COARSE FACETING

Coarse Faceting is almost always caused by an angle setting being too high, the deviation/chord height setting being too large, or a combination of both.

In the example, the hole has “flats” which almost resemble a stop sign. The resulting prototype will build a little small on the outer diameter, and a little small on the inner diameter, because the laser will cure the resin in the planes that are defined by the straight lines.

 

CORRECT FACETING

Correct Faceting is in between the two extremes. Quality faceting is just detailed enough so that features build to the file dimensions, while being simple enough to maintain a manageable file size.

In most cases, this can be obtained using .001” or .002” for deviation or chord height, and a modest angle setting.

WHAT ARE STL FILES?

The STL file is the industry standard for rapid prototyping and the format required to get instant on-line quotes. The STL file format is simply a mesh of triangles wrapped around a CAD model.

The size of the STL file is driven by two factors:
Complexity of the surface
Faceting options used to create the STL file

The more complex the surface, the more triangles produced. For example, if using simple geometry (not a lot of curves) the file may only be a couple hundred kilobytes. For complex models, 1 - 5MB file sizes will produce good parts.

The key faceting options are Chord Tolerance (deviation) and Angular Control (angle tolerance). These options will change the number of triangles and therefore the faceting or resolution on your STL file. The faceting or resolution will determine the relative coarseness or smoothness of a curved area. Additionally the more triangles placed on the surface of the model, the larger the STL file.

Faceting is controlled by the output settings of the CAD package being used. Below are examples of files with Coarse Faceting, Excessively Fine Faceting, and Correct Faceting.

 

STL FILE VERIFICATION

DPT’s on-line quoting tool will allow you to preview your STL file. Once the file is quoted, click on the viewer button to see a rendering of the STL file. If you have any questions please call a DPT project engineer. If your file is not optimum for build, a DPT project engineer will contact you.

 

CREATING STL FILES

GENERAL RULES

Always save STL files in binary format to reduce the file size
Some CAD systems will generate error messages during STL conversion showing that some part geometry is outside of the positive X, Y, Z quadrant or is in negative space. These warning messages can be ignored.

 

FROM SOLIDWORKS

  • Click on File > Save As. Select the path where you wish to save the file.
  • For File Type, use the drop-down arrow, choose .stl. Click Options.
  • Options - select Binary for file type.
  • Options - Total Quality: Choices are Coarse, Fine, and Custom. Choosing Custom allows access to Total Quality and Detail Quality sliders and fields.
  • In most cases, selecting Fine will produce an acceptable file. For custom, enter .001'' or .002'' for Deviation and 10 degrees for Angle Tolerance.

 

FROM PROENGINEER

  • Click on File > Save As.
  • Select the file type STL.
  • In the Export STL dialog box, set Format to Binary.
  • Set the Chord Height to .001”. The field will be replaced by a minimum acceptable value for the geometry of the model.
  • Set Angle Control to .5.
  • Name the file and click the OK button.
  • Pro/Engineer will save your STL file, and display your triangles on the screen.

 

FROM UNIGRAPHICS

  • Select File, Export, then Rapid Prototyping
  • Ensure it's binary. Set triangle to .001'' or .025mm.
  • Type in the file name, make sure the extension is .stl. Then select OK.
  • In class selection, select All, then OK.
  • Then discontinue, then OK.

 

FROM INVENTOR

  • Click on File > Save Copy As.
  • Select STL.
  • Choose Options > Set to High.
  • Enter File Name.
  • Save.