I purchased some painted foam eggs (“carveable”) that are about 6 inches long and 4 inches in diameter. We discovered that it is VERY useful to slow down the motors for plotting on larger objects, or the pen will bounce all over the place. We also discovered that some of our pen arm components were loose. Brian swapped out the faulty piece that holds the servo motor for the replacement that he requested for free along with the wider pen arm and diamond engraving tip that we purchased. These eggs are unfortunately pretty wonky in shape, so I’m having some pen contact issues, but otherwise things seem to be going more smoothly now that I’ve slowed it waaaayyy down (50 steps/sec). I think it was originally on 300 steps/sec, which works ok for chicken eggs. We also adjusted the current to the stepper motors following the wiki, but I think we probably ended with it approximately where it started.
I have some two piece plastic eggs and some ceramic eggs that are closer to chicken size to try next.