Solids and 3D printing
Why a shape does or does not print.
What "closed" means
A shape prints when every edge is shared by exactly two faces. Then there is a definite inside and a definite outside, and a slicer knows which part to fill. One missing face, or one edge with three faces on it, and it has to guess - and guesses come out as holes, blobs, or nothing at all.
Finding out
- Export STL. It says closed and ready to slice, or that a slicer will have to guess.
- If it is open,
/holesdraws every edge that nothing meets in red, over the model - so you can see where it is open rather than only that it is. It checks what you have selected, or every solid if nothing is. - Fix it and run
/holesagain. No red, and it is shut.
/holes draws every edge that nothing meets in red, so you can
see where the hole is - here, all around the opening the two missing
faces left.The usual causes
- A face missing. Draw the line that would close it and the face comes back - see the line tool.
- A face pointing the wrong way, drawn in the back-face color. Pick it and choose Reverse Face on the right button.
- Loose faces that never settled against their neighbors.
/rebuildworks the flat areas out again.
Where it lands on the bed
/center, or Center on the Origin on the right button - middles the selection across X and Y and stands it on Z zero. Where a slicer expects it./tozero, or Into the Corner at 0,0,0 - puts the near bottom corner there instead, so the thing stands on the floor with its edges against zero. What you want when you are measuring rather than printing.
STL and OpenSCAD exports do the centering for you, so there is nothing to move in the slicer.
See also
- Faces, front and back - which way a face points, and why the back is blue
- The eraser - how a face goes missing in the first place
- Exporting - STL, and what it says about the shape