Utah Engineers Journal 2021 Issue

63 Figure 1. Image of an STL File Ready for 3D Printing Figure 2. Civil 3D Expor t Sur face to Solid Dialog Box Figure 3. Sample STL File Depicting Solid Pipes and Drainage Structures The image below is an STL file created from a concrete water tank design consisting of a finished grade surface, a 3D model of the tank, and the associated tank and storm drain pipe networks. The creation of the Civil 3D objects that make up the design pictured above is beyond this article’s scope. However, the commands described below can convert Civil 3D objects into a single, 3D printable STL file. Export Surface to Solid. Entering EXPORTSURFACETOSOLID in the command line will bring up the following dialog: Select the TIN surface you want to export from the dropdown box. In the “Vertical definition” section, select “At a fixed elevation” and specify an elevation just below the minimum elevation of your selected surface. This selection will give your surface a thickness and a flat bottom at the elevation you specify, which is great for providing a solid first layer to your 3D print. Review the drawing output section, accept the default values or change as necessary for your needs. When you hit the Create Solid button, Civil 3D will create a solid model of your TIN surface. If your TIN surface is too dense (which is common when using LiDAR-derived terrain surfaces), you may need to use the SIMPLIFYSURFACE command to reduce the number of points in your TIN before you export the surface. Convert Pipe Network Elements to Solids In your design, you might have pipes or structures that are visible above ground that you want represented in your model, such as the maintenance holes, inlets and pipe and fitting shown in the image below: Civil 3D pressure and gravity pipe networks contain all the information needed to create 3D models of pipes and structures by default, but you need to use the CONVERTO3DSOLIDS command to create solid objects that you can export for 3D printing. If you start the command from a plan view orientation, you will get a warning recommending that you switch to a 3D view. If you get this warning, cancel, use ORBIT to rotate your view slightly and start the CONVERTOT3DSOLIDS command again. Now select the pipes and structures you want to export and hit enter. Choose whether you want to delete your existing pipes and structures (probably not, as this would break the annotation labels, styles, and profiles associated with those pipes and structures) and hit enter again. The result of this command should be individual “3D solid” objects representing your pipes and structures. Create Other 3D Solid Objects as Needed Civil 3D includes all the advanced 3D CAD commands necessary to create primitive 3D solids such as cubes, spheres, cylinders, cones, etc. You can use these commands to create basic representations of tanks, buildings and other features you might need to be included in your 3D print. For more complex 3D objects, research the EXTRUDE, LOFT, SWEEP, REVOLVE, and PRESSPULL commands. The large tank in Figure 1 was created by tracing a structural section view outline and using the REVOLVE command. Combine all 3D Solids and Export STL File Once you have all individual design elements converted to “3D solid” object types, use the UNION command Continued on the following page