Cad Concepts
Most products at Siliconrax have been defined using a combination of “Bottom-up & Top-down” design techniques defined below. In all cases, the components to be used in the product must be defined and accurate solid models of them (hard drives, motherboards, cards, LED’s, hardware, etc...) need to be created.
Often these components cannot be obtained as 3D solid models but have only 2d drawings with which to define them. These drawings may be “Vector graphic” (Autocad, Solidworks) or “Raster type” (bitmap, jpeg, PDF). The Raster drawings may be converted to Vector type graphics or used to create such with the use of software such as Corel Draw or Adobe Illustrator. Drawings are then imported to Solidworks to create solid models from orthographic and other views. Care must be taken in the use of this method of part definition as abnormal scaling can result from translation or originating from the source.
Vector - smooth edged because shapes are mathematically defined instead of mapped into individual pixels.
Raster - raster graphics use pixel-square approximation.
Bottom-up design is the traditional method. In bottom-up design, you create parts, insert them into an assembly, and mate them as required by your design. Bottom-up design is the preferred technique when you are using previously constructed, off-the-shelf parts.
An advantage of bottom-up design is that because components are designed independently, their relationships and regeneration behavior are simpler than in top-down design. Working bottom-up allows you to focus on the individual parts. It is a good method to use if you do not need to create references that control the size or shape of parts with respect to each other.
Top-down design is different because you start your work in the assembly. You can use the geometry of one part to help define other parts, or to create machined features that are added only after the parts are assembled. You can start with a layout sketch, define fixed part locations, planes, and so on, then design the parts referencing these definitions.
For example, you can insert a part in an assembly, then build a fixture based on this part. Working top-down, creating the fixture in context, allows you to reference model geometry, so you can control the dimensions of the fixture by creating geometric relations to the original part. That way, if you change a dimension of the part, the fixture automatically is updated.