3D Printing Explained

Learn more about model optimisation, segmentation, colouring and printing images.

For detailed explanations of 3D printing at the Fab Lab, please refer to the online video tutorials:


For a successful print, it's important that submitted prints follow the outlined requirements:

  • Minimum of 1mm thickness of all elements

  • 1:4 spanning ratio

  • Submission in the form of a closed geometry

Before submitting a print, read through all the necessary information for the selected printing type.

Scale and Details

Resizing geometry/models down to an appropriate scale is essential when preparing a 3D print model. Display models are rarely produced at a 1:1 scale, and different printers will have different boundary sizes to adhere to.

Not all digital models can be 3D printed

Due to digital constraints of geometry, or physical limitations of 3D printers, taking a digital model and simply scaling it down for 3D printing will not always work.


Understand what thicknesses are being digitally worked with by using a ruler when adapting a design for 3D printing.

E.g. Standard paper is 0.1mm, and is impossible to print successfully.

Adapt (or rebuild) a digital model

It will almost always be easier to rebuild a model for 3D printing. A properly adapted model can mean a higher quality return, and even save a lot of money in the long run.

Adapting a model could mean:

  • Simplification and/or reduction of design

  • Converting thin frames and/or columns to surface details

  • Elimination of elements

Note in the Above Image

Delicate balustrades eliminated, stairs and columns thickened, roof and wall details simplified.

Thickness to Span Ratio

In order to ensure weak points will be less susceptible to damage when getting handled during the post print processing phases, it's important to consider the thickness to span ratio.

Spanning beams and columns

For beams and similar long, thin structures maintain the 1:4 thickness to span ratio by inserting a supporting element at intersections.

E.g. 2mm thick beam will require a column at every 8mm length

Planar surfaces

For thin planar surfaces, consider including a ribbing designed into the underside.

Creating Closed Geometry

Geometry types

Models for 3D printing should only be composed of solids. In Rhino it's important to understand what type of geometry you are working with:



Point [1]

Represents a coordinate, a single location in space

Line [2]

Whether it is straight or curved, is best thought of as a collection of points. It traces a path through 3D space. A line cut in section creates a point.

Surface [3]

Surfaces have a front and a back, but no inside (thickness) so they cannot be 3D printed. Surfaces can be joined together to create a polysurface. A surface cut in section creates a line.

Solid [4]

A solid is geometry which has a volume. Multiple surfaces can be joined together to enclose a volume, which is then called a closed polysurface. If there is a hole in the surface or the surfaces do not completely enclose the volume, they do not make a solid. Closing these holes to form a solid is known as making the model watertight. A solid cut in section creates a surface.


In Rhino, geometry with a volume is known as a solid.

Surfaces cannot be 3D printed as they do not have a volume or thickness.

Objects which enclose a volume will have an inside and an outside. If you slice through a surface it will create a single line (Image 5). If you slice through a solid, it will create a closed profile (Image 6).

The easiest way to create solid models in Rhino is using the commands under the solid tools tab or the solid menu option.

Closed polysurfaces

In Rhino, joining surfaces together creates a polysurface, and if they completely enclose a volume, it creates a closed polysurface.

For the model to be 3D printable, the surfaces must be joined together into a single, closed polysurface (Image 8). To join surfaces, they must share an edge. If you are having trouble joining surfaces into a solid, it could be that some edges do not line up.

Did you Know? When you select an object in Rhino, the properties panel will tell you whether it is open or closed geometry.

Watertight models

“Watertight” is a common term used to describe closed or solid geometry. A watertight object has no holes, gaps or unjoined edges. Edges which are around an opening or not properly joined to another surface are called naked edges (Image 9). A watertight model has no naked edges. You can highlight naked edges in Rhino using the showedges > zoom command.

Connected solids

Ensure components within a model are joined before 3D printing. Components not joined together may come out as 2 separate pieces (Image 12).

Solid objects are combined using the BooleanUnion command. To boolean objects together, they must either overlap or have co-planar faces (Image 12). If the command does not work it is an indication that they may be slightly separated or not connected. In this case, move the objects closer to together and try again.

Did you Know? Use the intersect command to check whether objects are overlapping or sharing co-planar faces.

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