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  1. #1
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    Newton and his meters of force (8nM tightening)

    So I got a new pair of carbon bars today, Truvativ Noirs, and after I finished intallin' them on my rig, I took a look at the "manual" (you know the 10 language tiny font piece of onion paper &$#*@!.) Whew, anyway, they say to tighten to no more than 8nM. Now I don't know what 8nM feels like, but it there an equivalent "human" scale? You know, hand tight, one quarter crank past hand tight, put your weight into it and crank that puppy down, etc. Anyone know this mysterious Newton and his meters?

    Many thanks,

    Noir.
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  2. #2
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    I would not stick my neck out installing carbon parts without a torque wrench. Too low torque the bars slip, too much they crack.
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  3. #3
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    I use Ritchey WCS bars and stem, i never needed a torque wrench. Always used a short allen key to give me just enough leverage to tighten beyond the slipping point but no more. Developed a pretty good feel in the process, and when checked with a torque wrench i always crank it down 10-15% under spec.

  4. #4
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    are these bars on a 29er or 26er?
    -It's time to shred some mild to moderate gnar!!

  5. #5
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    both, neither, doesn't make a difference texass. <

    How about my stem choice? I've heard mutterings about stems being "incompatible" with carbon. Any way to tell/check? I suspect it doesn't Really matter too much because otherwise all the stems would be labeled one way or the other.
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  6. #6
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    But, being in the 29er forum, you'd be safe to assume a 29er..
    Jamis Dakota '06
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  7. #7
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    Quote Originally Posted by NameTaken View Post
    So I got a new pair of carbon bars today, Truvativ Noirs, and after I finished intallin' them on my rig, I took a look at the "manual" (you know the 10 language tiny font piece of onion paper &$#*@!.) Whew, anyway, they say to tighten to no more than 8nM. Now I don't know what 8nM feels like, but it there an equivalent "human" scale? You know, hand tight, one quarter crank past hand tight, put your weight into it and crank that puppy down, etc. Anyone know this mysterious Newton and his meters?

    Many thanks,

    Noir.

    Buy a torque wrench .... then you'll know exactly what 8 N-m feels like

  8. #8
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    Quote Originally Posted by elgordo View Post
    Buy a torque wrench .... then you'll know exactly what 8 N-m feels like
    Not really. Torque wrenches dont have the same feel as a small allen wrench.

  9. #9
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    In human terms, it feels like a little less than 6 ft#. If you don't know how to measure this, I'd either stick with metal bars or get someone that knows what they are doing install it. Or both.

  10. #10
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    Quote Originally Posted by syl3 View Post
    I use Ritchey WCS bars and stem, i never needed a torque wrench. Always used a short allen key to give me just enough leverage to tighten beyond the slipping point but no more. Developed a pretty good feel in the process, and when checked with a torque wrench i always crank it down 10-15% under spec.
    This is not the best advice I've ever heard. You can't know if you are just past the slipping point unless you tighten->ride->it slips->tighten->ride->it slips->tighten->ride->doesn't slip. You get my point? Also, if you are 10-15% below spec, then you are well under the factor of safety built into that spec. Beyond that...if you install the fastener by hand and then check with a torque wrench, you're readings will be skewed high because of the difference between static and kinetic friction.

    I'm sorry, but I've known a lot of good mechanics in different fields and nobody has a calibrated hand. If it is a torque critical application they will use a torque wrench.

    I'm sure some bar stem combos are less sensitive to torques, but why risk your purchase...spend a few bucks on a decent torque wrench, and buy yourself some peace of mind.

  11. #11
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    Quote Originally Posted by NameTaken View Post
    How about my stem choice? I've heard mutterings about stems being "incompatible" with carbon..
    incompatible how? uneven pressure on the bar? if you mean slipping, use friction paste when installing a carbon bar.

  12. #12
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    Torque wrenches aren't that expensive versus buying another set of bars. So many parts come with torque specs on them these days that the torque wrench is pretty much THE most vital tool in the box.

    Friction paste is also a must.

  13. #13
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    It would not surprise me to learn that every rider who owns a torque wrench had a bad experience over-torquing a part, which caused them to spend money on the replacement part that would be in the ball park of the cost of a torque wrench. Learn from others, and get a torque wrench. If not now, sooner or later with the ever-increasing number of carbon parts around, you will crack or break a part, and hopefully that failure doesn't occur in the midst of a ride - the laws of physics do not cease to exist just because you tried your best to guess on the torque. Plus, there is the satisfaction of knowing that the parts have been properly torqued when you are hammering and really put stress on the bike.

  14. #14
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    excellent advice... +1

    Torque wrench is way less expensive than the replacement bar...

    Quote Originally Posted by keeb View Post
    This is not the best advice I've ever heard. You can't know if you are just past the slipping point unless you tighten->ride->it slips->tighten->ride->it slips->tighten->ride->doesn't slip. You get my point? Also, if you are 10-15% below spec, then you are well under the factor of safety built into that spec. Beyond that...if you install the fastener by hand and then check with a torque wrench, you're readings will be skewed high because of the difference between static and kinetic friction.

    I'm sorry, but I've known a lot of good mechanics in different fields and nobody has a calibrated hand. If it is a torque critical application they will use a torque wrench.

    I'm sure some bar stem combos are less sensitive to torques, but why risk your purchase...spend a few bucks on a decent torque wrench, and buy yourself some peace of mind.

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    as a professional bicycle mechanic (working as a workshop manager in a busy workshop with a high number of mechanics working for me) one of my regular tasks is to assess the work my mechanics are producing, which involves lots of investigation of both PDIs on new bikes and QC of repair work

    the first tool I reach for is the RS torque measurement wrench, and with some of the less experienced mechanics, the results can be quite shocking, as they often ignore the torque wrench in favour of their Park P-Handle allen wrenches (despite my constant advice)

    its SO easy to get torque wrong when working by hand, and I see this a lot with customers who have done their own wrenching at home and damaged components because they have not used a torque wrench

    my advice? buy a quality (does not mean expensive) torque wrench and use it every time you work on your bike

    not just talking about working on CF finishing kit, but every bolt on your bicycle will benefit from use of a torque wrench - including cassette lock rings, disc brake mounting bolts, headset cap bolts, crank bolts, etc.

    the torque you "think" you are using when you do it by hand, is often very different to where it needs to be when actually checked with a torque wrench

    be aware that torque wrenches do need re-calibration, although for a home mechanic this is less of an issue, as in my workshop I am using this tools dozens of times every single day

    also, be very aware that simple mistakes like getting grease under the head of a bolt on your stem faceplate will allow you to over tighten the bar clamp whether using a torque wrench or allen key to tighten (the grease reduces the rotational friction between the bolt head and stem clamp surface, giving a false torque reading)

    its a little scary how little information is put out about this, only Thomson and Easton seem to include this info with their products?

  16. #16
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    with proper torque, there are no incompatible stems...

  17. #17
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    Quote Originally Posted by keeb View Post
    This is not the best advice I've ever heard. You can't know if you are just past the slipping point unless you tighten->ride->it slips->tighten->ride->it slips->tighten->ride->doesn't slip. You get my point? Also, if you are 10-15% below spec, then you are well under the factor of safety built into that spec. Beyond that...if you install the fastener by hand and then check with a torque wrench, you're readings will be skewed high because of the difference between static and kinetic friction.

    I'm sorry, but I've known a lot of good mechanics in different fields and nobody has a calibrated hand. If it is a torque critical application they will use a torque wrench.

    I'm sure some bar stem combos are less sensitive to torques, but why risk your purchase...spend a few bucks on a decent torque wrench, and buy yourself some peace of mind.
    I have a torque wrench i just don't use it on bars and stems anymore. You can get a calibrated hand if you always use the same length allen.

    i have had a single instance of slip caused by not paying attention while switching bars and eating gels 5 minutes before a race, but i have not cracked any bars so far.

    disclaimer: i assemble ~20 bikes per week, if you want to learn this at home do yourself a favor and at least replace titanium stem bolts, you will **** them up.

  18. #18
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    Quote Originally Posted by osokolo View Post
    with proper torque, there are no incompatible stems...
    that's not true, contact area is very important. stem design makes a huge difference, specifically one piece vs 2 piece fastenings

  19. #19
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    Quote Originally Posted by hampstead bandit View Post




    also, be very aware that simple mistakes like getting grease under the head of a bolt on your stem faceplate will allow you to over tighten the bar clamp whether using a torque wrench or allen key to tighten (the grease reduces the rotational friction between the bolt head and stem clamp surface, giving a false torque reading)

    its a little scary how little information is put out about this, only Thomson and Easton seem to include this info with their products?
    Greasing the heads of the bolts will have no negative effect on the proper torque. If anything the opposite is true; you'll get a false reading due to added friction.


    http://www.bikethomson.com/blog/wp-c...X2-BMXFull.pdf

    Torque wrench - Wikipedia, the free encyclopedia

  20. #20
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    8nm is a fair bit of torque for a carbon bar. I would be surprised if you over torqued it. However it's always ideal to have the right tool for the job. With bicycles getting lighter and lighter and consumers expecting the same durability I think that proper installation is mandatory. Working on bicycles isn't hard but when working with higher end parts it does take a certain amount of care to do things correctly.

  21. #21
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    OP, 8nM is not much. If you are just starting to wrench on more expensive parts I highly recommend buying a torque wrench. They aren't expensive and can save their cost with just one broken part.

    For others, if you are working on your bike feel free to wing it. If you are working on my bike you better be using a torque wrench...
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  22. #22
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    Quote Originally Posted by customfab View Post
    8nm is a fair bit of torque for a carbon bar.
    Never even noticed that part of the post.

    Most of the stems I've owned/own had/have a 5nm recommended torque.

    I love my torque wrench, and it sees way more use than I would've ever imagined.

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  23. #23
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    can you list a few carbon bar INCOMPATIBLE stems please?

    I have stems with both one piece and 2 piece fastenings. The only difference is weight...

    However - I would appreciate some factual explanation with examples... Thanks...

    Quote Originally Posted by syl3 View Post
    that's not true, contact area is very important. stem design makes a huge difference, specifically one piece vs 2 piece fastenings

  24. #24
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    you could also use a nail clipper.

    Doing the Crank the Shield this year?

  25. #25
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    Quote Originally Posted by NameTaken View Post
    ....they say to tighten to no more than 8nM.
    Just a warning, the 8 Newton meter is a limit for the bar itself. Above that torque you could crush the handlebar. What is important, is that the maximum torque for most light weight stems is less. For example a Thomson Elite X4 stem specifies a clamp bolt torque of 4.0 Nm. And people are surprised that they have cracked face plates.

    If you are going to work on your bike get a torque wrench.
    The trouble with having an open mind is that people will insist on trying to put things in it.

  26. #26
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    Quote Originally Posted by CB2 View Post
    Greasing the heads of the bolts will have no negative effect on the proper torque. If anything the opposite is true; you'll get a false reading due to added friction.
    according to engineering sources and the information contained in current Easton and Thomson products we regularly receive into the workshop, grease under the heads of the bolts will actually give a false reading as less friction is experienced when tightening the bolt head against the stem face plate bore holes, or the stem steerer clamp bore holes

    grease reduces friction during assembly, it does not increase friction...unless I have missed something critical in my professional (cytech) training?

  27. #27
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    Quote Originally Posted by CB2 View Post
    Greasing the heads of the bolts will have no negative effect on the proper torque. If anything the opposite is true; you'll get a false reading due to added friction.


    http://www.bikethomson.com/blog/wp-c...X2-BMXFull.pdf

    Torque wrench - Wikipedia, the free encyclopedia
    Quote Originally Posted by hampstead bandit View Post
    according to engineering sources and the information contained in current Easton and Thomson products we regularly receive into the workshop, grease under the heads of the bolts will actually give a false reading as less friction is experienced when tightening the bolt head against the stem face plate bore holes, or the stem steerer clamp bore holes

    grease reduces friction during assembly, it does not increase friction...unless I have missed something critical in my professional (cytech) training?
    Some torque specs are with lubrication, some are not.

    Using lube when the spec doesn't call for it will likely over load the bolt/part (even though torque is in spec).

    Leaving it dry when lube is called for will likely leave the clamping force on the low side (even though torque is in spec).

    In more sophisticated applications they specify "bolt preload", which is independent of bolt torque under varying frictional forces. Or they very narrowly specify all the conditions of the assembly (torque, fastener material and surface finish/plating, grade of thread, mating part finish, the application of torque modifiers or thread lockers, etc.).

    You can take this all the way back to the "should I grease my square taper spindle" discussion.

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  28. #28
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    Quote Originally Posted by Ronnie View Post
    Just a warning, the 8 Newton meter is a limit for the bar itself. Above that torque you could crush the handlebar. What is important, is that the maximum torque for most light weight stems is less. For example a Thomson Elite X4 stem specifies a clamp bolt torque of 4.0 Nm. And people are surprised that they have cracked face plates.

    If you are going to work on your bike get a torque wrench.

    +1 for sure!

  29. #29
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    Quote Originally Posted by hampstead bandit View Post
    according to engineering sources and the information contained in current Easton and Thomson products we regularly receive into the workshop, grease under the heads of the bolts will actually give a false reading as less friction is experienced when tightening the bolt head against the stem face plate bore holes, or the stem steerer clamp bore holes

    grease reduces friction during assembly, it does not increase friction...unless I have missed something critical in my professional (cytech) training?
    I was referring to the added friction of no grease.

    I also looked through the attached Thomson instructions and couldn't find anything about not greasing the heads, which I don't normally do (I prep the threads appropriately), but I can't see it having a negative effect.

    I may be wrong on this but I thought torque was a measure of the tension on the threads.

  30. #30
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    CB2,

    Fleas' post is spot on. Reference "Mechanical Engineering Design" By: Joesph Shigley. Lubrication decreases collar friction which allows a greater amount of applied torque to result in clamping force.

  31. #31
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    Quote Originally Posted by texasnavy05 View Post
    are these bars on a 29er or 26er?
    I needed that chuckle.

  32. #32
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    Quote Originally Posted by CB2 View Post
    I was referring to the added friction of no grease.
    Unless otherwise specified (as in the Thompson instructions), bolt torque specs are typically dry.
    Quote Originally Posted by CB2 View Post
    I also looked through the attached Thomson instructions and couldn't find anything about not greasing the heads, which I don't normally do (I prep the threads appropriately), but I can't see it having a negative effect.
    Greasing the heads reduces the friction, meaning you get to a higher clamping force for the same torque, which could be overload (negative effect).
    Quote Originally Posted by CB2 View Post
    I may be wrong on this but I thought torque was a measure of the tension on the threads.
    Torque is a measure of the friction between the bolt and the receptacle. What you are trying to get to is clamping force. The torque/clamping force relationship is driven by the friction in the system, which is affected by any lubricant on any surface.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  33. #33
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    Carbon with torque wrench = bad jue jue
    You ask why I ask why the hell not.!.
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  34. #34
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    Quote Originally Posted by teamdicky View Post
    Never even noticed that part of the post.

    Most of the stems I've owned/own had/have a 5nm recommended torque.

    I love my torque wrench, and it sees way more use than I would've ever imagined.

    Wow! torque wrenches tend to be pricey but that one just looks like it would cost your first born.


    Isn't most things carbon around 5nm?

    Hell I think they even sell something specifically for carbon bar torquing...


    here it is:
    Cutter Torque Wrench - 5Nm from Realcyclist.com
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  35. #35
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    Quote Originally Posted by KVW View Post
    Wow! torque wrenches tend to be pricey but that one just looks like it would cost your first born.


    Isn't most things carbon around 5nm?

    Hell I think they even sell something specifically for carbon bar torquing...
    I bought a cheap 4nm Ritchey Torqkey for travel purposes since I have to remove my faceplate to get the bike in the box. It's nice, but I'll probably travel with the Topeak now that I own it. Sure, it was expensive, but I thought the $40 torque wrench was expensive... until it failed forcing me to buy something better. I use it a lot more than I woulda imagined, and I never worry about stripping a component or popping the head off a rotor bolt anymore.

    Just checked around my room.
    stem faceplates 4nm
    seat post clamp 5nm
    stem bolts (I've got a carbon steer tube) 11nm
    MOOTSpost rail clamps 8nm
    Hayes levers 3.37nm
    Eriksen post 12-15nm
    Bolt-on skewers 9.5nm
    Niner EBB 21nm
    Paragon slider bolts (ti bolts) 26.4-28.6nm
    Rotor bolts 6.2nm
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  36. #36
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    That Topeak looks sweet on QBP. I would cry if it got dropped though.

    I have been using the park beam styles. They arent the best but they get in the correct ballpark range of everything. I also not on any stupid light parts though
    Raised in a Chicken-Coop by Chickens

  37. #37
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    Quote Originally Posted by Sheepo5669 View Post
    That Topeak looks sweet on QBP. I would cry if it got dropped though.

    I have been using the park beam styles. They arent the best but they get in the correct ballpark range of everything. I also not on any stupid light parts though
    I don't run anything stupid light, but Iove hat reassuring "beep."
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  38. #38
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    Beam styles are the least accurate. Click are next. The most accurate are dial type torque wrenches. Not that it particually matters for this application. Personally I use ratcheting "click" type torque wrenches.

  39. #39
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    That's damn sexy!
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    Your fear of looking stupid is holding you back.

  40. #40
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    BTW, Park Tool TW-5 wrench seems nice enough and is available for $83.30. On amazon with free shipping.

  41. #41
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    Quote Originally Posted by MattC555 View Post
    Beam styles are the least accurate. Click are next. The most accurate are dial type torque wrenches. Not that it particually matters for this application. Personally I use ratcheting "click" type torque wrenches.
    What is a "dial type" wrench?
    All I know of are: beam, click & electronic (strain gauge).
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  42. #42
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    Quote Originally Posted by meltingfeather View Post
    What is a "dial type" wrench?
    All I know of are: beam, click & electronic (strain gauge).



  43. #43
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    Quote Originally Posted by MattC555 View Post
    that's a beam-type wrench.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  44. #44
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    This is the beam type I was talking about. Technically the dial torque wrench uses a beam too, but the beam is internal and the dial typically has a max. load reading. They are far more accurate than a traditional beam torque wrench, hence why I made the distinction. These wrenches are sometimes fitted with electronics, to aid in production.

  45. #45
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    Quote Originally Posted by MattC555 View Post
    Technically the dial torque wrench uses a beam too, but the beam is internal and the dial typically has a max. load reading. They are far more accurate than a traditional beam torque wrench, hence why I made the distinction. These wrenches are sometimes fitted with electronics, to aid in production.
    10-4, I just thought you were talking about some fundamentally different type of measurement. FWIW I don't think beams with dials are "far more accurate" than simple beams, they just eliminate a couple of potential sources of error, which can also be eliminated by proper use.
    Anyway...
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  46. #46
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    Quote Originally Posted by NameTaken View Post
    ......Anyone know this mysterious Newton and his meters?

    Many thanks,

    Noir.
    No mistery at all:
    1 Newton= 0.8 Kg=1.7 Lbs
    1 meter= 40 Inch

    Hold a 1.7(x8) pounds weight with a 1meter (40 inch) long bar as close to the edge as you can. (If dividing length multiply weight accordingly)
    You pretty much get the idea of "how it feels"

    I never used a torque wrench in my life
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  47. #47
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    In general practice the gear driven dials are going to have finer measurement graduations.

    Really my original accuracy statement is both through practice, my job involves designing and torque testing a lot of fastened joints, and a snapon cataloge I read awhile back. None of the torque wrenches I have at work have their accuracy displayed. So after researching all of the torque sensing devices in my lab, my rule of thumb is: torque transducer > dial > click > beam.

  48. #48
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    Quote Originally Posted by MattC555 View Post
    In general practice the gear driven dials are going to have finer measurement graduations.
    that is precision, not accuracy, right?
    Quote Originally Posted by MattC555 View Post
    Really my original accuracy statement is both through practice, my job involves designing and torque testing a lot of fastened joints, and a snapon cataloge I read awhile back. None of the torque wrenches I have at work have their accuracy displayed. So after researching all of the torque sensing devices in my lab, my rule of thumb is: torque transducer > dial > click > beam.
    GTK, thanks.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  49. #49
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    Quote Originally Posted by meltingfeather View Post
    that is precision, not accuracy, right?
    Accuracy, how it's been defined to me anyway, is the difference between the intended value and the desired value.

    Precision, as defined to me, is the repeatability of a component or function. Used to express the total variability of a single component or function over multiple events. Consistency, w/o regard to accuracy.

    Finer graduations, or measurement resolution, will allow the user to torque something to a greater accuracy, having less known difference between the intended and specificed value.

    It's all semantics really

  50. #50
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    Quote Originally Posted by MattC555 View Post
    Accuracy, how it's been defined to me anyway, is the difference between the intended value and the actual value.
    FIFY.
    Intended and desired are the same in my mind.
    Quote Originally Posted by MattC555 View Post
    Precision, as defined to me, is the repeatability of a component or function. Used to express the total variability of a single component or function over multiple events. Consistency, w/o regard to accuracy.
    Exactly. Finer gradations mean you can hit the same point on the scale pretty well, but that doesn't mean the point you're hitting is the actual value... that's accuracy, as you pointed out.
    Quote Originally Posted by MattC555 View Post
    Finer graduations, or measurement resolution, will allow the user to torque something to a greater accuracy, having less known difference between the intended and specificed value.
    A finer measurement scale does not magically calibrate the instrument or reduce measurement errors in it. If so, you could just draw a finer set of lines in your simple beam wrench and get to the same spot.
    Quote Originally Posted by MattC555 View Post
    It's all semantics really
    Probably
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  51. #51
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    meltingfeather,

    I'll buy what you're selling

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    I only use a TW, but then again I had to spend some coin to buy one for work, and then send it off and spend some more to recertify it every year so you best believe I will use it every chance I get. No one will ever be able to tell me that my fasteners are not to spec. I also would never by a cheap TW, either. My boss learned the hard way to the tune of several thousands of dollars.

  53. #53
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    Quote Originally Posted by meltingfeather View Post
    ...
    A finer measurement scale does not magically calibrate the instrument or reduce measurement errors in it. If so, you could just draw a finer set of lines in your simple beam wrench and get to the same spot.
    ...
    Right.

    One of our plants works with fasteners a lot. They have a torque wrench for every range from oz.-in. to some HUGE TW with a 6 ft. handle that is only used with a big vise that is bolted to a steel frame that is lagged to a concrete floor. It is for checking 3" crimp nuts with thread locker.

    Quote Originally Posted by From Proto Tools
    MICROMETER TORQUE WRENCHES
    Proto offers 1/4" - 1" drive in both ratchet and fixed head styles, covering torque ranges from 10 in. lb. to 2,000 ft. lb., 14 cmkg through 90 mkg, and 10-800 Newton meters. Proto micrometer torque wrenches are calibrated to ±3% of torque reading clockwise and ±6% of torque reading counterclockwise at 20% to 100% of full scale. Each Proto torque wrench includes a Calibration Certificate that verifies the actual readings and includes a unique torque wrench serial number. Proto torque wrenches are certified to meet, or exceed, the standards specified in ANSI B107.14-1994. Specialty ordered certified micrometer wrenches to ±2% one direction are available upon request. Pre-set torque wrenches are also available on special request.

    DIAL TORQUE WRENCHES
    Proto wrenches are accurate to ±3% actual torque reading in both directions over a range 20% to 100% of full scale. Certified Proto dial torque wrenches may be special ordered and are traceable to the National Institute of Standards and Technology and exceed Government Specification GGG-W00686c.
    Notice the accuracy is not much different, but the dial type TW, with higher readout/indicator resolution (it's just easier to read), usually produces better results when used by several different people (gauge repeatability and reproducibility or GR&R). The result is still dependent on the user of the tool, but the tool is easier to use by virtue of its indicator - the measurement error can be (but is not magically ) reduced this way.

    Funny story (quickly):
    After I complained that I couldn't remove my wheels from my truck, I had the installer tell me that they "always use a torque wrench". Of course, they had already over-tightened them with the impact driver to about 150 ft-lbs. When they used the TW set at 100 ft-lbs, they thought that it was telling them that all the lugs were at 100 ft-lbs. To convince him that he was doing it wrong I had him set the torque wrench at 120 ft-lbs and attempt to remove the lug nuts. I think they needed a new torque wrench after that.

    -F
    It's never easier - you just go faster.

  54. #54
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    Quote Originally Posted by osokolo View Post
    I have stems with both one piece and 2 piece fastenings. The only difference is weight...

    However - I would appreciate some factual explanation with examples... Thanks...
    I remeber last year there was a big debate about the road carbon bars and carbon steerer tubes failing, the ones that came stock on high end Trek bikes, and Trek blamed it on people changing the one-piece Bontrager stems with other 2-piece designs just to save a few grams.

    eta: here's a link i found with a quick search: Steered wrong? Racers concerned about broken carbon steerer tubes

    according to trek the risk is clearly linked to the contact area:

    3) Use only the stem brand and model that came with the bike, because not all stems will work with carbon steerers. Often the lighter the stem, the less chance it will be compatible with a carbon steerer. Weight-relieving cutouts on the stem clamp and steerer interface can create stress risers.
    Last edited by syl3; 03-03-2012 at 06:17 AM.

  55. #55
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    Quote Originally Posted by meltingfeather View Post
    Torque is a measure of the friction between the bolt and the receptacle. What you are trying to get to is clamping force. The torque/clamping force relationship is driven by the friction in the system, which is affected by any lubricant on any surface.
    Torque should not be thought of as a measure of friction (friction is a result, not a cause, of proper torquing).

    Torque is a measure of ROTATING force. Twisting force plus the simple machine we call a screw (or bolt) creates clamping force (rotating force becomes linear force).
    You better just go ahead and drop that seatpost down to the reflector... the trail gets pretty rough down there.

  56. #56
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    The question is WHY are you tightening a fastener to a specific torque?

    As Fleas point out, it is to give the fastener a 'pre load'. Think of the fastener as a really stiff spring. By torqueing it to a certain value, you are creating xxx amount of spring force.

    You need to know the conditions under which the spec was made. i.e.: were the threads dry, under bolt head greased, etc. All of which will affect the value of the pre load. For the same torque -> More friction = less pre load, less friction = more pre load.

    From a fastner perspective:
    The proper way to torque any fastener is to lubricate all surfaces. This minimizes any residual torsional forces and gives pure tension forces. i.e.: no twisting of the fastener - just straight spring force.

    This is why you press on your rim when you are truing. It relieves the torsion on the spokes.

  57. #57
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    Quote Originally Posted by Uncle Six Pack View Post
    Torque should not be thought of as a measure of friction (friction is a result, not a cause, of proper torquing).

    Torque is a measure of ROTATING force. Twisting force plus the simple machine we call a screw (or bolt) creates clamping force (rotating force becomes linear force).
    However you think it should be thought of, friction is the only thing opposing the force applied at the torque wrench and that is exactly what the torque wrench establishes.
    As I mentioned, what you are after is clamping force (the "preload" the other poster describes), and the relationship between measured torque and preload is dictated by the things that affect friction (i.e. lubricants on any contact surface of the fastener).
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  58. #58
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    Quote Originally Posted by meltingfeather View Post
    However you think it should be thought of, friction is the only thing opposing the force applied at the torque wrench...
    Then you clearly don't understand how a bolt works. Even in the complete absence of friction, it would be possible to torque a bolt properly (albeit to a lower value than in non-frictionless bolt). The friction just keeps it from backing off.

    But you are correct in most other things you said.
    You better just go ahead and drop that seatpost down to the reflector... the trail gets pretty rough down there.

  59. #59
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    Quote Originally Posted by Uncle Six Pack View Post
    Then you clearly don't understand how a bolt works.
    Clearly.
    Popped that one off too quickly. Friction is an important factor, but not the only one, as you point out.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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