2009

Top-Down Assembly Design
When you design from the top down, you begin with design criteria and create
components that meet those criteria. Designers list known parameters and
may create an engineering layout (a 2D design that evolves throughout the
design process).
A layout can include contextual items such as the walls and floor where an
assembly will stand, machinery that feeds into or receives output from the
assembly design, and other fixed data. Other criteria such as mechanistic
characteristics may also be included in the layout. You can sketch the layout
in a part file, then place it in the assembly file. You develop sketches into
features as the design evolves.
The final assembly is a collection of interrelated parts that are uniquely
designed to solve the current design problem.
Middle-Out Assembly Design
Most assembly modeling combines the strategies of bottom-up and top-down
design. Some requirements are known and some standard components are
used, but new designs must also be produced to meet specific objectives.
Usually, you begin with some existing components and design other parts as
required. You analyze the design intent, then insert or create the grounded
(base) component. As you develop the assembly, you place components or
create new ones in place, as required.
Assembly Coordinate System
A new assembly file has three default work planes and work axes. The point
of intersection of the work axes is the origin of the assembly coordinate system.
In the browser, the default work planes, work axes, and the center points are
listed under the Origin icon. These features are initially hidden in the graphics
window, but you can right-click them in the browser and select Visibility to
display them. You can constrain components to the work planes and the
origin.
In the following illustration, visibility has been activated for the assembly
default work planes, axes, and center point, with the default isometric view.
Assembly Coordinate System | 133