Calibration Sphere

We've all seen, and printed, the XYZ calibration cubes. Not only do they work great to test dimensional accuracy as well as z-wobble, ghosting and a host of other issues, but when printed in vase mode, they work great to purge filament in between color changes. However, I have found that some filament will print beautifully on the straight edges of the cube, but problems show up when printing rounded or curved surfaces.

To that end, I have made this simple, hollowed out, high resolution, 20m