[Note: this is #2 in a series of tips to be published during 2009.]
Lubricate your nipples. Yes, yes, you've heard this advice before...maybe back when you were a runner? Seriously, it sounds simple but deserves emphasis. Why does it matter and what is the science behind this practice? What are the practical benefits and what are some effective means to lube nipples?
It's worth asking, to begin the discussion, why this lubrication is not universal? Seems simple, why doesn't everyone already do it? There are actually several good reasons, besides inexperience, that some builders (especially mass producers) continue to build dry.
(1) Brass, the most common nipple material, has a self lubricating property and is remarkably smooth turning. This low coefficient of friction against steel and aluminum means you can almost skip lubrication in the threads.
(2) Corrosion resistance of brass is also quite good, which explains why it is used for so many nautical fittings. While not equivalent to stainless materials, this resistance makes lubrication less important.
(3) Nipples become cemented in place by the corrosion that eventually occurs with dry brass nipples, which helps stabilize a wheel against vibration induced loosening. Trouble turning nipples means difficult re-truing but freedom from loosening is a valuable benefit.
(4) A dry nipple reaches a point where no further turning is possible, the combination of thread and rim friction becomes too much. This acts as a handy signal to the builder to stop tightening and simply finish the wheel. No tension gauge needed. Conveniently for mass producers, the signal comes early at lower tension than conscientious builders prefer.
Well, none of those factors apply to us. We all seek high optimal tension for maximum wheel stiffness and longevity. Right?
Lubricating nipples should focus on the nipple to rim contact, not the threads. The former produces much more friction than the threads. Thread friction is, however, still important especially because it can cause a spoke to wind up. Wind up confuses the builder, masking the precise magnitudes of adjustments. It also stresses the spoke at the threads, a weakness best to avoid. Light oil is the best all around lubrication for these parts although I've heard builders use a grease stick on rims prior to building. I'm a big fan of pin point oilers. Here are a couple near my truing stand. These can be bought at many hardware stores. Find one you like and use it!
Many builders like coating spokes with a Teflon material like SpokePrep, that lubricates the threads and has other benefits. While I'm fond of the practice (having created SpokePrep some years back), I've become lazy in recent years. Supervising off shore wheel building always reminds me to avoid processes that are hard to teach and monitor. SpokePrep and other coatings don't work well in large wheel workshops. My conclusion is to lube threads early in a wheels assembly and, when finished, to use a wicking Loctite. I prefer 220 (blue, NOT 222) for this. But more on thread compounds later.