@Ann: The article says that these are worm gears used for positioning of x-ray optics. I'm pretty sure the loads in this application will be relatively low, and the precision required is high (which rules out plastic gears). Also, I suspect that using lubrication in this application is a no-no - you don't want to have anything that could leak and contaminate your sample. For something like this, brass is ideal.
I agree with you that the article should have focused more on the gears themselves. I know a little bit about x-ray diffraction, since I am a materials guy, but I doubt very many other people reading this site are very interested in crystallography. Rather than focusing on the analytical capabilities of the diffractometer, the article should have focused on the design challenge which the gears needed to meet, and how Forest City Gear helped to meet that challenge.
Thanks, Dave. I should have qualified my comment by saying that brass gears don't work in load-bearing apps. I'm familiar with brass gears in clocks, although today it's hard to find a reasonably priced battery-powered clock with brass instead of plastic gears--how smart is that?
Anyway, my original question still stands: the article doesn't really tell us why brass gears are a good idea in this particular application.
@Ann: Your coffee grinder is a good illustration of the principle that what works well in one application doesn't necessarily work well in another application. Brass gears work well in applications with low loads and no lubricant where highly precise movement is needed. Clocks are a good example. Brass gears have been used in clocks for centuries. There are clocks with brass gears in the Milwaukee Art Museum which date from the 1500s and still work - so brass gears do last, at least in certain applications. Positioning optics for analytical instruments seems like another good application for brass gears. However, as you point out, a coffee grinder is probably not a good application.
I'm stuck on why brass gears are supposed to be such a great idea, vs steel or iron. Brass is too soft: gears made out of it don't last. I know this from personal experience with a handcrank coffee grinder. I still have the machine, and everything made out of wood and iron is just fine. But the brass gears gave out years ago and I haven't found steel replacements.
I often find it daunting that we have so far to go in research and development. Bruker is a solid company that makes some of the highest of high tech equipment. While the D8 Diffractometer incorporates vision-assisted automated sample positioning and detectors having a dynamic range limited only by theoretical calculations, they discovered the best step they could take to increase the utility of their instrument was to upgrade the quality of the mechanical gears. Even more humbling that the gears are made out of high-quality brass; an alloy we have been brewing since the height of the Roman Empire. Sometimes the way forward is to retrace our steps and revisit existing components. They were most likely optimized for an older version of "cutting edge."
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