Autocad's various 3D modeling functions are straight-forward and easy to use, expecially if you're already familiar with the 2D interface and functionality. In the image shown here we have used Autocad 3D's Sweep function to creat a drive belt, and the pulley wheels were created using the Revolve function. Both operations require a drawn path and a profile.
In the case of the Sweep function, we select a 2D closed shape which represents the object's profile and project it along a similarly drawn path. This path may be open like a straight line, curved spline or helix; or it may be a closed path like a circle or closed polyline shape. The Sweep function is also useful for creating objects like threads or tubes on a mechanical fastener.
When drawing the path for the drive belt, we first go to the Top View and change the Visual Style to 2D Wireframe. We could then use the Polyline tool draw a horizontal line along the x-axis from the zero point and 220mm in length, for example. We could then enter a length of 175 at an angle of 135 to give us the second point. We then type C into the Command line to close the polyline shape.
This results in an equilateral triangle, as seen from above, the points of which will be the positions of the three wheel axles. Please note that it's best to use the Polyline tool in this context rather than the simpler Line tool. This will create a 3D object with less faces, meaning that it will render faster and use less memory. In this example each of the pulley wheels has a radius of 55mm, therefore we should use the 2D Offset tool to offset our triangle by 55. Next we should use the 2D Fillet tool to fillet each corner by a radius of 55mm. In this way, we see how an understanding of the 2D Autocad functionality is essential to working in the 3D interface.
The second part of the process is drawing the drive belt's cross-section profile. To do this we go to the Right View. In close proximity to the belt path we now draw a horizontal line 10mm in length, again with the Polyline tool. The next point is 10mm at an angle of 96, and the following top horizontal line is 5mm in length. Lastly we click on the initial point or type C and Enter to close the polyline shape. The last step is important or the corner will not fillet. This has resulted in a truncated box shape. We would now fillet each corner by 1mm radius as with the path shape.
The last step in the process is the easiest and is often done in an isometric view to see the three dimensions of the object. Then we simply select the Sweep tool from the top Ribbon tab (PC), and follow the instructions in the bottom Command line: we select the path, then we choose the profile, whereupon the 3D belt shape is created instantly.
We can see from this simple example that much of the 3D work starts initially in the 2D interface and functions. The 3D modeling aspect is an easy extension of those fundamental skills.
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.