A very thin cylindrical ring is a lot like the center slice through a sphere, so the Eggbot can probably work okay on the surface, but I’m really not sure about the engraving part. The Eggbot is meant for drawing, and does not exert the kind of downforce that you would need to make a good mark with a handheld scribe-type engraving tool, and cannot support the weight of heavier, traditional engraving tools.
Two things that *might* work well, depending on budget and requirements: Our own diamond-point engraving tool– normally meant for hard surfaces like glass and stone –could actually be used to mark anodized aluminum, on a low vibration setting, with a slow travel speed. However, the marks will not be much finer than those that you get with an extra-fine point Sharpie marker. High-speed, lightweight engraving tools, such as the Turbo Carver could be used to good effect and make very fine lines, but cost a fair bit, and will take some work to mount to the Eggbot.
