Hollow Sphere Design

Hello,

For my application I need to make some neutrally buoyant spheres. My idea is to make a hollow sphere since the printing material usually has specific gravity > 1. I'd like the OD to be around 0.4" and the ID to bring the specific gravity of the entire object - including hollow core - down to 1 (roughly 0.2" ID for specific gravities of the printing materials that I've found online).

My question is how to construct such a sphere using 3D printing. Most of the advice that I've found online goes the way of making two hemispheres but I'd like to avoid that if possible. Can one choose to have support material for the outside of the object so it doesn't roll during printing but not on the inside so that it is completely hollow inside? If it is hollow, can the object support extreme slopes (ie when printing near the top of the inside of the sphere). I'm a total newb in this world so any help would be much appreciated.

I'm sure these requirements will depend upon the printer and its printing method and materials. If you have some advice as to which printer might work best let me know. I do have access to the following printers here in San Diego (https://www.sandiego.gov/public-libr...nting-scanning) but I don't mind spending money if I need to either.

Thanks!
Nick

Hi, I recommend using a 25% inner support. Then you know the exact volume of the support and you can calculate the thickness of the shell using simple volume formulas. If it is too heavy, simply file some material off :) You will need a bit of trial and error if you want it to be very exact, unless you take into account all extrusion parameters, for example measuring the filament diameter at multiple places. Any FFF type 3D printer will do, make sure to print thin layers for a better waterproofing.