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The .STL file format is the Rapid Prototyping industry's standard data transmission format. STL stands for stereolithography. STL files describe only the surface geometry of a three dimensional object without any representation of color, texture or other common CAD model attributes. This format approximates the surfaces of a solid model with triangles. These triangles share sides and vertices to form a mesh that forms the shell of a solid object. Almost all of today's CAD systems are capable of producing a .STL file. For the user the process is often as simple as selecting File, Save As, and .STL.
The relative coarseness or smoothness of a curved area is called a feature’s faceting. Faceting is controlled by the settings of the CAD package being used. The most common variables of faceting are chord height, deviation, and angle control/ tolerance. If the faceting is too coarse, any curved surface will not be rounded but rather it will almost resemble a stop sign. Coarse faceting is caused by the angle setting, deviation, or chord height being too large. On the other hand, the faceting can also be excessively fine. The shape will be very accurate but it will increase the size of the file. This is caused by the settings being too small. In between too coarse and too fine is good quality faceting where the shape of the object is not distorted but the file size is manageable. In most cases this can be obtained using .001” or .002” for deviation/ chord height, and a modest angle setting. To see if your .STL file is properly faceted it is a good idea to use the “Show STL Info Before File Saving” or “Preview” options if they are available in your CAD program. This way you can get a glimpse of the file quality.
Making .STL Files from SolidWorks 1. Click on <File><Save As>. Select the path where you wish to save the file. 2. For File Type, use the drop-down arrow, choose .STL. Click Options. 3. Options- select Binary for File Type. Binary files are approximately one fifth of the size of ASCII files. 4. Options- Total Quality: Choices are Course, 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 try entering .001” or .002” for Deviation and 10 degrees for Angle Tolerance. 5. Check the “Show STL Info Before File Saving” or “Preview” box to see a faceted view of the .STL file that you are creating. 6. Select “Done”, and send the file.
Making .STL Files from Pro/Engineer 1. Click on <File><Save a Copy>. 2. Select file type .STL. 3. In the Export STL dialog box, set Format to Binary. Binary files are approximately one fifth of the size of ASCII files. 4. Set Chord Height to .001”. The field will be replaced by a minimum acceptable value for the geometry of the model. 5. Set Angle Control to .5. 6. Name the file and click the OK button. Pro/Engineer will save your .STL file, and display your triangles on the screen.
Making .STL Files from Unigraphics 1. Select <File><Export>, then Rapid Prototyping. 2. Make sure that the file type is Binary. Set triangle to .001” or .025mm. 3. Type in the file name, make sure that the extension is .STL, then select OK. 4. In class section, select all, then OK. 5. Then discontinue, Then OK.
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