|
Spoke breaking repeated again and again
I got a relatively like new older wheel. My guess is that it was probably a machine built wheel laced with straight guage stainless spokes and I believe alloy nipples...I know brass is better but that is what they came with.
The wheel had only one spoke broken to begin with. Being curious I squeezed the pairs of spokes with my hands and had three spokes pop. Suppose I have my shop replace all three spokes and re-tension/true the wheel. Will I be in good shape? The mileage on the wheel seems very low. |
Originally Posted by SoreFeet
(Post 6627108)
I got a relatively like new older wheel. My guess is that it was probably a machine built wheel laced with straight guage stainless spokes and I believe alloy nipples...I know brass is better but that is what they came with.
The wheel had only one spoke broken to begin with. Being curious I squeezed the pairs of spokes with my hands and had three spokes pop. Suppose I have my shop replace all three spokes and re-tension/true the wheel. Will I be in good shape? The mileage on the wheel seems very low. Something doesn't sound right, for three spokes to break as you squeezed with your hands. I'd have the entire wheel relaced and built using the same hub and rim. |
First of all, how much is this wheel worth? It sounds like it's a cheap entry level wheel that you can get a replacement for less than $50. It is not worth the time or labour to rebuild a **** hub.
On the other hand if you have say, a chris king hub on a nice rim, it's probalby worth rebuilding. Just to give you an idea where you stand money wise. |
Originally Posted by SoreFeet
(Post 6627108)
Suppose I have my shop replace all three spokes and re-tension/true the wheel. Will I be in good shape?
|
Repeated spoke breaking is a sign of uneven tension. Get the whel to someone with a tensionmeter.
|
if tis a cheap ars wheel doesnt even worth to be sent to the shop because they will ask you probably 50 bucks for the job and probably the whole wheel costs less than that.
|
Originally Posted by capwater
(Post 6627663)
Repeated spoke breaking is a sign of uneven tension. Get the whel to someone with a tensionmeter.
|
If the rim is old enough it could have been one of a huge bunch that left China with bad spokes. There was quite a problem with wheels built for OEMs with a bad batch of spokes. Saw one in the LBS just today
|
When I get a bike that I am parting out, I often take the spokes off the wheels and save them. This is just about the only way you can justify replacing multiple spokes on a wheel - doing it yourself with low-cost parts. If you have to rely on the shop to replace spokes, it is a money losing proposition.
Chances are the wheel was damaged by some kind of trauma. Check to see if it is round. If the wheel is not round, you will be replacing spokes often. |
Originally Posted by SweetLou
(Post 6627801)
Multiple spoke breakage is a sign of fatigue, not uneven tension. You could have even low tension and get metal fatigue, you could have even high tension with a bad spoke line and get fatigue. If the spokes were not stressed relieved, you will get fatigue.
|
Originally Posted by TurboTurtle
(Post 6628917)
How can stress relieving reduce fatigue? - TF
FWIW I don't think that shift cables stretch either. I think that what we percieve as cable stretch is actually due to the cable housing seating itself in the ferrules and cable stops. |
Originally Posted by Retro Grouch
(Post 6628977)
I'm not convinced that "stress relieving" is an accurate term. I suspect that what really happens is the process seats the elbow end in the hub. If you don't do it the spoke will seat itself eventually through use but it will also cause the spoke to lose tension.
FWIW I don't think that shift cables stretch either. I think that what we percieve as cable stretch is actually due to the cable housing seating itself in the ferrules and cable stops. If the heads are set with a spoke punch when the wheel is built, they should be stable. Some call the spoke unwinding (the pings) 'stress relief' though that is really something entirely different. TF |
Originally Posted by TurboTurtle
(Post 6629231)
Stress relieving does seem to be real. The metal in the spokes has an elasticity that allows it to stretch. However at any tension, some of these elastic bonds will no longer return. Stress relieving puts more tension on the spoke than it will ever see in use and pre-breaks most of the non-elastic bonds.
Wow! I guess every engineering book on 'strength of materials' will now need to have a chapter added. Sarcasm aside, your explanation is simply wrong. |
I remember years ago I had a bike, a Fuji, I think. The spokes kept breaking. Turns out they were inserted into the spoke holes backwards.
|
Originally Posted by dwood
(Post 6629248)
Wow! I guess every engineering book on 'strength of materials' will now need to have a chapter added. Sarcasm aside, your explanation is simply wrong.
|
Originally Posted by TurboTurtle
(Post 6628917)
How can stress relieving reduce fatigue? - TF
Stress relieving will increase the spoke stress beyond the yield point, but only in the part of the spokes that are at the yield point. These parts will deform plastically and take a permanent set. When the stress relief force is removed, the spoke does not spring back and it will relax to a lower stress. Since the microscopic parts of the spoke that were at its yield point are no longer at their yield point the fatigue life is greatly increased. |
Originally Posted by Retro Grouch
(Post 6628977)
I'm not convinced that "stress relieving" is an accurate term. I suspect that what really happens is the process seats the elbow end in the hub. If you don't do it the spoke will seat itself eventually through use but it will also cause the spoke to lose tension.
FWIW I don't think that shift cables stretch either. I think that what we percieve as cable stretch is actually due to the cable housing seating itself in the ferrules and cable stops. You are correct about cables not stretching, but it isn't the housing seating itself. It has to do with the way cables are made. The extra tension on the cables will cause the cables' weave to settle into place, causing a tighter weave. The pre-stretched cables have done this weave tightening for you. |
I think what you people are talking about here is a well-known phenomenon in materials science known as work hardening.
A metal stressed beyond the yield point will plastically deform and increase in yield strength. Cold-working improves certain mechanical properties, such as fatigue life and hardness, but generally the material as a whole becomes more anisotropic from deformed grains : you gain properties in one direction at the expense of properties at, say, a right angle to it. What turtle said about how at any stress some parts of the metal are not elastic, is true. That is, the vast majority of the metal is elastic below the yield stress, but a tiny fraction of it isn't and will plastically deform. This is known as elastic hysteresis loss, and accounts largely for the reason why springs will stop bouncing under a mass even under perfect vacuum. |
I'm not. Spokes are work hardened, but stress relieving is not work hardening. It is the relieving of the residual stress of the spoke from manufacturing.
|
It is really a misnomer when someone says they 'stress relieve' a spoke. When you squeeze adjacent spokes together, or press on the rim, or any number of other ways to 'stress relieve' spokes, you are not changing the metallurgy of the spoke one iota. Stress relieving most metals involves heating them to an elevated temperature, allowing them to 'soak' at that temp for a specific length of time, and then letting them return to room temperature, usually slowly.
What is really happening with bicycle spokes it that they are trying to reach the shortest distance between the rim and hub. The end at the hub seats itself. The nipple seats itself in the rim. Any twist in the spoke [due to friction between the spoke and the nipple when it is tightened] is allowed to unwind itself by either the nipple turning in the hub or the spoke unscrewing itself from the nipple. Once this is done the spoke is stable. A spoke normally tightened never reaches it plastic region. |
Originally Posted by dwood
(Post 6630279)
It is really a misnomer when someone says they 'stress relieve' a spoke. When you squeeze adjacent spokes together, or press on the rim, or any number of other ways to 'stress relieve' spokes, you are not changing the metallurgy of the spoke one iota. Stress relieving most metals involves heating them to an elevated temperature, allowing them to 'soak' at that temp for a specific length of time, and then letting them return to room temperature, usually slowly.
What is really happening with bicycle spokes it that they are trying to reach the shortest distance between the rim and hub. The end at the hub seats itself. The nipple seats itself in the rim. Any twist in the spoke [due to friction between the spoke and the nipple when it is tightened] is allowed to unwind itself by either the nipple turning in the hub or the spoke unscrewing itself from the nipple. Once this is done the spoke is stable. A spoke normally tightened never reaches it plastic region. You are correct that a normally tightened spoke doesn't reach its yield limit, but parts of the elbow are at its yield point due to the bending during manufacturing. This is what you are trying to get rid of. If the elbow is not stress relieved, it will remain at its yield point, reducing fatigue life. Once this residual stress is removed, then a tensioned spoke is not at its yield point. This is why a properly stress relieved spoke that is tensioned adequately will last a very long time, longer than the rim will last. |
Originally Posted by SweetLou
(Post 6630357)
That is also not stress relieving. You are setting the spoke line That is different than taking a spoke beyond its yield point so that it plastically deforms.
You are correct that a normally tightened spoke doesn't reach its yield limit, but parts of the elbow are at its yield point due to the bending during manufacturing. This is what you are trying to get rid of. If the elbow is not stress relieved, it will remain at its yield point, reducing fatigue life. Once this residual stress is removed, then a tensioned spoke is not at its yield point. This is why a properly stress relieved spoke that is tensioned adequately will last a very long time, longer than the rim will last. Absolutely wrong! When it was bent during manufacture the area of the bend 'did' exceed its yield point, allowing it to remain bent. But it doesn't 'stay' at its yield point just because it is bent. In fact, depending on the alloy, its yield point has now been raised in the area of the bend due to work hardening. No amount of dickin' around with squeezing, pushing, pulling on that spoke is going to stress relieve the metal in that spoke. |
Originally Posted by dwood
(Post 6630442)
Absolutely wrong! When it was bent during manufacture the area of the bend 'did' exceed its yield point, allowing it to remain bent. But it doesn't 'stay' at its yield point just because it is bent. In fact, depending on the alloy, its yield point has now been raised in the area of the bend due to work hardening. No amount of dickin' around with squeezing, pushing, pulling on that spoke is going to stress relieve the metal in that spoke.
Originally Posted by Jobst Brandt
Spokes are cold formed. After cold forming steel always springs back a certain
amount. The spring-back is incomplete because part of the material went beyond its elastic limit and part did not. These disparate parts are fighting each other, and when spokes are tensioned, one or the other of these elements will be stressed additionally. This stress can be, and often is, at the yield stress and must be relieved when the wheel is completed. After correcting the spoke line, and when the wheel is true and tensioned, its spokes may appear to be in perfect alignment. However, some of the spokes have a good line at the elbow and rim only because they are tensioned. Besides, spokes have residual stresses at their elbows, heads, and threads from their forming process. As the wheel was laced the spokes may have been bent to make them conform to the hub and nipples. Since they were brought to their yield stress to bend them into place, the addition of tension guarantees that they remain at the yield point. When stressed to near their yield point, spokes have a short fatigue life. These stresses must be relieved to make the wheel durable. HOW STRESS RELIEVING WORKS Stress relieving can be regarded as correcting the spoke line at a microscopic level. The process momentarily increases spoke tension (and stress) beyond the yield point, but only in the parts of the spoke that are near yield. At the high stress points the spoke will deform plastically and take a permanent set. When the stress relief force is removed these areas cannot spring back, having, in effect, lost their memory, and relax to a lower stress. |
Originally Posted by dwood
(Post 6630279)
It is really a misnomer when someone says they 'stress relieve' a spoke. When you squeeze adjacent spokes together, or press on the rim, or any number of other ways to 'stress relieve' spokes, you are not changing the metallurgy of the spoke one iota. Stress relieving most metals involves heating them to an elevated temperature, allowing them to 'soak' at that temp for a specific length of time, and then letting them return to room temperature, usually slowly.
What is really happening with bicycle spokes it that they are trying to reach the shortest distance between the rim and hub. The end at the hub seats itself. The nipple seats itself in the rim. Any twist in the spoke [due to friction between the spoke and the nipple when it is tightened] is allowed to unwind itself by either the nipple turning in the hub or the spoke unscrewing itself from the nipple. Once this is done the spoke is stable. A spoke normally tightened never reaches it plastic region. |
No, dwood is saying that a spoke does not go beyond yield once it is tensioned in a wheel. There is elastic stretching. This is true and nothing will cause a plastic deformation. A plastic deformation will only happened if something hits the spokes, like your derailer or if the rim fails and tacos.
|
Originally Posted by SweetLou
(Post 6630933)
No, dwood is saying that a spoke does not go beyond yield once it is tensioned in a wheel. There is elastic stretching. This is true and nothing will cause a plastic deformation. A plastic deformation will only happened if something hits the spokes, like your derailer or if the rim fails and tacos.
A suggestion for T-Turtle: don't believe everything you read that has been written by 'bicycle experts' even if they claim to be engineers. I suggest you do some independent study in the Mechanical Engineering field. |
Originally Posted by SweetLou
(Post 6630933)
No, dwood is saying that a spoke does not go beyond yield once it is tensioned in a wheel. There is elastic stretching. This is true and nothing will cause a plastic deformation. A plastic deformation will only happened if something hits the spokes, like your derailer or if the rim fails and tacos.
|
There is some. Have you ever taken out a spoke and it has a bend in it? That is a plastic deformation. But I was saying that stress relieving does cause some plastic deformation (disputed by dwood). Once the wheel is built and tensioned, there should be no more plastic deformation.
I also meant that there is no normal force that will cause a plastic deformation. Once a wheel is built, the spoke will only plastically deform from some outside force, like a stick in the spokes. |
| All times are GMT -6. The time now is 05:44 AM. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.