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PostPosted: Thu Sep 01, 2011 6:10 pm 
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Built the wheel yet?


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PostPosted: Thu Sep 01, 2011 11:38 pm 
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No...I'm still trying to solve your spoke length equation :P (joke).

I've got to many things going on right now, so I will be building them over the winter.

I'll post pics when they're complete.


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Posted: Thu Sep 01, 2011 11:38 pm 


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PostPosted: Fri Sep 02, 2011 12:01 am 
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Lengths have already been solved for you. Nothing more to do other than plug the figures in. Just post the rim ERD, hub PCD, flange width and flange offset (distance of one of the flanges from the corresponding edge). I'll then get the calculator out and post the lengths for you here.
Even if you can measure the above to the nearest mm with a ruler, it should be sufficient.


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PostPosted: Wed Sep 07, 2011 1:21 am 
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Cryoplasm: Here are the measurements.

Rim ERD 586mm
Hub PCD 45mm DS & 44mm NDS
Flange width 53mm
Flange offset (center of hub to center of flange) 18.5mm DS & 34.5mm NDS

The spoke lengths I have calculated are as follows 283.68mm DS, 287.14 NDS cross, and 272.87mm NDS radial.
I'm interested to see what your calculations are. Also what would be the correct size spoke after factoring in stretch(sapim Cx-Ray NDS & DT Comps. DS)


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PostPosted: Wed Sep 07, 2011 2:02 pm 
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Thanks Brix.

Can't see how you found those figures out. The point of doing the calculation was because automatic calculator would not work.

I make the spoke lengths to be:

NDS, Crossed 287.51 mm
NDS, Radial 274.71 mm
DS, 305.97 mm (yes longer due to more extreme/obtuse bracing angle)

Regarding spoke stretch I suggest you contact DT and Sapim direct with the amount of tensile load you plan to use the spoke under.


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PostPosted: Wed Sep 07, 2011 4:25 pm 
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cryoplasm wrote:
Explain where you got those numbers from. You can calculate anything but with numbers pulled from thin air??


Calculate the difference in tension necessary between a crossed spoke and a radial one, to produce the same lateral force at the rim.


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PostPosted: Wed Sep 07, 2011 5:06 pm 
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rruff wrote:
cryoplasm wrote:
Explain where you got those numbers from. You can calculate anything but with numbers pulled from thin air??


Calculate the difference in tension necessary between a crossed spoke and a radial one, to produce the same lateral force at the rim.


Look you can't compare the two because the crossed spoke sits in different positions relative to a radial one. Yes there will be a difference but that's all you could say. If you plan to say more, give a specific reference to the crossed spoke. Further, you were giving some calculation of tension based on a spoke length of 280mm or something the other when you did not even know the spoke length or the spec of the wheel. It's called guessing.


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PostPosted: Wed Sep 07, 2011 9:31 pm 
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cryoplasm wrote:
Look you can't compare the two because the crossed spoke sits in different positions relative to a radial one. Yes there will be a difference but that's all you could say.


That's ridiculous... it is a simple geometry problem. I made the lateral offset the same, but you are welcome to vary it if you wish.

Quote:
It's called guessing.


It is called successfully refuting your statement that the variation in spoke tension was worth worrying about. For this, my "guesses" are plenty accurate. If you don't like them, then make up something else that is reasonable, and see if it supports your case.


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PostPosted: Wed Sep 07, 2011 10:38 pm 
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rruff wrote:
cryoplasm wrote:
Look you can't compare the two because the crossed spoke sits in different positions relative to a radial one. Yes there will be a difference but that's all you could say.


That's ridiculous... it is a simple geometry problem. I made the lateral offset the same, but you are welcome to vary it if you wish.


You lost me. It's ridiculous you're giving generalisation on spoke stretch and tensile load without knowing the properties of the spoke, nor the build spec. You can't pitch the set of spokes in question against each other and qualify the argument that way. Please go back to the beginning and explain this:

rruff wrote:
If you mean stretch, then yes... the long one will stretch 3 times as far... but you don't need to worry about that. As far as the wheel is concerned, the spoke is a force vector acting on the rim and the hub. So if all the parts are perfectly uniform, then the crossed spokes would have slightly higher tension. Compared to radial spoke with the same lateral offset, a tangentially crossed spoke on that hub would deviate ~280/(280mm^2-22.5mm^2)^.5 = 1.0032... the crossed spoke would have 0.3% higher tension. That is totally in the noise. Crossed spokes will vary more than that depending on which side they are on, and variations in the rim are at least 10 times greater (typically).


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PostPosted: Wed Sep 07, 2011 11:27 pm 
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cryoplasm wrote:
You lost me. It's ridiculous you're giving generalisation on spoke stretch and tensile load without knowing the properties of the spoke, nor the build spec.


Do you understand force vectors? If the lateral offset is the same, then compute the difference in the lateral force vector between a tangentially crossed spoke on a DA hub and a radial one. This will give the difference in tension... of ~0.3%. 22.5mm is the radius of the hub circle, and 280mm is the approximate spoke length for the rims he is considering.

The spoke specs don't matter at all.


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PostPosted: Thu Sep 08, 2011 12:18 am 
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rruff wrote:
Do you understand force vectors? If the lateral offset is the same, then compute the difference in the lateral force vector between a tangentially crossed spoke on a DA hub and a radial one. This will give the difference in tension... of ~0.3%. 22.5mm is the radius of the hub circle, and 280mm is the approximate spoke length for the rims he is considering.

The spoke specs don't matter at all.


The spoke spec does matter is determining their elongation under load.
I'm not sure why you're quoting the hub size or spoke size. These are almost irrelevant now that data has been refreshed in the discussion relevant to the actual wheel build. But even if you choose to present an example for argument sake you need to give two spoke lengths for a comparison.
Consider the deflection of the wheel at a spoke-rim interface point as the Moment around this point. At a radial juncture denote this Moment as Fx, and at crossed juncture call it F'x'. We know x' > x (from spoke lengths). Preserving Moments Fx = F'x' suggests F > F'. So you need greater lateral force to deflect the rim at a radial spoke than you would at a crossed spoke. However the story is still incomplete because the Moment at a crossed will be offset by the actual crossing. This lateral force is also independent of the tension in the spoke as the directions of action are orthogonal to one another. The tension in the spoke is transverse to the spoke and the system is held together with respect to the entire wheel.
You can not quantify the change in spoke tension as ~0.3% because no data here warrants such a claim.


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PostPosted: Thu Sep 08, 2011 6:09 am 
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cryoplasm wrote:
The spoke spec does matter is determining their elongation under load.


If you can find some reason to worry about elongation, when comparing the *tension* difference between a crossed and radial spoke, then let's have it.

Quote:
But even if you choose to present an example for argument sake you need to give two spoke lengths for a comparison.


Go ahead. Do you seriously believe that the length is going to matter? The spoke acts as a force vector along its length. If you know the tension, you know the force.

Quote:
Consider the deflection of the wheel at a spoke-rim interface point as the Moment around this point.


You are confusing yourself. This is about tension differences in a static wheel build, not deflection.


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PostPosted: Thu Sep 08, 2011 10:59 am 
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You are talking about Force, Tension and Lateral Force. You have them confused. Tension is one force in the spoke wrt the wheel. Deflection can be measured by Lateral Force, not Tension. I've already iterated this.

rruff wrote:
Do you understand force vectors? If the lateral offset is the same, then compute the difference in the lateral force vector between a tangentially crossed spoke on a DA hub and a radial one. This will give the difference in tension... of ~0.3%. 22.5mm is the radius of the hub circle, and 280mm is the approximate spoke length for the rims he is considering.

The spoke specs don't matter at all.


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PostPosted: Thu Sep 08, 2011 11:21 am 
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rruff wrote:
Go ahead. Do you seriously believe that the length is going to matter? The spoke acts as a force vector along its length. If you know the tension, you know the force.


You're the one doing some calculation involving spoke length.

rruff wrote:
If you mean stretch, then yes... the long one will stretch 3 times as far... but you don't need to worry about that. As far as the wheel is concerned, the spoke is a force vector acting on the rim and the hub. So if all the parts are perfectly uniform, then the crossed spokes would have slightly higher tension. Compared to radial spoke with the same lateral offset, a tangentially crossed spoke on that hub would deviate ~280/(280mm^2-22.5mm^2)^.5 = 1.0032... the crossed spoke would have 0.3% higher tension. That is totally in the noise. Crossed spokes will vary more than that depending on which side they are on, and variations in the rim are at least 10 times greater (typically).


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Posted: Thu Sep 08, 2011 11:21 am 


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PostPosted: Tue Jan 17, 2012 2:57 pm 
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Anyone have any updates on this? I've got a Planet X 20mm rim (24h) and a 36h White Industries eccentric ENO hub (36h) in my garage somewhere so i thought i'd see if i could have a go at a project to keep me interested over the winter.
Would love to know how Bricky got on with his design. My preference would probably be a 6 NDS, 18 DS with 2-cross just as it looks the simplest to build up but if the 12-12 design works well i might have a go at that.


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