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Centering technique

edited November 2013 in Egg-Bot
I have a difficult time centering objects to be printed in holders.

Any suggestions or a preferred technique for simplifying or speeding up this process and minimizing wobble?




  • What kinds of objects are you printing on?  And, are you printing one-after-another of the same type of thing, or always changing between different types of things?
  • I print almost entirely on "round" Christmas bulbs.  To be sure the object is centered, I place the Egg-Bot on top of a sheet of printer paper, then use a sharpie to place a small dot of ink on the page.  As I stand over the bot, I align the edge of the bulb, visually, with that small dot.  As I manually rotate the ornament I can see "wobble", and that tells me where and how far off my centering is.  I correct the placement, then check again.  When I can spin the bulb 360 deg. and not see much wobble I call it good and begin the plot.  It's a technique used on well over 100 bulbs and is often good for such  projects.  Video of last years ornaments is here: You can see my notebook paper under the Egg-Bot, but the alignment dot is just out of the shot on the bottom edge of the video.  My biggest hurdle was with the origional clear pads... they didn't work very well with the smooth glass.  A precision egg coupler solved most of those problems, and I highly recommend it if you don't already have one.  Trial and error works best, and I'm sure you will find something that works well for you.
  • Windell - I am printing glass Christmas balls.

    MLowe - Thanks for sharing your techniques, I will try them.  I do have the precision coupler.  I have also tried engraving with the engraving attachment but have experienced really high breakage.  Have you tried engraving?

    I also have a 3D printer, perhaps I can devise some sort of holder to position glass balls that can be printed.


  • Our technique is much like mlowe's, except that we just sight over the edge of the ornament to the edge of the Eggbot's frame.  With motors off and pen up, I spin the ornament around one full turn by hand, and align it such that the highest point is pointing up.  Then, push the ornament into the spring plunger just a little, slide the end down at the motor side, and spin it around again to check.  Usually, this takes just that two pairs of spins and about fifteen seconds, when switching between two objects of the same type.

    The precision egg coupler itself is *great* for eggs, but doesn't work well on bare glass surfaces.  There should be a big rubber washer that came with your kit, which serves as a grippy interface between the glass and the coupler.

    If you are experiencing breakage while engraving, there are a few things that you might consider:
    - Try to find some ornaments that have thicker walls. You can tell by tapping the surfaces.  Some ornaments are simply paper thin, and there's hardly anything you can do to avoid breaking them while engraving.  Ornaments with thicker walls can be much more robust.
    - Reduce the vibrating speed of the motor, move more slowly.  This makes marks that are less deep, but more accurate.
    - And the other big one: Reduce pressure.  Let the diamond tip barely touch the surface, rather than using the springy hinge to push it down.  
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