T-FLEX Parametric CAD. Fundamentals. 2D Design

Fundamentals. Two-Dimensional Design
“TOP-DOWN” DESIGN
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When using the “Top-down” design approach, separate parts-fragments are created directly within the
assembly drawing window while working with the assembly. There are two approaches to creating a
fragment when using the “Top-down” method - fragment extraction and working in the assembly context.
In the first case, a fragment can be created by extracting into a separate file the necessary elements of the
assembly drawing. The second case allows creating a new part drawing with the provision for referencing
existing elements of the assembly drawing.
The fragments created in this way can be attached to the elements of the assembly itself or other existing
fragments. This helps excluding or significantly reducing use of external variables and simplifies handling of
an assembly. Meanwhile, some values of the original model parameters can be obtained directly from the
assembly context. This approach significantly simplifies relating elements with each other and provides
parametric relation between those. If dimensions or position of one of the parts is modified, then all related
model elements will adjust automatically.
Working in the assembly context simplifies in certain cases the design process of the assembly module. This
also facilitates development of the complete documentation suite of such a module, including detail drawings
of all contributing fragment parts. Upon modifications to any assembly document, either the assembly
drawing itself or one of its fragments, the changes propagate to all documents of the assembly (automatically
or by the user request). As a result, modifications to one part cause update of the full suite of new
documentation for the assembly, including the assembly drawing itself and detail drawings of all
contributing part fragments.
The “Top-down” design approach may not be suitable in all cases of designing assemblies. The method has
certain shortcomings that limit its use:
• More complicated organization, compared with the approach “from part to assembly”;
• Lesser robustness to topology changes. For example, once an assembly line is referenced by an
introduced fragment, it can no longer be deleted, otherwise the fragment associative reference will be
lost;
• This approach is less convenient in terms of reusing fragments in other assemblies, since modifying a
fragment may be complicated without the availability of references to the original assembly;
• Upon an attempt to extract a fragment, if it is impossible to “detach” an element from the assembly
drawing, additional copies of the necessary elements are created in order to preserve parametric
relations in the assembly drawing;
• Somewhat higher computational resources are required.
The icons for handling the “Top-down” approach can be found:
• In the textual Menu "File|Fragment|...";
• In the automenu of the command “FR: Create Fragment”:
Create new Fragment in Assembly Context
Extract Fragment Drawing