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July 13, 2018 8 Comments
The goals of wheel building and racing are the same—speed and efficiency. I am not a fan of most side stressing schemes for wheelbuilders because I believe they add time but not quality. The intention is noble—to make wheels more stable by relieving pent up stress in the freshly assembled structure. This is often done with the wheel supported at the rim on a table and a piston applying side load to the hub or all spokes facing the piston. This isn't a cheap or compact tool. Granted, some of their users are very smart but...
...I contend there are better ways to accomplish stress relief/stabilization. The spoke path can be set by pressing spokes close to the hub (which can be accomplished numerous other ways). The side press does not create stress relief in the metallurgic sense, something steel spokes need. Builders of high end wheels, where batches are small can find better investments and processes.
Why do many builders not believe in side “stressing” tables. While tables are displayed on the Web, they are missing from many experienced build shops. I prefer methods with easily justified dynamics. Side stressing with hundreds of pounds of lateral force is nothing a wheel sees in service. The benefits can seem dubious (or at least indirect) to many.
From a metallurgy perspective, to enhance fatigue life tension must be be substantially, briefly, elevated. It is akin to heat treatment where a material enters a thermal zone that enables residual stress to escape.
Squeezing parallel spokes does this and has been justified by a many high end builders. Using gloves, the process will be the same. A tensiometer can simultaneously verify the magnitude of tension increase.
My research shows that one hard squeeze all around is enough. More may help in some cases but hard squeezes can cause minor untrueness. Don't become caught up feeling that more squeeze-true cycles is better. You're not wringing out a wet towel. The most important changes are microscopic and occur once.
When it comes to eliminating spoke windup, side loading can loosen spokes enough for twisted ones to unwind. However, the best strategy is banishing twist to begin with. This is done with a combination of thread lubrication, windup detection (via touch), and unwinding (reverse 1/8 turn after every adjustment). It’s always better to build spec into a process rather than QC-correct afterwards.
Trek/Bontrager has used tables that press on spokes 1/3 of the way from hub to rim. DT is similar. Don't push on the hub and pop the axle out! Theirs is a method for setting spoke angles, perhaps cost effective in volume situations. Set angles with steel rods (thick Philips screwdriver blades) or wood (retired hammer handles). If you do this aggressively once when the wheel is 80% tensioned, you’ll also be accomplishing the tension increase of squeezing. Your own tests will confirm.
Side stress tables may set spoke angles and release spoke windup but are NOT substitutes for stress relief. Stress relief is about optimizing fatigue resistance, not stability. Wheels that aren’t stable to begin with may show change with various loads. The goal is not to use tools to load wheels every which way but to create stable structures in the first place. That means no windup and brief, local tension increase once the wheel is finished.
Massive uniform side load is a load a wheel easily resists. Wheels can take gigantic side loads applied uniformly and it doesn't improve them. They can also take far more torque than freehubs but applying 300Nm torque during building would not make better rear wheels.
If you have money, space, time, and urge for a side stress table, go ahead. Prudent use should not harm wheels. Certainly, users of side stress tables are no fools. They have a strategy, but is it necessary for you? I contend you can skip the step and still build to the highest standard.
Avoid building steps that a) take time, and b) look like pre-use ritual. Correlation with actual engineering improvement must be proved and is often missing. Opt for speed, jettison anything that can’t be objectively justified, or repeatably measured.
Many of the most experienced and successful builders have tested and share this view. Of course, all ideas must continue to be challenged and views exchanged. Got valuable experience to share?
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