Random question about leverage for mechanics and mathematicians

Discussion in 'Anything Goes' started by Kevin509, Oct 15, 2013.

  1. Kevin509

    Kevin509 New Member

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    Considered putting this in the garage section but it doesn't specifically have to do with our VFRs so I put it here.

    I work at a car dealership doing a little bit of everything really and today I was putting the snow tires/wheels on my boss' pickup. The wheels are a relatively deep dish style so I was using an extension on the torque wrench to keep from busting my knuckles on the fender of the truck. Well my boss came out and gave me a big lecture about how adding an extension on the torque wrench changes the amount of torque you're applying to the nuts and told me never to do it that way again.

    Now, I'm no expert at these things, but as far as I understand it the amount of leverage, and therefore torque being applied is dependent on the distance from the nut to the end of the tool. I fail to see how the length of the socket with or without an extension on it has an effect on leverage because it doesn't change the length of the tool in a horizontal sense for lack of a better way to explain it.

    Is there something I'm missing?

    Sent from my LG-LS970 using Tapatalk
     
  2. skimad4x4

    skimad4x4 "Official" VFRWorld Greeter

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    I can sort of see both sides:mad:

    In theory the force applied by a lever is indeed linked to the length of the lever and the forces applied to the end of the lever. So just stepping the actually point of rotation a short distance away from the item being torqued really is not going to materially distort the outcome. The problem comes with the point of rotation moving out of alignment, as you start getting additional twisting forces coming into play. The effect would be for a torque wrench to potentially trip early - leaving the nut under-torqued. By how much? - I have no idea, but its probably quite small provided it remains close to in line. I don't think I have ever seen any assessment done on how bad that could distort results.

    Obviously the risk of things getting miss-aligned increases with length, so using a whacking great extension bar - especially when it's not actually needed is not good practice.

    When It comes to fitting my own snowtyres there is no way I could tighten the bolts directly with a torque wrench - so I use a short extension bar which is long enough to get the torque wrench clear of the sides of the tyres. After dialling in the correct torque I just take care to make sure the torque wrench remains directly in line with the wheel nut.

    I suspect it would be more of an issue on highly stressed components. I wonder how your boss suggests you should torque down things like an engine head/block or even rocker cover bolts where you often need to work over/around other components and the only possible way to torque them may be by using a extension bar???

    OK If you were fixing panels on The Hubble Space Telescope absolute perfection is the way to go and they can afford specialist tools and jigs specifically calibrated to deliver the required torque. But in a garage fitting car tyres it seems a bit OTT...but then again he pays the bills..



    SkiMad
     
  3. Badbilly

    Badbilly Official VFRWorld Troll Of The Year!

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    Have the cheap SOB buy you a digital.
     
  4. danny_tb

    danny_tb New Member

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    I agree with Skimad. If you don't want to keep your job, feel free to tell him that an experienced professional automotive engineer (me) says he's a fcuking w@nker for thinking that it will make any meaningful difference! ;)
     
  5. jethro911

    jethro911 Member

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    You boss is full of it. I believe that he heard something second hand and now applies it wherever he sees fit to seem knowlegable.


    Check this out. The only time you need to calculate the torque because of an added adapter is when you change the fulcrum. It happens from time to time in situations where you use a torque adapter such as in this scenario. I've had to use this type of calculator a thousand times when installing propellors on aircraft because a torque adapter is often used due to the fact that a torque wrench won't fit in the tight space.

    http://cncexpo.com/TorqueAdapter.aspx

    In your case you simply used an extension which didn't change the fulcrum meaning that the working length of the tool didn't change and therefore the reading is accurate.
     
  6. Badbilly

    Badbilly Official VFRWorld Troll Of The Year!

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  7. vfr2k2

    vfr2k2 New Member

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    Your BOSS is absolutely correct. By virtue of being the boss! He is ultimately responsible for your performance. Defer to his wisdom and ask him to explain to you what would be the proper way to torque those lugs and possibly where you might reference his suggestion. Be eager to want to do things right. When he justifies his methods..... thank him earnestly......if he can't....tell him to eat CROW!!!! He may not enjoy his new diet....
     
  8. Kevin509

    Kevin509 New Member

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    Thanks for the replies guys. It looks like I was right in thinking it makes no or negligible difference, but as some of you have said, I'll do it 'his way' because he's the boss.

    He did, actually. A big hideous purple bagger thing. (black cherry, he called it. Don't let him catch you calling it purple lol) But he sold that when he got his XLR-V.
     
  9. vfourbear

    vfourbear New Member

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    Just use a hammer.
     
  10. Badbilly

    Badbilly Official VFRWorld Troll Of The Year!

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    That alone might justify why he wanted his nuts torqued.
     
  11. vfr2k2

    vfr2k2 New Member

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  12. Badbilly

    Badbilly Official VFRWorld Troll Of The Year!

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  13. Vfryellow

    Vfryellow New Member

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    Using a extension on a torque wrench does change your final torque speck. Here is why. All extensions twist a set amount depending on its over all length. If you go on snapons web sight all there extensions give you a value of deflection. So if i have a extension that is 12 inches long and has a twist deflection of 1.1 and you want to torque a nut to 100 ft pounds. You need to set wrench to 101. Now with all that said does one or two pounds make a big deal? NO........ Just my two cents.
     
  14. danny_tb

    danny_tb New Member

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    It actually increases the friction between the nut and stud by adding torque in a direction that is trying to bend the stud (caused by the increased lever arm in this direction, due to the presence of the extension - the added torque is at rightangles to the applied torque). This increased friction resists the applied torque, resulting in the nut failing to rotate as far as it would have without the extension, resulting in less elastic strain in the stud, and consequently lower clamping load. Sorry, but twist of the extension doesn't cause a torque reduction (and this would be easily proven with a free body diagram).

    If using an extension was really so bad, perhaps the OP's boss might like to contact the manufacturer of one of my torque wrenches to tell them why they shouldn't have added the extension to the kit: ;)

    ImageUploadedByTapatalk1382095598.037803.jpg
     
  15. Badbilly

    Badbilly Official VFRWorld Troll Of The Year!

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    This topic may be slipping toward the long walk on a short pier debate. After all "el chingon " did have a Harley..
     
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