ARRK - General STL File Creation Advice

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General STL File Creation Advice

CAD Design

For StereoLithography it is essential that parts are complete and have continuity, i.e. the part to be built must be represented as closed surfaces that unambiguously define an enclosed volume.

A solid modeller defines a mass having an interior that is completely enclosed and is filled matter. Parts are always complete and have continuity when defined by a solid modeller.

A surface modeller builds a number of mathematical patches or surfaces that, when joined together, form the desired part. Because there is no defined association between these surfaces, it is possible to have gaps, discontinuances or even completely missing surfaces. To use a surface modeller for StereoLithography, the model must be 'fully surfaced', i.e. it must have a closed surface that completely defines an enclosed volume and the inside, outside and boundary of the part must be specified.

Bad STL
Section of an STL file showing a bad part with overlapping surfaces

Good STL
Section of an STL file showing a good part with one integral surface

STL Resolution

When creating an STL file from CAD, the resolution (also known as Tolerance, Chord Height or Facet Deviation) can be specified. Under-faceted STL files will affect the accuracy and may also affect the appearance of the SLA part. Over-faceted STL files will increase the time it takes to prepare the part, will not improve the quality of the final part, and may affect the delivery date.

There is therefore an optimum tolerance for the STL file to give the best accuracy possible, but not hinder work, due to very large files. From our experience the tolerance is best set between 0.008mm and 0.02mm and the overall file size should not normally be more than 10Mb binary.

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General STL File Creation Advice

CAD Design

STL Resolution