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Make your own polymer (UHMWPE) spokes?

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#681 ·
AdamR83 said:
Bad news for me, none of the alternatives come in yellow :cry::LOL: so I've gone ahead and rebuilt the roadie wheel with Stat20 XG. The used spoke ends could be successfully removed with the help of a heat gun, then cleaned up with the drill / sandpaper method.
Click to expand...
Sharpie markers stick pretty well, better than the dyes on some of the lines I've bought
 
#682 ·
It's a bummer the 1.5mm Marlow doesn't meet the standard, it was easily obtainable in the US. The 1.7mm Robline Maui is aggressively NOT available in the US. I can ship it to Afghanistan though, so there is that.

A non-compete is probably in place, have to figure out what brand/label is reselling it in these parts, if it proves to meet the quality standard.
 
#683 · (Edited)
I think the Marlow is just a bit inconsistent, or I got unlucky, or both. The test bit I bought was fine, and another chap has built wheels from it, so it could be worth a punt.

Braidtech might be an alternative though, I know they do a 1.7mm SK99 line with 500kg load capacity - exactly the same spec as the Robline, so may well be made for them by Teufelberger.

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I'm still wavering about whether I consider DM20 to be "essential" or not. I've had good results with it, but I think the SK99 wheels built at the end of 2021 have been ok because the static tension (I'd guess at less than 60kg) is so low relative to the breaking load of the line (over 600kg), therefore they haven't undergone any detectable creep. Either way, its worked.
 
#684 ·
Adam, do you pre stretch the spokes before lacing?

How do you calculate the spoke lengths? I was wondering how much the hitch and stretch factors into the calculation. Also would it be possible to use steel spoke lengths as a starting point and add a certain amount of millimeters to get the desired length for a finished wheel?

The hitch method is really elegant and does away with splices and thus potential slip points but getting the length correct seems somewhat difficult.
 
#685 · (Edited)
@Rakor , I build in a jig (pics on last page) which holds the hub in the centre of the rim. No need to calculate spoke lengths, I just make them in situ.

If you did want to pre-make them, it would be possible, if you know exactly how much cord is used for the hitch and how much stretch the spokes have (data in tables I posted a few pages back). Though making in situ in the jig has proven the easiest, most accurate and most repeatable method for me - previously I'd been making them to a calculated length.

I haven't pre stretched to date, as the amount of thread in a nipple is sufficient when you make the spokes exactly to size in the jig, but I'm considering it in future. The plan would be to set up a long piece, enough to do one half of a wheel entirely (say 5m), spliced loop at each end, attached to something solid at both ends (perhaps a couple of trees, ha) with a ratchet strap and my crane scale in there somewhere, then load it up to whatever value (maybe 150kg).
 
#686 ·
@AdamR83 Probably for the best you stopped faffing around with kite lines and Dyneema that’s prone to creep leave that wheel in a hot car and it’ll likely be a hot mess. What spoke tension are you running?

@SnowyNW I called up a marine supply store nearby that distributes robline. Request that they custom order you a roll of robline oceanstat20 2.0mm takes about a month

It’s a goofy size that isn’t really useful for anything beyond bicycle spokes. It’s mildly weaker than standard sk- series line. So often not as desirable for things like kitelines etc. and will need to be custom ordered. 1 roll did 6 wheels + a ton of screwing around for me
 
#690 · (Edited)
;) I think that's what Mike meant by custom graphics. I think the previous page has all the specs.

Got samples through yesterday, will test them today. The Robline Maui looks decent.

I think I'm around 50-60kg tension on the latest wheels, though one of my MTB rear wheels is way lower than this, maybe even as low as 20kg. Its so low that if you put all your weight on the saddle, some of the rear wheel spokes come completely loose! It's done hundreds of miles like that (including 4th place at our singlespeed UK champs, some trials, a bit of jumping) with no issues. I figure the line has 3x the stretch of a steel spoke, so you don't need anywhere near as much static tension.
 
#692 ·
I'll take that as a compliment shirk
Means I made it look pro :)

I make a lot of things, clothes, composites and now wheels. and generally feel products look better with sick graphics/logos. So I've made some logos I like and put them on my hand made products.

Armored carbon came from some composites work I did combining dyneema cloth for damage and impact resistance with carbon fiber for structural purposes. In the case of these wheels they are using the same materials Dyneema (also used as body armor) and carbon.

@AdamR83
60kg tension explains why you aren't getting into the pre-stretching screwballery I'm contantly struggling with.
I can hit 60-80 without using up too much spoke thread
but I'm insisting on 100-120kg which has been the biggest challenge for me...hopefully the strenchinator 3000 can solve this to a 1 and done point.

I know wheels can be ridden and ridden quite hard with little to no spoke tension. It is then relying more heavily on rim stiffness almost to prevent the wheel from lateral buckling. As Under impact it will have a span of spokes at zero tension.

Wider deeper, and stiffer rims will handle this better.

To take advantage of the flexible spokes, the rims I'm choosing are intentionally shallow and flexible. Just messing with them they feel relatively noodly and compress easily until spokes are added.

I have measured the rim. it will outflex the spokes by a considerable margin under the same load.
So I feel keeping the spokes tight and the noodly rim supported by the spokes is really important. Or it's likely to F off in a buckling direction.

From a lateral buckling perspecting (the weakest failure mode)
More spoke tension is better.
Stiffer rim is better
more spoke flexibility is better.
Anecdotally 3 out of 4 of my recent rim failures have come after checking (wire) spokes for wiggle and thinking "I should tighten those up".....and then heading out for a ride anyway or forgetting to tighten them after.

Sure less tension is fine. Berd says they target 80kg
F that. I've got stronger spokes... I'm gunna go at least as high as I would on a wire wheel to conserve overall buckling strength. Being more flexible they are less likley to create localized spike loads and want to rip out on impact.

The reason for wanting a noodly rim is so that it can flex and bounce over the rocks. The flexible spokes and rim system will flex more taking impacts better
 
#693 · (Edited)
Agree with most of that Mike, but can't figure out why more spoke tension is better for resisting lateral buckling. This is the way I see it - interested to hear your thought process too (y)

Since spokes (made from any of the materials discussed in this thread) obey Hooke's law, the load required (and displacement produced) to increase one from - say - 40kg to 70kg of tension, is the same as it takes to move it from 90kg to 120kg.

(A note on the UHMWPE spokes - they don't have a perfectly flat load vs extension curve, so you need to get past a certain loading point before they exhibit direct proportionality. The graph below is one from my testing, with the red line as the first load, the blue line the second. Seems that, when built into a wheel, it needs to be at 40-50kg tension before showing a straight line. I guess this is due to the fibres 'bedding down' into each other.)
Image



Thinking about a lateral load condition; given that the side of the wheel which experiences the force is the one that sees increased spoke tension (rim trying to move 'away' from the hub flange), with the other side reducing tension, could super low tensions perhaps give the opposite effect to what we expect? If the unloaded side still has some tension at the point of impact, those spokes are pulling the rim in the direction of the impact. If the spokes drop to zero tension, they aren't.

Radial loading would be different again, as you hinted, with rim stiffness being key (I also use shallow rims for this reason). The spoke tension / stiffness can make a difference here though, if you've seen the Berd testing vids then it shows spoke tension increases a couple of spokes 'around' from where the load is applied.


In 20+years of building at least couple of wheels a week, I've picked up the following generalisations:

  • Too high a tension kills rims, and occasionally hub flanges
  • Too low a tension causes steel spokes to break at the elbow (fatigue / work hardening)

And now maybe to add to that, if you have a spoke material which doesn't suffer from fatigue and work hardening, all the rules are re-written! :ROFLMAO:



Some more info that may be useful... having tested the samples I got from Ropelocker yesterday, the Robline feels and behaves like a much better product than Marlow of the same spec. It's about 25% more expensive so you'd expect this.

Graph for Robline 2mm (measures 1.8mm) DM20 vs 1.5mm (measures 1.6mm) Maui line:

Image


Basically it shows that the Maui before any bedding / stretching is virtually the same stiffness as bedded in / pre-stretched DM20, and that the post-production process on the Maui leaves it far closer to its eventual 'in use' state.

Given the above numbers, at 60kg tension a Maui spoke stretches about 2.5mm less than a DM20 one from first build to completed wheel (4mm vs 6.5mm). This is around 1% of the spoke length. Given that SK99 experiences about 1% creep per year at 20% load capacity, and 60kg tension is closer to 12%, that means it'll take close to 2 years for a Maui spoke to reach the same length as a DM20 one (had both been built at the same length). With the jig system I use for lacing the wheel and the extra long nipples, spoke length control / repeatability and nipple 'headroom' are both very favourable. So, I bought some more crappy kiteline ;) to build road wheels for a friend, and also to re-lace my XC race wheels.

I have the same data for all the other lines I mentioned a couple of pages back if anyone wants to see similar plots to help with their selection.
 
#694 ·
If any want different colours without the hassle of dying stuff, Paracord 550 has seven strings inside which can be removed easily leaving a hollow coloured tube that could be threaded over the spoke cord. I made custom footballs and used the hollow part of paracord for the bladder lacing when people wanted the laces to match in with designs I did. When it’s waxed it’s also pretty hard wearing and slip proof.

I also have a little manual machine that makes braided cord, it’s a mini version of how braided cord is actually done. I’ll post a pic of it when I’m back home. I’ve had it quite awhile so can’t remember if it was a kickstarter thing or through a leatherworker’s site, I know it wasn’t mass produced. Someone with bit more knowledge on gearing could probably adapt it to do spoke cord.
 
#695 · (Edited)
AdamR83 said:
Thinking about a lateral load condition;
Click to expand...
it's not a lateral load condition that induces the buckling it's (mostly) vertical loading...once the vertical load exceeds a certain point the structure is unstable and all that is needed is a hair of lateral loading and it'll venture off in the lateral direction .

this occurs because on a tall skinny structure that is loaded vertically the slightest flex in the lateral direction will create a small lever arm for the vertical load. Whichbends the structure sideways. (laterally) if it is not stiff enough it moves laterally thus increasing the lever arm the vertical force is using to bend the structure creating a postiive feedback loop until the whole thing fails.

Image

Push down on a vertical playing card you can see and feel this effect.

a bicycle rim on it's own is a pretty tall and skinny structure. So is inherently prone to buckling.
Looking at bicycle wheel when supported by spoke tension it looks like this with the spokes (skinny bits) stabilizing the rim laterally

Image

The spokes provide the structure which resists buckling making a stable structure
This is a WAY more stable shape against buckling than the rim on it's own

as the wheel gets a heavy vertical loading the spoke tensions will do this. (exagerated)
Image



so from a buckling perspective the shape of a rim will look something like this with the lower part of the wheel now unsupported in the lateral direction from about 45 degrees down as the lower spokes have no tension and don't contribute to support. The severity of this will depend on the loads applied but worst case high load or super low spoke tension looks as follows.
Image


Given the achievable impact angles on a bike wheel, in real life the dominant load will be vertical with a smaller lateral component. if you lose spoke tension the wheel becomes unsupported making the shape less stable and more likely to be pushed past a point of buckling instability. One way to reduce the amount unsupported structure is with more spoke tension. It will require more deformation before the spokes achieve zero tension. The other way is more flexible spokes. Add both and you've got a really great wheel.... :) that is ALSO less prone to spoke pull out.

for further reading I attached a pdf on buckling in the bicycle wheel that explains this in all it's non-linear confusion. Running through the equations you can find that spoke tension spoke flexibility and rim stiffness improve the critical buckling load

As you mentioned there is an ultrahigh tension beyond which the wheel simply is unstable under it's own load and prone to exploding. While fatigue cycling will generally become worse with higher tension as there is a larger range to cycle through.

In my opinion I believe it is very easy to obtain very low spoke tension in normal mountain biking....this is the most rational reason why my spokes tend to loosen over time....metal doesn't creep and when tight there isn't a lot of mass to make the nipples want to overcome the turning force from simple vibration... J bend spokes can't really turn. However if the spoke became loose temporarily . it is reasonable that the nipples may rattle around under the vibration which would tend to propagate in the loosening direction.. Which explains one of the reasons the good nipples have some locking thread aspect to them.

Looking at a huck to flat the amount of force required to nearly rim out a tire at 35 psi would be pretty severe. I'm making a hypothesis that if you were to load up a wheel like that you'd find at least a few spokes at low to no tension even if starting from high tension.

Image


So since I am convinced zero tension is reasonably achievable. Keeping a high spoke tension (within the rim makers limits) is an important design criteria for me given I'm not using a terribly stiff rim.
 

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#696 ·
Cemoz said:
If any want different colours without the hassle of dying stuff, Paracord 550 has seven strings inside which can be removed easily leaving a hollow coloured tube that could be threaded over the spoke cord. I
Click to expand...
there is a smaller paracord (330?) that works better for this as it fits over the line size we are using better.
It also protects against chafe very well. So someone may find some use on spokes there.

I use this on my kitesurfing lines at the attachment point to prevent wear. it's been on the back up plan for the spokes if I have long term wear issues at the hubs. Unsure if it'll fit through however.

I wouldn't add it to my spokes for cosmetic purposes as it just adds weight. Fabric paint, dyes and a pack of multicoloured sharpie's can achieve the same effect.
 
#698 ·
Here’s pics of little cord making machine, it should have a handle to wind it on the front spacer. I must of forgot to put it back in it’s storage box when I moved as it wasn’t in there with it. The thread on it isn’t particularly great so the long cord in pics is just plaited, if people are interested I’ll try to get it working properly. It works on sixteen strings, I believe the people who made it were going to make other string counts, I don’t think they did get around to it though.

It’s a little hard to see in the pic, there are 4 different sized holes on the top bar to make different thicknesses of cord.

Image

Image

Image
 
#699 · (Edited)
For any engineering types that want to dork out on bike wheels. Consider the following link.
bicyclewheel.info

bicyclewheel.info

bicyclewheel.info
bicyclewheel.info

there's 2 really solid links there

1) his PHd thesis on bicycle wheel optimization
Easily the single most complete analysis of modern bicycle wheel properties......Good modern theory backed and proven with testing.

2) How to characterize rim stiffness using acoustical methods....proven out and backed by testing. So you could in theory, sus out your wheel performance pretty accurately using a stick and a smart phone.

This is one of the few analysis that has actually addressed buckling (wheel failure) .
He was the author of the other paper I published earlier.

it's an engineering heavy read but well written.
I'm still going though it and will summarize my findings that are relevant to rope spokes, rim and tension selection and If I've changed my mind on whether it's a fundamentally good or bad idea to be smashing down hill at speed on these things.
 
#700 ·
Here's what I learned.
1. Flexible spokes are still a good idea.

2. High spoke tension is still a good idea (from a buckling strength perspective...up until a point...defined as roughly 1/2 o of the critical tension.
  • The critical tension is the tension at which the rim will complete buckle under an even spoke load. The critical tension is dictated by the rims radial lateral and torsional stiffness as well as some spoke properties.
  • at about 1/2 the critical tension internal pull is so hard that individual spokes begin buckling at the slightes out of true scenerio. but the overall hoop is still stable. This is Jobst Brandt's tighten till it goes wonky and back off 1/2 a turn guideline. This is mechanically the ideal tension.
  • For a modern double wall mountain bike wheel 0.5Tc is not realistically achievable with 2.0mm spokes and nipples. narrow single wall rims or road rims it may be achievable.
  • Increased spoke tension results in DECREASE in lateral stiffness. But overall increase in buckling resistance until 0.5Tc So if the goal is "lateral stiffness" a lower tension may be preferable.

3. Fat bike rims with postive spoke offsets is a good idea.
Single wall fat bike rims are a bad idea (weak in torsion)
Negative offset fatbike rims are a bad idea.
(i'm building a fatbike wheel so this was nice affirmation of my intuitive choices...however I may have selected deeper cross section to improve torsion)

4. The accuracy of mechanical properties from acoustic resonance is mind blowing. However I wouldn't expect it to translate to carbon fiber because the material is not Isotropic (same properties in each direction) So may have limtited value for high end wheels.
 
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