zipp wheels stress relieving
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  1. #1
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    zipp wheels stress relieving

    http://www.zipp.com/Support/AskJosh/...6/Default.aspx

    Here Zipp mentions use of a "wine press" to stress relieve and claims it is superior to hand methods. What do you think? They seem to have a lot of hype on their site.

  2. #2
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    If I understand correctly, they use their 'wine press' to do more than stress-relieve - it sounds like they stretch all the spokes to very near their yield point.

    Does it work? I haven't heard much about Zipps going out of true, so it seems to.

    Is it necessary? I doubt it.

    FWIW, I'm under the impression that Reynolds uses a similar method, although maybe not so extreme.
    I love the sound of cowbell in the morning.

  3. #3
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    I think that Damon Rinard started this method at Trek, and it is similar to the method of pressing down on the edges of the rim which builders have been doing forever... but the "wine press" method lends itself to production line work. The point is to increase the stress in the spokes to relieve residual stresses, and also bed them in. I doubt they punch set the heads and do manual aligning of the spokes at the hub, cross, and nipples ends though.

  4. #4

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    Quote Originally Posted by steel515
    http://www.zipp.com/Support/AskJosh/...6/Default.aspx

    Here Zipp mentions use of a "wine press" to stress relieve and claims it is superior to hand methods. What do you think? They seem to have a lot of hype on their site.
    Their method using the "wine press" is better than not stress relieving the spokes, but it is not the most effective way either. Unfortunately, this method attempts to stress-relieve all the spokes simultaneously. The problem is that if they applied enough force to achieve maximum stress-relieve for al the spokes all at the same time, it might collapse the rim. That's assuming a wheel with a large number of spokes. For a wheel with a smaller number of spoke (say 12 or so), then might be able to get away with doing all the spokes at the same time.

    The description of why this works is unfortunately wrong. Spokes do not "creep". The reason that spokes loose tension with initial use is due to seating of the spokes in the hub flange, and settling of the eyelets and nipples at the rim. If you've ever taken a wheel apart after it has been used, there are indentations in the flange holes from where the spokes lay. It is primarily the formation of the indentations that cause the spokes to loose tension, not the spokes "creepiing". In order to prevent loose of tension in use due to these indentation, the indentations can be formed during the building the process by momentarily over-loading the spokes. That is what the "wine press" attempts to accomplish.

    There are other, better ways to do this operation. Holland Mechanics, which makes large automatic wheel building machines, has a machine to do this operation automatically, which it calls a "wheel stabilizer". It probably does a better job than the "wine press".

    Quote Originally Posted by bopApocalypse
    If I understand correctly, they use their 'wine press' to do more than stress-relieve - it sounds like they stretch all the spokes to very near their yield point.
    That's what stress-relieving is: Taking the spokes to very close to their yield point, to relieve points of localized "locked-in" high stresses. Spokes are extensively cold worked during their manufacture, and these cold working operations can result in internal "locked in" stresses - the forming operation leaves internal compressive and tensile static stresses. When these internal static stresses are combined with the spoke tensiong from building, they can result in localized points of very high stresses, which can be origin of fatigue cracks. When the spoke is momentarily loaded to just below its gross yield stress, the areas with "locked in" stresses can actually exceed their yield point, and plastically stretch. When the momentary over load is released, this points of locked in stresses that have yielded will return to a lower static stress state, and thus be less likely to form fatigue cracks.

    Quote Originally Posted by rruff
    I think that Damon Rinard started this method at Trek, and it is similar to the method of pressing down on the edges of the rim which builders have been doing forever... but the "wine press" method lends itself to production line work.
    Actually, the Trek method is a little bit different, and superior to the Zipp method. In the Trek method, the wheel is placed over a round hole on a table, the hole being a little bit smaller than the rim, so that the rim is evenly supported around its entire circumference by the edge of the hole. A "ram" then comes down and presses against the axle to provide the momentary overload on the rim. The reason that this method is better is because it allows a higher load to be delived to each spoke without the danger of collapsing the rim. As the ram pushes on one end of the hub, the tension in the spokes on the opposite side (below the arm) is increased, while the tension of the spokes on the opposite side are decreased by the same amount. By this method there is little change in the total compressive load on the rim, plus the rim is laterally supported all around, so the spokes can be loaded to a much higher momentary tension than with the "wine press" method. The disadvantage is that the wheel must be loaded twice, once from each side.

    To tell you the truth, I think the "old fashioned" method of squeezing pairs of spokes on opposite sides of the wheel is better than the "wine press" method, as it allows higher individual spoke loads, and therefore more stress-relieving action.

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