One project I've been contemplating for some time is something to help balance shampoo bottles upside-down when they're near empty. The solution--a simple doughnut-like hollow cylinder--seemed like a good candidate:
The idea is that you rest the bottle atop the ceramic base most of the time and, when you eventually need to stand it upside-down, you invert it and place the lid in the central hole: I'm tentatively calling it 'Upside'.
The base modelling is fairly simple: drawing and extruding two concentric circles, then filleting the resulting edges. I parametrised the dimensions, so it's easier to adapt it to different bottles.
What makes things a little interesting is that tolerances for porcelain are large: Shapeways states, '± 3% shrinkage + 0.2-1.0 mm of glaze'. Since this particular design works if things are a little too big, but fails entirely if it's too small (and the lid of the bottle doesn't fit inside the central hole), I simply scaled the whole model by a factor of 1.03.
Overall things shrank a little more than I expected as I forgot to account for the glaze. Including this, it does indeed look like roughly 3% shrinkage:
- inner diameter, from 30.90 mm to 29.25 mm
- outer diameter, from 82.40 mm to 80.76 mm
- height, from 30.90 mm to 30.35 mm
Given the 3D printed nature of the design, I had expected it to be fairly precise. Instead, the print has a somewhat handmade, almost wabi-sabi look about it. That was disappointing at first, but I'm coming to like the result. The base is un-glazed, and has a fairly rough, abrasive texture, and might perhaps benefit from a piece of cork.