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How to make a SketchUp model solid for 3D printing

Updated · by Myles B

A SketchUp model prints well when each part is its own group or component that Entity Info calls a Solid Group or Solid Component. To get there, remove stray edges, internal faces and holes, flip reversed faces, then export with File › Export › 3D Model and choose STL.

What “solid” means in SketchUp

A solid is a group or component that encloses a closed volume with no leaks. Every edge must be shared by exactly two faces. Slicers need the same thing: a watertight shell they can fill.

Three things usually break it:

  • Holes. A missing face leaves an edge with only one face on it.
  • Extra geometry. A stray edge, or a face inside the shell (often left from drawing a part in place), puts zero or three faces on an edge.
  • Loose geometry. Faces that aren't inside a group or component can't be a solid at all.

Check whether a part is solid

  1. Select the part, and make it a group or component if it isn't one yet.
  2. Right-click it and choose Entity Info.
  3. Read the top line. Solid Group or Solid Component means it is watertight, and solids also show a volume. If it only says Group, something is leaking or there is extra geometry inside.

Check each part on its own. A group that holds other groups isn't a solid.

How to make a model watertight

Open the group (double-click it) and work through these:

  • Find holes. Orbit around and look for gaps. Redraw a missing face by tracing one of its edges with the Line tool.
  • Remove internal faces. Switch to View › Face Style › X-ray to see faces hidden inside the shell, then select and delete them.
  • Delete stray edges. Loose edges that border no face stop a part being solid. Zoom in on corners and the ends of lines. See stray edges.
  • Flip reversed faces. In View › Face Style › Monochrome, back faces show blue-grey. Right-click them and choose Reverse Faces. Slicers can misread a reversed face even on a solid part. See reversed faces.
  • Merge overlapping parts. If two solids overlap and should print as one, Tools › Outer Shell joins them and keeps only the outside faces.

Check Entity Info again after each fix. For models with many parts, the free Solid Inspector² extension can point you to the problem edges.

Watch the size and tiny details

STL files carry no units, and most slicers read the numbers as millimetres. Check Window › Model Info › Units before you export, and look at the part's size in the slicer before you print.

SketchUp merges points closer than about 0.001 inch, so very small details can lose faces and leave holes. A common fix is to model at 10 or 100 times the real size and scale down at export.

Thin parts need real thickness too. A single face, like a sign or a leaf, has no volume and gives the printer nothing to build.

Export the STL

  1. Choose File › Export › 3D Model.
  2. Pick STereolithography File (.stl) under Save As Type (Windows) or Format (macOS).
  3. Click Options. Tick Export Only Current Selection to save one part per file, and set the STL units to match your model.
  4. Click Export.

If the slicer still reports errors, go back to the part it names and check it in Entity Info.

How Lookover checks a model for printing

Lookover's built-in checks flag faces painted on the back side, leftover loose edges and zero-length edges, each with a one-click fix you can undo. For plain reversed faces, use Orient Faces as in the reversed faces guide. The print review also looks for reversed faces on closed parts. Lookover also reports edges shared by three or more faces, which stop a part being solid, so you can open the part and clean them up.

If you mention 3D printing when you start a review, or the model looks like a print, it adds print checks. They cover parts that aren't solid, parts with no thickness, size and units in millimetres, and walls too thin to print. Lookover tells you which objects to look at. It doesn't promise to make every part solid for you.

Questions

Why does my SketchUp model look fine but won't slice?

The shell probably leaks somewhere you can't see, such as a face inside it or a tiny gap at a corner. Check each part in Entity Info. If it doesn't say Solid Group or Solid Component, look for stray edges, inside faces and holes.

Should I export the whole model or one part at a time?

One part at a time if they print separately. Select the part, then tick Export Only Current Selection in the STL export options.

Why is my printed part tiny or huge?

STL files have no units, so the slicer assumes them, usually millimetres. Set the STL units in the export options to the unit you mean, and check the size in the slicer before printing.