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#41
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The Basics of Wheel Alignment and Wheelbuilding
On Sun, 01 Aug 2004 19:03:14 -0700, jim beam
wrote: his "stress relief" theory on the other hand is entirely subjective, Can you suggest some ways such a theory might be tested? |
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#42
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The Basics of Wheel Alignment and Wheelbuilding
jim beam wrote:
Mark McMaster wrote: jim beam wrote: wrote: snip Spoke-squeezing is an intriguingly mysterious subject to research. I remain agnostic, wavering one way and the other, but haven't seen any experimental data or analyses involving bicycle spokes. If you have the 3rd edition, perhaps you could peek at the Wiedemer stuff and give me your thoughts on it? you may also want to consider this question: q: elevator safety certification requires loading the cab to double it's "safe working load". this is to test the wire ropes that suspend it. the reason is that fracture mechanics predict that this process will typically reveal by failure any latent flaws. but, if we extend spoke squeezing theory, wouldn't this overload procedure also prevent fatigue of elevator cables? a: no. elevator cables still fatigue and need regular testing, inspection & replacement. This proves nothing one way or the other about the affects of squeezing spokes to reduce residual stress. There is no question that reducing residual (tensile) stresses can increase fatigue life. There is also no question that spokes (or elevator cables) will still fatigue if the cyclic load is high enough (i.e. above the endurance limit). The question is whether squeezing the spokes provides any significant beneficial reduction in residual stress, or increases the endurance limit. Mark McMaster ah, this explains everything! stainless steel has been developed that has an endurance limit! and it's used in bicycle spokes!!! no. this is one of the fundamental flaws of "the book". it cites material behavior for mild steel, which /does/ have an endurance limit, and then presumes to describe behavior in stanless steel, which does not. just exactly how this lends credibility to a revolutionary means of eliminating metal fatigue is something i have yet to come to terms with. Ah, as usual, you dodge the question rather than addressing it. Whether or not a material has a true endurance limit or not doesn't change the question of whether momentarily overloading the spokes can reduce residual stress and/or increase fatigue life, which is central to the argument. But then, you appear to be far more interested in being a contrarian than to actually knowing what is going on. That momentarily overloading the spokes results in increased spoke life has been reported by many sources. Not just here in the RBT newsgroup but by others as well, both inside and outside the industry. For example, here is the Bontrager wheel manual which shows how their "wheel stressor" is used to momentarily overload the spokes: http://www.bontrager.com/workshop/do...eel_manual.pdf So, just what is the mechanism that causes the spokes to have improved fatigue life after momentarily overloading them? If you do not believe that Brandt is correct about relieving residual stresses in the spokes, than what other explanation do you propose? And about stainless steel having an endurance limit: Whether any material has a true and absolute endurance limit is often debated. However, under a common usage of the term (fatigue strength at 10^7 cycles is a common definition), the types of stainless steel used in spokes does have an endurance limit (but then, you probably knew that). We can dispose of that red herring. Here are some data on some stainless steels of the type used in spokes (for example, Wheelsmith uses 304, DT uses 18-8), including their endurance limits: http://www.hghouston.com/ss_cwp.html http://www.band-it-idex.com/pdfs/sta...el/302_305.pdf http://www.askzn.co.za/tech/tech_grade_304.htm Mark McMaster |
#43
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The Basics of Wheel Alignment and Wheelbuilding
Trevor Jeffrey wrote:
Tim McNamara wrote in message ... oil. My spoke nipples do not unwind in use, despite being 215 lbs and riding 32 spoke wheels 6,000 to 7,000 miles a year. The reason for this is not using something to glue the nipples and spokes together, but using adeqate tension in the first place. Stuff like linseed oil and Spoke Prep just covers for a badly built wheel. Hmmm, this conversation seems like old times. The use of any oil will assist in the prevention of a nipple shaking loose, a drying oil just happens to be the most successful in this application, i.e. a wheel not overtensioned. The wheel construction is how I describe and not what you ride. Your conversation is repeated because you do not appear to take on board what I have wrote. Adequate tension is accomplished when the wheel remains laterally stable under load. Further tension unnecessarily reduces the available load capacity of the rim and so of the wheel. Sorry, it doesn't work this way. Because the spokes are far stiffer than the rim, very little of the load is supported by the rim at all when the wheel is loaded - at least not until the spokes go slack. But then the wheel losses the lateral stability you seek, so asking the rim to support the load is a poor idea. Mark McMaster |
#44
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The Basics of Wheel Alignment and Wheelbuilding
On Sun, 01 Aug 2004 21:45:24 -0500, dianne_1234
wrote: On Sun, 01 Aug 2004 19:03:14 -0700, jim beam wrote: his "stress relief" theory on the other hand is entirely subjective, Can you suggest some ways such a theory might be tested? Dear Dianne, One way would be to take before and after pictures that either do or do not show microscopic changes in a squeezed spoke. (My understanding of such matters is so feeble that I should add that "microscopic" may need to be replaced by "x-ray diffraction" or even more exciting technologies involving terms like "lattice" and "crystal" and "scanning microscope"--or possibly "bi-focals.") Unfortunately, this requires more than just swiping a spoke across the bar-code reader at the grocery store, so I've stopped holding my breath while waiting for such evidence to appear. Another test would be to find an industry in which a very similar process has been developed and tested. The obvious place to look would be spoked motorcycle wheels, or even the spoked wheels of obsolete British sports cars. There might be a paper detailing testing of spoke stress-relief lurking out there somewhere. (If none can be found, this is not proof that the theory is wrong--spokes in other applications might be so over-engineered that stress-relief is pointless, or the wheels elsewhere might just be badly built.) A practical test would involve taking several brands of modern spokes and subjecting batches of them to some Rube Goldberg machine that mimics the rapid reduction of otherwise steady tension in a rolling bicycle wheel for millions of cycles. If the stress-relieved batch outlasted the unsqueezed batch, it would settle the matter. Because the subject is of little interest outside rec.bicycles.tech, expensive and serious testing beyond anecdote is unlikely. Perhaps someone will find a peer reviewed paper on spokes (as opposed to related but arguably different matters), but I expect that it would have turned up by now if such a study existed. (Again, the absence of a study is not proof for or against the theory--and the Wiedemer citation that I assume appears in the 3rd edition of "The Bicycle Wheel" might be specifically on spokes. I take comfort in the fact that I'm apparently not the only member of rec.bicycles.tech too cheap to buy the newer edition.) A less expensive (and less conclusive) test would be to find a large group of dedicated bicyclists unaware of the spoke squeezing theory and find out how often their spokes break. The only group that I can think of that might fit this description would be the Keirin racers of Japan, but it wouldn't surprise me if they've thoughtlessly heard of the stress-relief theory and ruined themselves as a control group. In any case, we could only compare such a group to a very small, self-selected group here on rec.bicycles.tech. A double-blind study is hard to arrange when there's little interest and the testing is expected to take a long time. One test that occurred to me is to find out what the spoke squeezing theory predicts will happen to unsqueezed spokes. Obviously, unsqueezed spokes are supposed to fatigue and fail sooner than apparently immortal squeezed spokes, but how much sooner? That is, given 72 spokes on a pair of wheels built as similarly as possible, except for the spoke squeezing, how many will break in each set of wheels in ten, twenty, fifty, or a hundred thousand miles of similar riding? I haven't seen any such predictions, but making them might help put the debate in perspective. My impression is that those who doubt the theory would predict no significant difference in spoke failure rates. I have no idea what kind of failure rates would be predicted for unsqueezed spokes by spoke-squeezing proponents, but it would be fascinating to see what kind of predictions would be made and how they would be supported. Time to see how my troop of monkeys is doing on duplicating the First Folio. Carl Fogel |
#45
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The Basics of Wheel Alignment and Wheelbuilding
Mark McMaster Wrote:[color=blue] jim beam wrote: So, just what is the mechanism that causes the spokes to have improved fatigue life after momentarily overloading them? If you do not believe that Brandt is correct about relieving residual stresses in the spokes, than what other explanation do you propose? And about stainless steel having an endurance limit: Whether any material has a true and absolute endurance limit is often debated. However, under a common usage of the term (fatigue strength at 10^7 cycles is a common definition), the types of stainless steel used in spokes does have an endurance limit (but then, you probably knew that). We can dispose of that red herring. Here are some data on some stainless steels of the type used in spokes (for example, Wheelsmith uses 304, DT uses 18-8), including their endurance limits: http://www.hghouston.com/ss_cwp.html http://www.band-it-idex.com/pdfs/sta...el/302_305.pdf http://www.askzn.co.za/tech/tech_grade_304.htm Mark McMaster The 300 series of stainless steels are 18-8 stainless steels with slight modifications between the different numbers. Since the 300 series is an AISI designation, European and other areas are not obliged to call them with this designation. These stainless steels are all austenitic, meaning they have no ferromagnetic properties in their annealed state. Plastic deformation changes this structure to partially ferritic structure making highly cold worked stainless steels (with some exceptions like 316, a molybdenum modification of 18-8) slightly magnetic. In addition, this crystaline change greatly increases the yield strength and is HIGHLY ansitropic in its effects. The overstressing procedure forces changes in the elbow, causing it to conform to the flange hole AND causing deformation of the flange hole itself. Because of this, the stresses of the bend is now spread over a longer range of the bend. Cyclic loading consistent with riding is now operating this joint in a purely elastic range rather than exposing tiny areas of the bend to very high stresses over very small areas. This is no different than some pressure vessel codes (notably French, I forget the code) that hydrostatically test pressure vessels at much higher pressures than the design. This is termed "auto frettage" and confers much higher cyclic life to the vessel. -- Weisse Luft |
#46
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The Basics of Wheel Alignment and Wheelbuilding
On Mon, 02 Aug 2004 03:28:58 GMT, Mark McMaster
wrote: jim beam wrote: Mark McMaster wrote: jim beam wrote: wrote: snip Spoke-squeezing is an intriguingly mysterious subject to research. I remain agnostic, wavering one way and the other, but haven't seen any experimental data or analyses involving bicycle spokes. If you have the 3rd edition, perhaps you could peek at the Wiedemer stuff and give me your thoughts on it? you may also want to consider this question: q: elevator safety certification requires loading the cab to double it's "safe working load". this is to test the wire ropes that suspend it. the reason is that fracture mechanics predict that this process will typically reveal by failure any latent flaws. but, if we extend spoke squeezing theory, wouldn't this overload procedure also prevent fatigue of elevator cables? a: no. elevator cables still fatigue and need regular testing, inspection & replacement. This proves nothing one way or the other about the affects of squeezing spokes to reduce residual stress. There is no question that reducing residual (tensile) stresses can increase fatigue life. There is also no question that spokes (or elevator cables) will still fatigue if the cyclic load is high enough (i.e. above the endurance limit). The question is whether squeezing the spokes provides any significant beneficial reduction in residual stress, or increases the endurance limit. Mark McMaster ah, this explains everything! stainless steel has been developed that has an endurance limit! and it's used in bicycle spokes!!! no. this is one of the fundamental flaws of "the book". it cites material behavior for mild steel, which /does/ have an endurance limit, and then presumes to describe behavior in stanless steel, which does not. just exactly how this lends credibility to a revolutionary means of eliminating metal fatigue is something i have yet to come to terms with. Ah, as usual, you dodge the question rather than addressing it. Whether or not a material has a true endurance limit or not doesn't change the question of whether momentarily overloading the spokes can reduce residual stress and/or increase fatigue life, which is central to the argument. But then, you appear to be far more interested in being a contrarian than to actually knowing what is going on. That momentarily overloading the spokes results in increased spoke life has been reported by many sources. Not just here in the RBT newsgroup but by others as well, both inside and outside the industry. For example, here is the Bontrager wheel manual which shows how their "wheel stressor" is used to momentarily overload the spokes: http://www.bontrager.com/workshop/do...eel_manual.pdf So, just what is the mechanism that causes the spokes to have improved fatigue life after momentarily overloading them? If you do not believe that Brandt is correct about relieving residual stresses in the spokes, than what other explanation do you propose? And about stainless steel having an endurance limit: Whether any material has a true and absolute endurance limit is often debated. However, under a common usage of the term (fatigue strength at 10^7 cycles is a common definition), the types of stainless steel used in spokes does have an endurance limit (but then, you probably knew that). We can dispose of that red herring. Here are some data on some stainless steels of the type used in spokes (for example, Wheelsmith uses 304, DT uses 18-8), including their endurance limits: http://www.hghouston.com/ss_cwp.html http://www.band-it-idex.com/pdfs/sta...el/302_305.pdf http://www.askzn.co.za/tech/tech_grade_304.htm Mark McMaster Dear Mark, I'm pleased to see the Bontrager stressor tool, which does indeed show a serious attempt to calibrate how much the spokes are being stretched. Thanks for the link. Being hopelessly contrarian even when wavering on the fence, however, I have to ask if that same link proves that Jobst is mistaken about paired spokes being antiquated nonsense? That is, yes, they make a very nice tool for stretching spokes, but the question is what the effect is of stretching spokes, not how precisely it can be done. That people have reported increased spoke life is true, but the question is whether their reporting is accurate. They may be quite right, but they may also be replicating the tying and soldering reports that Jobst's testing demolished. Do you know of any formal studies showing that squeezed or stretched spokes enjoy a longer life? I'm sure that Bontrager believes it, just as I'm sure that Jobst and others believe it. Unfortunately, it's a difficult matter to resolve either way because any physical change in an actual spoke would probably be on such a microscopic level that it would very expensive to photograph and any statistically significant testing might be frighteningly tedious. Again, the lack of testing is not evidence that the theory is wrong, just an indication of how beastly difficult it may be: "The fatigue resistance of spokes was not tested for lack of suitable equipment." --"The Bicycle Wheel," 2nd edition, Part III, "Equations and Tests" It's worth pointing out that those who deny the spoke squeezing theory seem to be in the same boat in that their testing is at least as anecdotal, leaving laymen like me to admire all the fury and theory and to incline to agree with whichever post I read last. I suspect that the spokes don't care how much we abuse each other and that they simply fatigue in a pattern that I haven't yet seen documented. Some day, if I'm lucky, someone will rub my nose in a knock-down, indisputable study, crow about how the testing proves that their arguments were correct, sneer at my wishy-washiness, and win my Fury RoadMaster as a prize. Carl Fogel |
#47
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The Basics of Wheel Alignment and Wheelbuilding
On Mon, 2 Aug 2004 13:58:26 +1000, Weisse Luft
wrote: [snip metallurgy] The overstressing procedure forces changes in the elbow, causing it to conform to the flange hole AND causing deformation of the flange hole itself. Because of this, the stresses of the bend is now spread over a longer range of the bend. Cyclic loading consistent with riding is now operating this joint in a purely elastic range rather than exposing tiny areas of the bend to very high stresses over very small areas. This is no different than some pressure vessel codes (notably French, I forget the code) that hydrostatically test pressure vessels at much higher pressures than the design. This is termed "auto frettage" and confers much higher cyclic life to the vessel. Dear Weisse, Forgive my layman's summary of what seems rather clear, but I want to be sure that I'm following you. You agree with the spoke-squeezing side of the debate that overstressing significantly increases spoke life, but you believe that it has nothing to do with internal stress relief and is instead a matter of a better mechanical mating of the spoke elbow with the hub hole that spreads the load out and greatly reduces the stress? If so, would magnified before and after pictures of the hub hole show a difference? I have a vague notion that you've mentioned scuba equipment in passing. Is that what you have in mind when you speak of pressure vessels? I'm hoping to wander off into "auto frettage," but can't figure out how it resembles the spoke hole and elbow situation. Thanks, Carl Fogel |
#48
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The Basics of Wheel Alignment and Wheelbuilding
Tim McNamara wrote:
The type of guttersniping you indulge in does not advance the discussion one whit. Over the years we've had recurrent posters with the gunslinger mentality who come into town aiming to knock off the big guy. You seem to be just another one of this species. I suspect that many of those posters have been the same person hiding behind different personae, due to consistencies in writing style and conceptual framework. You don't raise chickens, by any chance? Er, we already know that "jim beam" is a sock puppet for "tux lover", a persona retired when it acquired too much of a reputation as a nut case. That cannot be far away for "jim beam", since as far as I can see if Brandt posted that wheels are round and spokes are thin it would net another dose of froth. -- David Damerell Distortion Field! |
#49
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The Basics of Wheel Alignment and Wheelbuilding
Mark McMaster wrote in message ... Sorry, it doesn't work this way. Because the spokes are far stiffer than the rim, very little of the load is supported by the rim at all when the wheel is loaded - at least not until the spokes go slack. But then the wheel losses the lateral stability you seek, so asking the rim to support the load is a poor idea. To what you are referring does not work I cannot make out. The spokes are tensile members so need to be resistive to stretch and the rim is a compressive member so needs to be resistive to squash. One is the complete opposite of the other. The two are not comparable to each other. Aluminium is good in compression but not in tension, this is the way of the world, aluminium rims and steel spokes. If the rim did not support the load it would not need to be there. It either does or it does not, extraneous items are most usually omitted on a human powered vehicle. Rims are essential part of the wheel and bear all the load. What else could possible transmit the force between tyre and spokes? TJ |
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The Basics of Wheel Alignment and Wheelbuilding
Mark McMaster wrote in message ... So, just what is the mechanism that causes the spokes to have improved fatigue life after momentarily overloading them? Shaping the spoke at the crossing point reduces lateral movement at the crossing causing angular displacement at the hub with the resultant early spoke failure due to fatigue. Overtensioning the spokes goes someway to achieving this unintentionally. TJ |
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