Spoke Madness, Chapter 2
Last post I shared images of exploded spokes. These were ridden off road and when the rim was damaged, the new rim required 2mm shorter spokes. These were shortened and threads re-run, a process done a zillion times a day across the planet.
Only, this time, the spokes blew up, would not accept a nipple. Here are close-ups of the ends. We’re in the middle of discovering what happened and images are part of the evidence. By the 3rd post (Chapter 3), we’ll be unravelling the cause and effect. By following along, I hope you’ll be better acquainted with spoke metallurgy, what to expect, and techniques to get the most from your wheels.
Here are two brand new spoke ends, same brand and gauge. No use whatever.
Unused but cracked? Are dents on each end (on exterior sides) clumsy wire cutting at factory?
These two ends are from ridden spokes. Since the use, no work has been done.
These look trimmed after factory anodizing. Material on each end is corrosion, tire sealant, thread compound?
These two used spokes were trimmed 2mm, but no threads run.
Used spokes, trimmed 2mm. The metal is unhappy. Is it too hard or deteriorated in some way?
Finally, three ends from used spokes that were both trimmed and rethreaded. Ghastly deformities, thankfully rare. Nearly no builder we’ve consulted has seen this so it makes a great puzzle to unravel.
Rolling threads over old threads (at the end) crumbles the metal like we’ve never before seen in a spoke.
By the next post, we need answers to at least these questions;
(1) Were new spokes too hard or brittle to begin? Did that predispose them to failure? Was the material defective ?
(2) Did riding cause work hardening or other deterioration? Was corrosion a factor?
(3) What are the relationships between hardness, strength, elasticity, and fatigue life in steel wire? What are the trade off’s between these? What best suits a spoke? What is contemporary spoke practice?
In order to answer these questions, samples will be metallurgically analyzed. We need to know stuff that doesn’t show in these dramatic images. I’ll share all the results except the spoke brand. No spoke maker should get kudo’s or demerits from such research. These samples are statistically insignificant.
Stay tuned and please contribute if you’ve been down this, or similar roads, before.
Did you ever follow up with a 3rd chapter post? If so I can’t find it.
Two post threads are unfinished. One you reference will feature microstructure and hardness images and tests to more fully explain this odd behavior. I expect to find machine adjustment is also a factor, but not solitary. The second unfinished thread is “bearings.” The last post will cover how hub bearings directly affect wheel building. These are getting delays but I’ll conclude in a month.
A very similar fracture pattern can be seen when baking cookies. Before cutting round cookies from a cylinder, I roll the dough to a sausage shape. The rolling needs to be interrupted quiet often to squeeze the dough radially and prevent a cracked core. Applying too much force while rolling guarantees the cracked core.
Could it be that the dies were too close together during rolling?
Bert, you got it! More on this subject soon.