
Some shapes don't print well as designed. You've just got too many things like gravity and warping working against you, making it hard to get a nice smooth finish on the print.
Any object that has a steeply curved surface on the underside of the object is just about impossible to print without support, and even then, the surface has a lot of pitting, sagging and curling with some filaments. For these it's better to cut the object and print it in parts, with the curved surfaces flipped to the top, and a flat base at the bottom of each part.
Perfect example - this little salt pig I designed a while back. (It looks like a very simple shape, and it is, but it's just about impossible to get a smooth surface on the area shown without cutting the design.)
Very easy to do that in S3D:
1. Duplicate the model. (Edit > Duplicate Models > 1)
2. Select the copy and rotate it 180° around the X or Y axis. (Double click on the copy to pull up the menu.)
3. Raise the copy above the bed by X amount. However much you need to clear the curve. 15.0 mm in this case. (Double click the copy to select it and pull up the menu.)
4. Last step - select the original and sink it under the table by -X amount. (Double click on the original to select and pull up the menu.)
When you slice it, anything below the bed surface will not be printed, effectively cutting the object in half at the same place. (Even better, the curved surfaces are on top where they belong.) After printing, the two parts can be glued together.
That's it!
