johnbryanpeters
Well-Known Member
To an order of magnitude, one and a half thread diameters of engagement gives you as much strength as you're going to get.
Asymmetric Rims, did I get it right?
- Thread starter serviceguy
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serviceguy
Well-Known Member
Maybe I didn't understand what you meant, but I seriously doubt that would be the case. I'm also using alloy nipples.
johnbryanpeters
Well-Known Member
More plainly:
A half inch bolt screwed three quarters of an inch in is as strong as it's going to get.
The material doesn't matter.
A half inch bolt screwed three quarters of an inch in is as strong as it's going to get.
The material doesn't matter.
serviceguy
Well-Known Member
Ah, makes more sense that way. Even though I would expect the more the screw is in the larger the surface contact on the threads would spread the load.
Karate Monkey
Well-Known Member
@serviceguy you need to know how the calculator is rounding the calculus (@Patrick ). Specifically, how it is rounding the spoke length, and what the ERD field is actually asking for (spoke nipple seat, target spoke length, or somewhere in between). Without KNOWING those functions, you can't determine what the calculator is spitting out.
That said, if you're not sure, err on the side of longer, as long as the two answers are close. If the spoke threads are below the nipple slot (or head, in the case of squorx/whatever), you are going to break spoke nipples.
That said, if you're not sure, err on the side of longer, as long as the two answers are close. If the spoke threads are below the nipple slot (or head, in the case of squorx/whatever), you are going to break spoke nipples.
nope, not in reality, since the 'largest' thread takes the whole load until it deforms (slightly) then the next thread will start to take some of the load until it deforms, you get so many threads deformed and they can take the load between them without any issue. Theres a whole thread theory that applies to this stuff from the engineering side.
serviceguy
Well-Known Member
I was referring to the 'non rounded' spoke length results, on both calculators.
With regard to ERD this is what DTSwiss shows for it...
...and what Freespoke says about it...
Same difference? It gets tricky because I used Squorx in the DT Swiss calculator...never been a fan of flat screwdrivers.
The idea of slightly longer spokes seems to be supported by this article I've also found...
https://www.wheelfanatyk.com/blog/nipple-threads/
...and by largest you mean the first one that make contacts under load? What always fascinated me about threads is that you look at them as a succession of circles (I guess for ease of representation) instead of a continuous spiral.
I may have expressed myself incorrectly but that's what I was trying to describe, whatever little mechanical engineering notion I was exposed to were in a different language (ironically, I can almost exclusively talk tools in English though). To confirm what @johnbryanpeters was saying, the 'spreading' effect seems to became negligible once a number of threads are engaged? I guess it also depends by the machining precision of the fasteners involved.
Anyhow, wayyyy above the grade of complexity I was expecting...
The reason for my asking is that I've laced Ringle, DTSwiss and Stan's rims without any specific concern about spoke excessive length, I laced my last set of wheels using a WTB rim (KOM Tough) and the nipples barely cleared the inner rim profile (not a concern as WTB uses TPS, a tape strip that covers the nipple holes with the rim tape sitting on top of it), but having the threaded endof the spoke sticking out would make me a little nervous.
serviceguy
Well-Known Member
I never used that one, I find intersesting that in the list of hubs available they included each different color for a specific Hope hub...I’ll stick to DtSwiss or Freedpoke!
Karate Monkey
Well-Known Member
What you need to remember as a smoothbrain (myself included...): 5-6 threads of engagement=maximum strength. Spoke nipples are a bit strange, because they're shouldered sex-bolts, with a significant weakness in the shoulder...so there needs to be loading BEYOND that area. Note that internal nipples don't really suffer from this problem, because it's obvious if the spokes are too short--they just don't reach.
back-of-napkin calculations: average thread length for most spokes: 9.5mm. TPI: 56 (~2.2 threads/mm; spoke threading predates metric!). Thread length for a 12mm spoke nipple: ~7mm. You can thread a spoke on until you have about 2-2.5mm sticking out the top.
According to normal engineering practices, you could ASSUME that you might only need to thread the spoke nipple on ~3 turns...but you would be wrong. Both brass and aluminum lack the strength necessary to deal with the forces involved with carrying the expected load. If spoke nipples were made out of steel, the acceptable range would be (relatively) huge--but since they aren't, we need to make sure that more than the usual thread engagement is used.
The limiting factor on the strength would be the weakest material (yes the brass or al nipples), the thread theory still holds tho about the deformation, if you want to do the math I probably have the equations around I could look them up for you. (I get paid to do thus kind, of work for a living)
I'm not sure what you are trying to get at with the talk about a shouldered sex bolt, the spoke acts more like a wire and the hub hangs from the rim. You may have more thread available on a spoke than you would need with standa rd bolts, but they aren't adding any strength, just giving you room for the tension adjustment
I'm not sure what you are trying to get at with the talk about a shouldered sex bolt, the spoke acts more like a wire and the hub hangs from the rim. You may have more thread available on a spoke than you would need with standa rd bolts, but they aren't adding any strength, just giving you room for the tension adjustment
Karate Monkey
Well-Known Member
The bolt itself is acting as a part of the wire, and the shoulder/neck is rather fragile. It is unquestionably weaker than the wire. When spoke nipples break from fatigue, the head pops off. Under normal conditions, the spoke nipples don't break when the wire is through them (the nipples don't break from fatigue, the spoke heads do).
It might be tribalism, but it's around 60 collective years of experience.
The engineering conclusions of The Bicycle Wheel are beyond me, but good practices are not. Your can have the book if it interests you.
It might be tribalism, but it's around 60 collective years of experience.
The engineering conclusions of The Bicycle Wheel are beyond me, but good practices are not. Your can have the book if it interests you.
I believe most spokes are rolled threads, which means the thread-shoulder interface is a weak spot(no undercut for stress relief), however every spoke iv ever broken has been at the hub end not the nipple end.
The nipple should be plenty strong in this situation since it's only loaded axially and has a significantly more material than the spoke itself does.
I will see if o can get my hands on that book and have a look at what it's saying, it may be another 'best practices based on experience' type of guide book but should be interesting either way
P.s maybe we should let @serviceguy have his thread back 🤣
The nipple should be plenty strong in this situation since it's only loaded axially and has a significantly more material than the spoke itself does.
I will see if o can get my hands on that book and have a look at what it's saying, it may be another 'best practices based on experience' type of guide book but should be interesting either way
P.s maybe we should let @serviceguy have his thread back 🤣
this is interesting - it makes sense that it would break at the shoulder - the axial load creates torque any time the shoulder is side loaded by distortion of the rim.
work it back and forth enough and it is going to break. once the rim is out-of-round, it is multiplied. that being said, the fatigue breaks i've had have been at the 1 or two exposed threads at the nipple, and at the j-bend at the hub. i don't ride anywhere close to enough to have a good sample. and i break way more spokes by ingesting sticks or a derailleur.. all different weird forces going on - consider braking and accelerating, along with the hub "hanging"
work it back and forth enough and it is going to break. once the rim is out-of-round, it is multiplied. that being said, the fatigue breaks i've had have been at the 1 or two exposed threads at the nipple, and at the j-bend at the hub. i don't ride anywhere close to enough to have a good sample. and i break way more spokes by ingesting sticks or a derailleur.. all different weird forces going on - consider braking and accelerating, along with the hub "hanging"
Karate Monkey
Well-Known Member
It's not--Jobst Brandt was an engineer...also, quite opinionated, but again, not enough relevant experience to say one way or the other. I have a copy, just no idea where it is. If I can find it, I can media mail it to you.
@serviceguy just needs to remember that slightly too long > slightly too short
Karate Monkey
Well-Known Member
I've long ago let the ship sail that I'm not smart enough to understand WHY a wire spoke wheel works, but I am smart enough to build functional ones.
serviceguy
Well-Known Member
Not at all, I can't right now but I'm coming back and read the comments with more attention, I love getting into details and stuff...
Disappointing post, if anything for the lack of charts, spreadsheets and projections. You can do better than this.
I am smart enough to specifically avoid riding my bikes in order to prevent the inevitable failure that would prove how much I suck at building wheels. Do you want to buy any of my wheelsets?
The threads are weaker than the shoulder, (this is why when you have a 'pin' type connection made with a bolt in shear the shear area is ALWAYS on the shoulder of the bolt, think your trailer hitch in the receiver, if you put that together with a bolt the smooth shoulder would be where the pieces are sliding past each other), the weak spot is actually the transition between threads and shoulder(in tension of course, we already established that you dont design shear loads into the thread length). This is because the sharp edge concentrates the stresses and causes fracture. When you design a shoulder bolt for strength in tension you put a smooth/round undercut at the end of the threads/beginning of the shoulder, this basically guides the stress around the edge smoothly, significantly reducing the peak stresses in that area, making the bolt stronger. it seems counter-intuintive taking away material to make it stronger, but thats how it works.
Karate Monkey
Well-Known Member
I agree that threads are typically the weak point on a fastener--but remember that spoke threads are rolled onto the spoke. The material is literally being forged with threads, and transitions to a threaded area that is nominally .2mm larger than the wire stock. There's a zone on the end of the spoke threads that gradually tapers back to the wire size, if you look at it through a loupe. AFAIK, spoke nipple threads are cut, and aren't sophisticated--the area with flats/splines on the outside of the rim is unthreaded, and the rest go through. Most of the book I mentioned goes towards explaining common misconceptions of how the wheel works; a system of tensioned wires to hold the hub/rim in relation to each other. If the person doing their job building/engineering the wheel does it right, there should be next to no shear stress on the spokes (look at why we don't have radially spoked disc brake wheels [nb: they exist, and are still stupid]).
Depends how cheap. I've got lots of spokes
