When modeling in the 3D environment of AutoCAD we can use many of the 2D functions as well as a combination of 3D commands to create our finished model. For example, in the case of the 3D sparkplug shown here, we could either create it from scratch using 3D functions, or, if we have a 2D drawing of the object, we can modify and extrude from this.
In the latter case we would open the 2D drawing and hide any unnecessary layers. We only need half of the drawing, so we would create a vertical centre line and delete one half of the drawing. Then resave the document. Next we switch to the 3D workspace using the Workspace Shifter button on the bottom right of the Status bar. This will open some 3D commands on the top Ribbon, adding to the already present 2D functions.
In terms of 3D modeling, the 3D sparkplug can be split into five main components, each of which requires a slightly different 3D modeling process. The terminal, ribs and insulator at the top of the sparkplug comprise one section. The hexagonal casing is the second part. The seals below this comprise another section. The threads are created using a different process. And the bottom ground electrode is the fifth part. Each of these five parts should be converted into a single Polyline. This is done by typing PE into the Command line at the bottom of the interface, then selecting the lines and arcs that make up the part, and choosing the Join command. This means that the polyline shape can be modified in one operation, and results in less geometry, which in turn keeps the file size down.
For the terminal ribs and insulator section we need to use the centre line as an axis of rotation. First select the Revolve command from the 3D operations tab at the top left of the Ribbon. Then select the polyline you wish to rotate in 3D space and hit Enter to finish the selection. AutoCAD then asks for two endpoints of a path which will act as a rotational axis. Lastly an angle of revolution is required. This is usually 360° for a full revolution, but you could also choose 180° for a half section.
The next section is the hexagonal casing which should be redrawn in the top or plan view. This can be achieved by double-clicking on the top of the View Cube on the top right of the interface. We choose the 2D Polygon tool and specify the number of sides, as well as the centre of the polygon, and the radius. In the case where the side length of the hexagon is known, use the Inscribed method of drawing the hex, since this will equal the radius. (The hexagon is, of course, made up of six equilateral triangles.) Using the Extrude command, the hexagon is then extruded downwards for its height, and moved into place, if necessary.
We return to the front view of the drawing to create the next section, being the seals. These are a simply revolve command like the one above, again using the centre line as the axis of revolution.
The threads we create using first the Helix tool, describing the number of turns and the height of each turn, or the overall height of the thread. Then we create the thread profile. The processing required to create a rectangular thread is too much for the program, so I would use a simply circular profile. Then use the Loft command to project the circle along the length of the helix.
Finally the lines making up the ground electrode are converted into a polyline and extruded backwards to add depth to the shape.
Materials and lighting may now be added to the sparkplug model, and the resulting model either exported to a still image or an animated video.
Tom Gillan has been training AutoCAD 3D to corporate clients in Sydney for seven years. If you like to know more about AutoCAD 3D, visit Design Workshop Sydney for more information.