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Thread: Stress relief

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    Team Water Andy_K's Avatar
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    Stress relief

    So, when I'm stress relieving a wheel using the method of squeezing pseudo-parallel spokes, how hard do I need to squeeze?

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    Type 1 Racer rydaddy's Avatar
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    Hard enough to hurt... with gloves on.

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    Easier and better method to stress relieve is by putting wheel on the floor on the axle end and gently pushing with both arms on opposite sides of the rim until you just feel it giving. Rotate and repeat, flip and repeat.
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    Quote Originally Posted by rydaddy View Post
    Hard enough to hurt... with gloves on.
    So for someone like me who lacks Kung Fu Grip(TM), just about as hard as I can squeeze?


    Quote Originally Posted by San Rensho View Post
    Easier and better method to stress relieve is by putting wheel on the floor on the axle end and gently pushing with both arms on opposite sides of the rim until you just feel it giving. Rotate and repeat, flip and repeat.
    Hmm... I just tried that. I put as much of my 195 pound girth on it as I could while still using my toes for balance, and it didn't feel like it was giving at all. Should I have done this before bringing the tension up all the way?

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    Senior Member bikeman715's Avatar
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    no after the wheel is brought to it 's tension then stress it and re-true or bring the tension back up.
    bikeman715

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    Senior Member BCRider's Avatar
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    I like using a couple of lengths of hard wood dowel instead of my hands. I use them as levers with the end of the dowel under one crossing and the shaft laying over the next crossing towards me. I put one on each side at the same time and then lever inwards. This pushes the crossing sat the ends outwards and the crossings at the "fulcrum" inwards. I advance by one crossing pair and repeat until done. This way each crossing gets levered both in and out. It sets the bend at the cross overs and stresses the spoke heads hard enough to form well at the hubs.

    It seems to work well as I seldom need more than a light and very infrequent truing as the wheels age. And it's a LOT easier on the hands. I tried that for one wheel and decided that there had to be a better way.

    There's lots of stress relieving options that work just fine. My way is just one.
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    That sounds like what Sheldon Brown recommends. I had a hard time picturing it, in spite of his pictures, but I think I've got it now.

    The Jobst Brandt (spoke squeezing) method just seemed uncharacteristcally vague in his book. He tells you that doing this wrong is the cause of most wheel failures, and then he says to squeeze "hard".... I may be overthinking this, but I like things to be measurable when they're important.

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    I just lay the wheel on a carpet, then try and balance myself on the axle while standing on the rim.

    I'm only 60kg, so there's no problem with me doing this.
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    In general, pushing on opposite sides of the rim is adequate when stress relieving. Be sure to apply a minimum total force of 100 lbs. You should hear some spokes cracking at the beginning. Repeat this process till the wheel is true.

    I like to bring the spoke tension very close to the yield point of the rim. If I use the pry-bar technique to stress the spokes, then the rim may go into non-elastic deformation, especially with a low-priced thin-walled boxed rim.

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    There are two basic issues involved in what folks call stress relieving.

    The first is setting the bend at the elbows. Spokes are typically supplied with bends of 90° or slightly less. Therefore, on most hubs the spokes with elbows on the outside of the flange naturally lie at an angle outside of their final tight position, and have to be pulled inboard when laced, forming a curve. Even when tightened they are fighting their natural tendency to be more outboard. Squeezing all the spokes inward bends the elbows a few extra degrees setting them to the correct angle, and making the spoke seem to have lengthened a bit. It isn't a matter of how hard, but how far you push the outside toward the middle. You'll know by observing the line of the spokes as they leave the flange.

    The second purpose is to create a bit of overtension and with lighter spokes a bit of slack. This sets the nipples in the rim, and allows twisted spokes to untwist. You'll hear the untwisting as pinging, and since a spoke turning in a nipple is the same as turning the nipple, it'll call for a bit of touchup. If you don't do it now, you'll hear it on your first ride, and can touch up wheel afterward, which is OK for your own wheels but not if building for others.

    The various techniques described by others here all work, but some are better for one goal than the other, and I do both, setting the elbows fairly early on when it's easier, and flexing the rim as a near final step. It isn't a question of exactly how you stress relieve, but of knowing what your trying to achieve and using a method that works for you.
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    Quote Originally Posted by Andy_K View Post
    That sounds like what Sheldon Brown recommends. I had a hard time picturing it, in spite of his pictures, but I think I've got it now.

    The Jobst Brandt (spoke squeezing) method just seemed uncharacteristcally vague in his book. He tells you that doing this wrong is the cause of most wheel failures, and then he says to squeeze "hard".... I may be overthinking this, but I like things to be measurable when they're important.
    You may be overthinking this.

    THe only specific given by Jobst Brandt is to squeeze them 'hard,' so assume that the mistake people make that results in falure is that they do not squeeze hard enough.

    How hard? Real hard. Real real hard. Unless you know you are an unusually strong person (avid rock-climber or professional weighlifter or arm-wrestler) then you should squeeze just about as hard as you can.

    Then re-true and re-stress, and repeat until stressing does not require truing.

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    commuter TimeTravel_0's Avatar
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    block of wood
    place axle on wood
    push down on the rim with both hands with a good amount of force
    rotate the wheel like you're driving a bus until all sections of the rim has been pushed
    flip wheel over and repeat.

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    I'm no expert, but THIS link might help.

    He gives a couple of options for stress relief.

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    Senior Member DannoXYZ's Avatar
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    People are getting two different operations mixed up:

    bedding in nipples and elbows are done with an INCREASE in tension.

    stress relieving requires a DECREASE in tension to unwind the spokes that are stressed due to twisting while truing.

    Each one requires a different process, although some all-in-one procedures can partially stress-relieve a wheel. But the only real way to stress-relieve and unwind spokes is to bring the rim closer to the hub.

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    Quote Originally Posted by DannoXYZ View Post
    stress relieving requires a DECREASE in tension to unwind the spokes that are stressed due to twisting while truing.
    stress relieving requires an INCREASE in tension to take the parts of the spoke with high stress (especially the elbows) past their elastic limit since the number of fatigue cycles material survives depends on the average stress which would otherwise be high in areas of the spoke with residual stress like the elbows.

    Each one requires a different process, although some all-in-one procedures can partially stress-relieve a wheel. But the only real way to stress-relieve and unwind spokes is to bring the rim closer to the hub.
    You can only stress relieve by increasing spoke tension.

    Spoke windup can be avoided during the build process. A piece of tape on a representative spoke (one on each side of the wheel in back) will let you know how that spoke/nipple/tension/socket/lubrication combination is behaving.

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    Quote Originally Posted by Andy_K View Post
    That sounds like what Sheldon Brown recommends. I had a hard time picturing it, in spite of his pictures, but I think I've got it now.

    The Jobst Brandt (spoke squeezing) method just seemed uncharacteristcally vague in his book. He tells you that doing this wrong is the cause of most wheel failures, and then he says to squeeze "hard".... I may be overthinking this, but I like things to be measurable when they're important.
    Stress relieving is actually a real engineering term, but most people including professional wheel builders gets it completely wrong. Usually people confuse it with getting rid of spoke windup by eg. side loading the rim so the spokes loose tension and therefore may unwind. That however isn't stress relieving spokes. Here are some Jobst Brandt quotes on the subject:

    http://www.sheldonbrown.com/brandt/s...relieving.html
    http://yarchive.net/bike/stress_relieve.html

    Sheldon Brown method may work too if you got weak hands (don't scratch or kink the spokes though), but the squeezing method is the safest method since normal humans can't squeeze hard enough to cause any damage.

    How hard? Well, make an effort, don't be gentle or afraid you damage the wheel. Personally I use a towel and squeeze with both hands. In the one of the Usenet post linked above, JB writes that squeezing may raise the tension for the grabbed spokes between 50% to 100%. So if you stress relieve the spokes at 50 kgf (random number) they should be around 75 to 100 kgf when you squeeze. Not sure if a tensiometer can give proper results when squeezing, but the feeling of eg. around 100 kgf spoke can be gotten by squeezing a finished front wheel.

    --
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    aka Tom Reingold noglider's Avatar
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    Pressing on the rim will get rid of the twist in spokes but it doesn't serve the purpose of stress relief. Do not confuse these two things. Pressing on the rim gives a satisfying sound, and stress relieving does not.
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    Used to be Conspiratemus
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    ^Bingo. Another pithy post by Noglider that gets it right in few words.
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    aka Tom Reingold noglider's Avatar
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    Thank you, conspiratemus1. I don't normally like to pipe in when others have made the same point, but I thought I could convey it better by using fewer words.
    You don't read my signature anyway, do you?

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    Stress relieving by squeezing and prying apart the spokes may benefit an old wheel or low-mid spoke tension. The side-loading technique is much more effective when working with new quality rims and spokes, especially if the initial tolerances are set at +/-0.001" with high spoke tension.

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    Quote Originally Posted by DannoXYZ View Post
    People are getting two different operations mixed up:

    bedding in nipples and elbows are done with an INCREASE in tension.

    stress relieving requires a DECREASE in tension to unwind the spokes that are stressed due to twisting while truing.

    Each one requires a different process, although some all-in-one procedures can partially stress-relieve a wheel. But the only real way to stress-relieve and unwind spokes is to bring the rim closer to the hub.
    Stress relieving has nopthing to do with the unwinding of the spokes. It is to over load the spokes to take them past their yield point and relieve internal stresses from forming the spokes and building up a wheel.
    Last edited by davidad; 11-11-10 at 07:40 PM.

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