Repairing 3D Files With Meshmixer and Netfabb

Sherri Johnson of CatzPaw offers repair advice for 3D models

Sherri Johnson of Catzpaw Innovations shares more advice on using Meshmixer and Netfabb to improve your 3D models so that they print better.

In the world of 3D printing, just because you create or download a STL file, does not mean it will print. Not all STL files are printable; even if they look good in the CAD file and the STL viewer. To be printable, a model must be:

  • Watertight - have no holes in the mesh; if you poured water into it, none would leak out.
  • Solid - the model must be one solid piece with no surface intersections.
  • Manifold - each edge must connect to exactly two faces [any more and there will be internal faces, any less and there will be holes].
  • Made from Front-Facing Polygons - the normals (fronts) must face out, cannot overlap or have overlapping vertices.

In addition, these issues can also cause a model not to print:

  • Intersecting or Overlapping Faces
  • Duplicate Faces
  • Group inside a group
  • Internal Faces
  • Reversed Faces
  • Stray Lines

Any of the conditions above mean that you want to open the STL file in a utility program that is capable of checking for issues and correcting those issues, either automatically or manually. Some slicing programs (such as Simplify3D) offer repair tools as do some of the CAD programs (SketchUp extensions). Dedicated applications, that are also free, which include the most repair tools are netFabb, and MeshMixer.

As an example, in the photo above, you see the Fire Fighter figure looks great in the STL viewer, but look at what happens when the model is analyzed for errors in MeshMixer. You start to see Red Pins which mean the area is "non-manifold" (see Manifold definition above) and Magenta Pins indicate small disconnected parts.

Meshmixer will also show Blue Pins to let you see where there are holes in the mesh. At least this model has no holes.

MeshMixer offers an auto-repair tool; however, the results may not be desirable; it likes to delete problem areas. That's far from ideal. In this case, Sherri explained that she used the " Hollow with wall thickness" repair tool to thicken the walls of the model, connect the disconnected parts, and make the model manifold. When the object is analyzed a second time, only four problem areas remained to be fixed.

Netfabb is another repair tool that has become the industry standard. There are three versions available: Pro, Single/Home User, and Basic. The basic version is free and can repair most errors. Depending upon the CAD software used and the number of repairs needed, one of the more robust versions of Netfabb may be needed. By using design applications geared towards the creation of models for 3D printing, such as 123D Design and TinkerCad, the number of repairs needed is minimal and can easily be handled by one of the free products.

The Fire Fighter, shown above, is used again as the test model to show Netfabb’s analysis and repair tools.

Netfabb’s analysis is much more detailed and allows for repairs to be manually on a per-polygon basis.

This can be very time consuming and in most cases, the Netfabb Default repair script can fix most issues with a model. When Netfabb exports a repaired file back to the STL format, it runs a second analysis of the object for any additional repairs that may be needed.

It is always a good idea to run any repair tool multiple times. Each time the analysis and repair process is run; more issues are found and fixed. Sometimes one repair can introduce another issue. Both of the mentioned tools have great tutorials and helpful information on their websites.

Sherri provided the links to her favorite tools:

Autodesk Meshmixer - http://www.123dapp.com/meshmixer

netfabb - http://www.netfabb.com

If you are looking for examples of how Sherri and Yolanda have solved real-world challenges with their own 3D printing business, then head to their Facebook page: Catzpaw Innovations.