After you created or imported a 3D model, some preparation is usually required to make it 3D printer friendly. This blog post describes some of the most important ones.

Translating

After important a model, it is often necessary to translate the model to the origin before working with it.  Take the Darth Vader model below for example, after importing it into Autodesk 123D Design, one will find that it is well above the ground plane.

To fix the problem using the translation and rotation feature and to viewing perspective cube at the top-right to bring Darth Vader down to the ground plane.

 Scaling

If you designed the model using the units that you actually wants to use, then this step may not be required.  If you import a model from an external source, often the model needs to be scaled to fit within the printer’s build volume, and your desired size.  Autodesk 123D Design can be used scale the volume.  The Darth Vador above is rather large, as is evident by the fact the ground plane, which has a millimeter grid, is so dense that it becomes a solid plane.   To scale Darth Vador down to size, use the scale tool:

Now, notice the scaling will introduce more offsets.  To remove the offset, simply use the translation tool to move the scaled model down more.  More often than not, the translation tool and the scaling tools need to be used iteratively to bring out the desired result.  After a few iterations, a 7.5cm wide Darth Vader model is achieved.  Now let’s make sure we save the model as a 123D Design file, but also export is as an STL file.

Water-Tight

Now that we have a good looking model at the right size, the model must be made into a solid before printing, otherwise it is just a group of surfaces, or mesh.  Often the design may appear to be a solid, but if there is any holes in the exterior surface, the model becomes a hollow shell with surfaces that have zero thickness.  3D printer usually cannot print such model.  To ensure the model you designed or imported does not have holes, the model must be made water-tight by the right tool.   A free tool that will check whether an STL file is water-tight is Netfabb Basic.  Autodesk 123D Design provides such support through the 3D Print button:

The button will bring up another Autodesk tool called Meshmixer, which will check and repair the model to ensure that it is water tight:

After the model is repaired, export the model as a STL file.  The Export button is at the bottom left of the Meshmixer window.

Careful comparison of the repair model and the original model, one will fine the repaired model is fully enclosed, and there is more smooth.  The repair model is now almost suitable for importing into the 3D printing software, such as Simplify3D.

Slicing

Sometimes a model is complex enough that it needs to be sliced into more 3D-printable pieces.  For example, the X-Wing Flighter when sliced like the figure below, will make it much easier to “extrude” or print.  Notice the plane where the slice occurs is where the maximum cross section area.

Adding Support

While slicing a model can improve 3D printing, it requires one glue the pieces together after printing.  Alternatively, one can add support to the model to enable help 3D printer.  Both Simply3D and Meshmixer supports adding support.  But I find Meshmixer produces better support structure that is easlier to break off after printing.  Below is an example of Darth Vader with support structure added.  After the support is added, the model with support can be exported as a STL file, which can then be imported by Simplfy3D.  In this case, the model should be printed without Simply3D adding any additional support.