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#61
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The Basics of Wheel Alignment and Wheelbuilding
The spoke head will bed into an aluminium hub flange of its own accord.
Ride bike hard and nip up a little if found necessary. TJ Trevor Jeffrey wrote in message ... Peter Cole wrote in message 5PqPc.195614$a24.110765@attbi_s03... Practically speaking, whether momentary overloading increase spoke fatigue life by reducing residual manufacturing stresses or by "bedding in" the spoke/flange interface is immaterial, as long as it works, it's a procedure that should be followed. I do not believe that all constructors using the method of overtensioning spokes have had an equal benefit. As I have said previously, overtensioning, accidentally, partially forms the bend in the spoke at the crossing point so as to reduce the angular displacement at the hub during the cyclic variation of loading. With a reduced angular displacement at the hub interface the MTBF is increased due to the lowered rate of fatigue. The fatigue rate is primarily dependant upon the angular displacement and not the tensile force or variation in thereof. Relatively the momentary overloading is a waste of time compared to specifically shaping the spoke correctly. TJ |
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#62
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The Basics of Wheel Alignment and Wheelbuilding
Weisse Luft wrote in message ... That spoke takes a compressive load, manifested as a decrease in tension. And the wheel is under a compressive load from the sum of the sopke tensions but it also can take a tensile load, manifested by a reduction in the compressive stress. Please mind your language. A decrease in tension is not compression. It cannot be so. It is the rim which is under a compressive load and the spokes under a tensile load, it is therefore wrong to declare the whole wheel as under a compressive load. You are confused. TJ |
#63
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The Basics of Wheel Alignment and Wheelbuilding
Trevor Jeffrey Wrote: Weisse Luft wrote in message ... That spoke takes a compressive load, manifested as a decrease in tension. And the wheel is under a compressive load from the sum of the sopke tensions but it also can take a tensile load, manifested by a reduction in the compressive stress. Please mind your language. A decrease in tension is not compression. It cannot be so. It is the rim which is under a compressive load and the spokes under a tensile load, it is therefore wrong to declare the whole wheel as under a compressive load. You are confused. TJ No, I am not confused. If you know how to draw a free body diagram, you will see the error in your ways if you can accurately measure the rim deflection. Pretensioned structures easily confuse those who study them. Rest assured, a wheel stands on its spokes, be they wire, rope or pegs. -- Weisse Luft |
#64
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The Basics of Wheel Alignment and Wheelbuilding
"Weisse Luft" wrote in
message ... Peter Cole Wrote: " Practically speaking, whether momentary overloading increase spoke fatigue life by reducing residual manufacturing stresses or by "bedding in" the spoke/flange interface is immaterial, as long as it works, it's a procedure that should be followed. For the "bedding" theory to be correct, it would require that the bulk material in both the spoke and flange to be taken beyond yield. I don't think that's the recommended practice. Your version of "bedding", since it involves higher forces, would necessarily also perform the reduction of residual stresses, so the claim that it works by that particular mechanism would seem impossible to prove. In fact, those of us who don't stress relieve to yield, yet observe improved spoke lifetimes, would seem to have experiences which refute that theory. Yielding occurs only in a partial cross section of the spoke during the stress relieving process. Because the entire cross section does not go to yield, the tension can and does remain the same. Of course. But that's what's wrong with the "bedding" argument, it requires yield at the elbow and at the flange. |
#65
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The Basics of Wheel Alignment and Wheelbuilding
"Trevor Jeffrey" wrote in message ... Peter Cole wrote in message 5PqPc.195614$a24.110765@attbi_s03... Practically speaking, whether momentary overloading increase spoke fatigue life by reducing residual manufacturing stresses or by "bedding in" the spoke/flange interface is immaterial, as long as it works, it's a procedure that should be followed. I do not believe that all constructors using the method of overtensioning spokes have had an equal benefit. As I have said previously, overtensioning, accidentally, partially forms the bend in the spoke at the crossing point so as to reduce the angular displacement at the hub during the cyclic variation of loading. With a reduced angular displacement at the hub interface the MTBF is increased due to the lowered rate of fatigue. The fatigue rate is primarily dependant upon the angular displacement and not the tensile force or variation in thereof. Relatively the momentary overloading is a waste of time compared to specifically shaping the spoke correctly. I believe what you're concerned about is what Jobst Brandt describes as "improving the spoke line". The difference being that his concern is bends (loaded) at the flange and nipple, while you worry about the crossing. The concept seems the same, only the forces seem larger in the misalignments he describes. |
#66
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The Basics of Wheel Alignment and Wheelbuilding
Trevor Jeffrey:
Jose Rizal wrote in message ... Just how do you do this, and how do you account for the dynamic loads put on the wheel which exceed the static rider/bike weight? Put water into pan, light gas, place egg in water, bring to boil, turn off gas. It would help if questions were more spcific than how do you do this? specifically which part of my explanation do you think requires further explanation? The question followed your last statement "tighten to a point where the riders (sic) full weight does not releive (sic) the bottom spoke" immediately. It's not hard to figure out which part the question refers to. 7/5(rider+bike+load) Front wheel loading. Where does this magic figure come from? As another answer explains it is a simple matter to tension the wheel a bit more if the rider finds the wheel wobbly. Trial and error is what you're suggesting. What the hell is "a wheel which will fail safe"? Will not lock up in the frame due to buckling. There is no such thing. Buckling is largely dependent on the magnitude and direction of the load on the rim. A large enough load can buckle a wheel enough to wrap it around your fork. Since buckling is also load magnitude dependent, "severre" buckling cannot be avoided if the load is high enough, and especially since you only tensioned the spokes enough to take up your static weight. Spoke quality is not an issue. Plastic spokes will be fine then. Steel is an excellent material for bicycle spokes. Plastics are not renowned for their ability to work in tension and I doubt any plastic could replace the steel spoke. Aramid fibre of course is exceptionally strong and may provide an alternative at increased cost. Hence spoke quality is an issue. |
#67
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The Basics of Wheel Alignment and Wheelbuilding
jim beam:
Jose Rizal wrote: jim beam: it's only the practical issues of price, of needing a spoke that resists torque sufficiently to be able to tighten a nipple and indeed, ability to thread a nipple in the first place that lead to the use of single strand. This made-up story doesn't even look nor sound good. Spokes still do twist, and a threaded nipple is not the only way to have an adjustable tightening mechanism on a rim. what method do you propose? the threaded nipple method is cheap, reliable and has stood the test of time. and of course spokes still twist, but not as much as the equivalent multi-strand. brake cable's about the same as a spoke, try the comparision. This has nothing to do with the claim you made befo "it's only the practical issues of price, of needing a spoke that resists torque sufficiently to be able to tighten a nipple and indeed, ability to thread a nipple in the first place that lead to the use of single strand." Does it matter that they bend around pulleys in a constant side-to-side flexing different than spokes? yes, and those pulleys cause wear and bending stresses, but that's why you use multi-strand in the first place. Hence spokes and cable are not the same "application". maybe your definiton of tension is different to mine. Bending stresses do not result in only tension in cables or solid rods. One side will experience compression. You do not have this issue with spokes. also, one strand breaking in a rope of 100 leaves 99 others - pretty comforting. Nonsense. If a cable is loaded such that a strand breaks, the effective cross section of the cable is reduced and hence the load results in a higher stress for the remaining strands, which will rapidly lead to failure of the cable. If a strand was broken by other than a load (eg cut), the same effect on cross section will be observed. You can't cut a strand on a solid spoke. read some fracture mechanics. crack propagation in a single piece leads to failure of the whole. fracture of a single strand does not. Dodging again. Study some basic engineering. Fracture of a single strand in a cable decreases the load-bearing cross-section of the cable, which decreases the maximum load it can withstand. If the break happens because of a high enough load, the rest of the strands will experience higher stresses since there are less of them, and the cable will eventually fail. next time you fly, check out the skin of the plane and notice that it's made of many parts riveted together. is this because manufacturers can't weld? no, it's because crack proagation in one piece does not propagate to the whole - it's a policy of fracture containment. An absolutely ridiculous contention. A plane's skin is NOT a significant load bearing structure. The FRAME is. An airplane's skin is riveted for ease of manufacture, assembly and replacement. It has nothing to do with "fracture containment". So to you a cable = spoke = airplane skin. These are erroneous comparisons. and there's a small degree of freedom to move between strands which reduces cross sectional stress considerably. Again, nonsense. What can move between strands? The only way to move loads between strands is if the strands are able to move along the cable's length. This is a bad event since the strands will not take up the load evenly amongst themselves. take a cable and cut the end exactly square. then bend it about some kind of mandrel. notice how the end is no longer square and the strands are staggered? they move relative one to another. this is why rope is flexible. And so? The ends of elevator cables are not free; nor of any cables used in any load-bearing application. These are crimped/welded/looped together to prevent movement of the strands relative to each other. One of the reasons this is done is to ensure that the tensile load is shared equally amongst the strands. |
#68
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The Basics of Wheel Alignment and Wheelbuilding
Peter Cole wrote in message ... "Trevor Jeffrey" wrote in message ... I do not believe that all constructors using the method of overtensioning spokes have had an equal benefit. As I have said previously, overtensioning, accidentally, partially forms the bend in the spoke at the crossing point so as to reduce the angular displacement at the hub during the cyclic variation of loading. With a reduced angular displacement at the hub interface the MTBF is increased due to the lowered rate of fatigue. The fatigue rate is primarily dependant upon the angular displacement and not the tensile force or variation in thereof. Relatively the momentary overloading is a waste of time compared to specifically shaping the spoke correctly. I believe what you're concerned about is what Jobst Brandt describes as "improving the spoke line". The difference being that his concern is bends (loaded) at the flange and nipple, while you worry about the crossing. The concept seems the same, only the forces seem larger in the misalignments he describes. I am concerned about the movement of the spokes during the wheel's cyclic rotation and associated variance in spoke loading leading to that movement. I am also concerned about the lateral stability of the rim. The failure point is not the source of the problem. The fatigue failure of spokes at the hub interface will generally be due to not pre-forming the spoke at its crossing with the result that the crossing point moves in and out with cyclic load variance, and also torque applied to the rear wheel, bending the spoke at its contact point with the hub. Same as snapping a paper clip, bend it back and forth many times and it breaks. On wheels with spokes not shaped at the crossing point. If you take a straight edge to your 32x3 or what have you, lay it upon a spoke and slacken off a nipple, you will clearly see the spoke bend into the path of least resistance. Not a nice clean straight line required of a tensile component but loopy. When tight, the forces still remain, as each spoke in a pair fights against its brother. The tighter spoke will push harder and the not so tight will give because it is acting as a spring instead of a tensile member. If the spokes are pre-formed the spokes stop behaving as springs and the lateral stability of the wheel is much improved along with increased spoke life. TJ |
#69
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The Basics of Wheel Alignment and Wheelbuilding
Jose Rizal Wrote: Bending stresses do not result in only tension in cables or solid rods. One side will experience compression. You do not have this issue with spokes. ...Dodging again. Study some basic engineering. Fracture of a single strand in a cable decreases the load-bearing cross-section of the cable, which decreases the maximum load it can withstand. If the break happens because of a high enough load, the rest of the strands will experience higher stresses since there are less of them, and the cable will eventually fail. ...An absolutely ridiculous contention. A plane's skin is NOT a significant load bearing structure. The FRAME is. An airplane's skin is riveted for ease of manufacture, assembly and replacement. It has nothing to do with "fracture containment". So to you a cable = spoke = airplane skin. These are erroneous comparisons. ... And so? The ends of elevator cables are not free; nor of any cables used in any load-bearing application. These are crimped/welded/looped together to prevent movement of the strands relative to each other. One of the reasons this is done is to ensure that the tensile load is shared equally amongst the strands. If you EVER get compression in a strand of wire rope (cable is for television), I want to be far away because something BAD is going to happen. Wire rope unwinds when you put it in compression. Wire rope has a lower elastic modulus than say a spoke. Someone needs to read up on Roebling et al. Its unlikely that failure of a single strand in a wire rope will cause any failure given the lower elastic modulus of wire rope. Yes, you can make it fail but the analogy here is not accurate. And yes, an airplanes skin IS an IMPORTANT part of the total structure. I learned this back when I was a kid building model sailplanes. The structure is WEAK until the covering (silkspan, fabric or any of the shrinkable Mylar films) is applied, shrunk and painted. When the wing is positively loaded, the tension in the top is partially relieved while that on the bottom surface increases. For ultra high performance aircraft, the first third or so of the wing is sheeted in balsa, obeechi or light ply because no covering is strong enough for the compression. Enough aircraft, I forgot more than you know now. Wire ropes are ALWAYS wound with tension to ensure the inner strands do not go into compression. Since the wire is helical, the stresses are normalized except for the CORE which is usually INDEPENDENT as in Independent Wire Rope Core (IWRC). -- Weisse Luft |
#70
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The Basics of Wheel Alignment and Wheelbuilding
One spoke without pre-tensioning is more than adequate to support my static
weight Dynamic loads If the wheel is built to cope with a load of 7/5(rider + bike + luggage) this will be found to be adequate on a road bike. The capability of the wheel is simply tested with a weight equivalent to the calculated maximum force. The calculation is based on maximum wheel load attained on a front wheel during braking assuming a co-efficient of friction of almost 1 on a flat road(use of trigonometry). Maximum braking in a bend with positive banking may see this force may exceeded. I do not know whether the same test figure could be used for a track sprinter, but expect it to be not far off. Tensioning a wheel with pre-formed spokes. There is some trial and error until a person becomes practised and therefore skilled and so knows the particular feel with the spoke key as when to stop. If the mechanic starts with the spokes just a little bit tighter than slack then adds 1 turn and tests by placing weight on axle with rim on floor and it is found to be loose add 1/2 turn to all nipples. The torque required to turn the nipples will quickly increase and be felt in the fingers. This is the time to make any truing up, winding in the odd, not so tight spokes, as necessary, which will be found much easier than with spokes not pre-formed. Test again, add 1/4 turn if necessary. When suitably tensioned it should be found that all nipple movements will have an effect on rim position. Stiff , heavy rims may make this difficult to see without some form of indicator. The mechanic, after satisfying himself than all spokes are working equally, judged by equal rim movement with nipple turn, and that the rim will support the riders weight without reduction in lateral stability, judged by attempting to wiggle the bottom nipple in the spoke hole, can allow the rider to take a test ride. If the rider returns and says the wheel was wobbly, add 1/4 turn to all nipples and true up. try again or add load, ask rider to ride harder. If at any time the rider feels a wobble it is simple to add 1/4 turn and true up. A skill is something learnt with practice, and lots of testing and re-testing will be eliminated with experience of the method. Familiarity with the components using will also help to cut down the number of steps and uncertainty which accompanies any new method and associated skill. The use of the dynamic load calculation with static test would be the preferred method for a professional wheelbuilder. The likelihood of a wheel buckling that will lock up in the frame is greatly reduced with my preferred method of building a wheel, as the technique results in a wheel with a greater lateral stability and the lower compression levels in the rim allow a greater overhead available for dynamic load due to impact. Commonly available cheap steel spokes are required. It is unnecessary to seek out a particular brand or type. The load required to buckle my regular wheels would most probably bend the forks or frame first. TJ |
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