/(18+(6 x 0)) == 50 lb. ft.

    ...i.e. no adjustment from specified torque is necessary.


    As a speadsheet formula (as tested in OpenOffice Calc):
    =((TR*DW)/(DW+(DA*(COS(RADIANS(Z))))))
    

    As a Unix "bc" calculation:
    TS=$(echo "scale=10; $TR*$DW/($DW+($DA*c($Z*(4*a(1))/180)))" | bc -l)
    


    Happy nerding!! :D


Comments

  • Registered Users, Registered Users 2 Posts: 12,822 ✭✭✭✭galwaytt


    jimgoose wrote: »
    Greetings.

    For those of you who, like me, occasionally find themselves confronted with a fastener on a fuel line or a HVAC refrigerant hose armed with nowt but a torque spec and a regular torque-wrench. A socket can't be got on the thing, and you have a crowfoot adapter but, yikes, the Leaving Cert. physics nerd in you knows that this will screw up the torque setting. Well fear not, for this is how to correct it.

    The first thing to know is that if the wrench is fitted to the adapter at a 90-degree angle, there is no adjustment required. Zip. Nada. Bubkes. All well-and-fine until you need, for space/access reasons, to keep the whole tool straight, or maybe even at 45 degrees.

    So, the equation goes like this:
    TS == (TR x DW)/(DW+(DA*cos(Z)))
    

    ...where:

    TS == torque setting at the wrench
    TR == torque required, i.e. torque spec of the fastener
    DW == Distance from the wrench pivot-point to the centre of the handle
    DA == Distance from the centre of the adapter "jaw" to the wrench pivot-point
    Z == Angle made by the wrench and the adapter

    Say we have a fastener rated at 50 lb. ft. The distance from the centre of the square-drive on our wrench to the centre of the handle is 18 inches. The distance from the centre of the adapter "jaw" to the centre of the wrench square-drive is 6 inches. We want to keep the whole lot straight, i.e. the angle of the adapter to the wrench will be zero degress. So:

    cos(0) == 1

    Torque setting to use == 50 x 18/(18+(6 x 1)) == 37.5 lb. ft.

    Now say we have the same set-up, but this time we want the adapter at a 90-degree angle to the wrench. So:

    cos(90) == 0

    Torque setting to use == 50 x 18/(18+(6 x 0)) == 50 lb. ft.

    ...i.e. no adjustment from specified torque is necessary.


    As a speadsheet formula (as tested in OpenOffice Calc):
    =((TR*DW)/(DW+(DA*(COS(RADIANS(Z))))))
    

    As a Unix "bc" calculation:
    TS=$(echo "scale=10; $TR*$DW/($DW+($DA*c($Z*(4*a(1))/180)))" | bc -l)
    


    Happy nerding!! :D

    Indeed: torque, a subject I spent many years at.

    One of the best wrenches out there is Torqueleader, from MHH Engineering in the UK.

    This is one of their pages, which is good to get a look at: http://www.torqueleader.com/torqueleader-support/torque/ have a look at the downloads section at the top of that page.

    They have a YouTube channel as well, here: http://www.youtube.com/torqueleader

    They sell non-length dependant wrenches too, if you're so inclined.

    For refrigeration and other fluid fitting tasks, their ATB range is handy.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • Registered Users, Registered Users 2 Posts: 20,195 ✭✭✭✭jimgoose


    galwaytt wrote: »
    Indeed: torque, a subject I spent many years at.

    One of the best wrenches out there is Torqueleader, from MHH Engineering in the UK.

    This is one of their pages, which is good to get a look at: http://www.torqueleader.com/torqueleader-support/torque/ have a look at the downloads section at the top of that page.

    They have a YouTube channel as well, here: http://www.youtube.com/torqueleader

    They sell non-length dependant wrenches too, if you're so inclined.

    For refrigeration and other fluid fitting tasks, their ATB range is handy.

    Oh yes, actual torque spanners be the job for fluids, but for the amount the Enthusiastic Amateur Fartbollix such as myself has to deal with it, the trigonometry method is just fine, and rather cheaper! :D


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