How to handle slicing tops/bottoms of spheres?

[sprior]

Sitting home with the flu today thinking about 3D printing...

In the past I've tried to create some thin wall items which are spherical - christmas ornaments, shades, and the problem is that when slicing the tops and bottoms of the spherical shape the layers shift so far from one another that they don't support each other. Even changing the layer thickness to 0.1mm isn't enough and that would slow the entire print down to a crawl.

What's the best way to handle these areas?

[ednisley]

the layers shift so far from one another that they don't support each other

Geometry definitely isn't on your side in a 3D printed sphere: you can't use a single perimeter thread, because the top layers will always be unsupported, no matter what thread thickness or width you use.

Some ideas:

Add internal supports under the center of the dome. The rule of thumb puts supports under an overhang tilted more than 45° from vertical, although that certainly depends on what you're building.

Add more perimeter threads: the inner ones will collapse as before, the next few will build on the rubble, and the outer threads should come out OK. That's no good for a sphere which must have a thin wall, but if you're building a textured ball, it might be acceptable.

Cut it in two and print the hemispheres upside down with supports under the central section. The nozzle motion tends to pull the thread inward, which will keep it from collapsing outward, so perhaps you can get away with less support than you might expect. You must glue the halves together and finish the exterior, of course.

Ain't nothing simple...

[Tim]

I haven't tried this, but it should be possible in S3D to define a different process for the topmost (and/or bottommost) layers, maybe both to decrease the layer height and also to set a large number of perimeter shells