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What to pay attention to when converting 3D models to STL files

As we all know, the STL format model needs to be prepared before 3D printing, but some modeling software will always encounter some small problems in the process of exporting the STL format. Therefore, we need to master some precautions of STL file format in advance, as well as possible defects in the process of STL file conversion, so that we can better solve the problem.

Note on STL model:

1. Common vertex rules

Each of the two adjacent triangular planes must and can only share two vertices. That is, the vertex of a triangular plane cannot fall on the edge of any adjacent small triangular plane.

2. Orientation rules

For each small triangular plane, the normal vector must be outward, the direction of the vector formed by the three vertices must be determined in counterclockwise order (the right-hand rule), and there must be no orientation contradiction for adjacent small triangular planes.

3. Value rules

The vertex coordinate values of each small triangular plane must be positive, and zero and negative values are wrong.

4. Full of rules

All the surfaces of the three-dimensional model must be covered with small triangular surfaces without any omissions.

Possible pitfalls of converting STL format:

Some unexpected defects may occur when the model built with CAD, PROE, and other modeling software is converted to STL format.

1. There is a gap, that is, the loss of the triangular surface

This error occurs when triangulating the intersecting parts of surfaces of large curvature. On the displayed STL format model, there will be wrong cracks or holes (no triangles in them), which violates the full rule.

At this time, several small triangular surfaces should be added along these cracks or holes to eliminate this error.

2. Distortion, that is, all sides of the triangular surface are collinear

This defect usually occurs in the conversion algorithms from 3D entities to STL files. Because the triangular surfaces are generated by different entities at their intersecting lines, the distortion of the triangular surfaces at the intersecting lines will be caused.

3. Overlap of triangular surfaces

The overlap of the surfaces is mainly caused by the numerical rounding error during the triangulation of the surfaces. Because the vertices of a triangle are represented in 3D space as floating-point numbers, not integers. If the rounding error range is large, it will lead to overlap of the surface.

4. Ambiguous topological relations

According to the common vertex rule, there are only two triangles with common sides on either side. If more than two triangles share this side, an ambiguous topological relationship is created. These problems can occur when errors occur in control parameters when triangulating planes with sharp corners, intersecting parts of different entities, or when generating STL files.

Due to this defect in the STL file, the validity of the STL model must be checked in advance to ensure the success of 3D printing. Otherwise, a defective STL file can cause many problems and even crash in severe cases.

The solution:

Because of the above defects and deficiencies of STL files, it is often necessary to use repair software to modify STL files. Compared with magics, netfabb, 3d build, etc., however, the automatic repair function of most software can only stay on correcting simple errors, and can not automatically repair complex errors, and some models still need to be manually repaired. What to pay attention to when converting 3D models to STL files


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