Mastering Large Assemblies in CAD
We have all been there. You are on a tight deadline for a project, perhaps designing a complex piece of mining equipment for a site in WA or a custom architectural fit-out in Melbourne. You go to rotate your model, and suddenly—everything freezes. The cursor spins, and your productivity grinds to a halt.
In the world of Computer-Aided Design (CAD), particularly with software like SOLIDWORKS, this is known as the "Large Assembly" problem. But what exactly constitutes a large assembly, and more importantly, how do we fix it without simply throwing money at expensive new hardware?
In this post, we’ll break down the definition of large assemblies, the root causes of performance lag, and the best design practices to keep your workflow moving efficiently.
What Defines a "Large Assembly"?
The term "large assembly" means different things to different people. It isn’t strictly defined by the number of components or the file size on your hard drive. Instead, a large assembly is defined by its behaviour.
An assembly is considered "large" if:
It maximises or exhausts your system resources (RAM and CPU).
It significantly hinders your productivity.
These issues are usually caused by two main factors: Physical Size and Complexity.
1. Physically Large
This refers to assemblies that require significant layout work or engineering input to position components. It involves managing such a high volume of parts that the calculation and memory requirements naturally slow down the system.
2. Complexity
Often, the physical size isn't the culprit—it’s the data complexity. This includes:
Parametric Relationships: Too many interconnected links between files.
Mates: A high volume of top-level mates solving simultaneously.
Mixed Disciplines: Combining mechanical components, Toolbox parts, library parts, weldments, routed systems (piping/cabling), and imported data from subcontractors.
Geometric Complexity: Parts that are difficult for the graphics card to rebuild or render.
The 80/20 Rule of Performance
When CAD performance drops, the knee-jerk reaction is often to blame the computer. "I need a faster processor" or "I need more RAM" are common complaints. However, upgrading hardware is often a waste of money if the underlying modelling practices are poor.
Think of it this way: Putting a learner driver in a V8 Supercar doesn't make them a race driver.
Performance issues generally break down as follows:
20% (Software & Hardware): These are things under the software’s control, such as bugs, algorithms, code efficiency, and your PC specs.
80% (User Control): This is under your control. It includes file management options, setup, and most importantly, modelling methodology.
While using certified hardware is recommended, major performance issues usually arise from modelling practices rather than hardware limitations.
Signs Your Assembly is Struggling
You know you have a large assembly problem when you experience significant lag in:
Opening, closing, and saving files.
Rebuild times.
Creating drawing views.
Rotating, panning, and zooming.
Inserting new components.
Switching between parts, assemblies, and drawings.
Best Design Practices for Australian Designers
There is no "magic button" to fix a slow assembly. A sluggish model is usually the result of an accumulation of small inefficiencies. To fix it, we need a strategy that covers parts, assemblies, and data management.
1. Effective Part Modelling
Performance starts at the part level. If your individual bricks are heavy, the house will be heavy.
Proper Origin: ensure your part is modelled logically around the origin.
Simplicity: Use easy-to-build features and avoid unnecessary complex geometry.
Clean References: Remove in-context relationships that are no longer needed and strictly avoid circular references (where Part A references Part B, and Part B references Part A).
Simplified Versions: Create configurations of complex parts that suppress unnecessary details (like threads or internal fillets) for use in the main assembly.
2. Effective Assembly Modelling
How you put the puzzle together matters.
Sub-assemblies: Organise your tree! Don't leave hundreds of loose parts at the top level. Group them into logical sub-assemblies.
Mates: Use proper mating techniques. Avoid mating to geometry that might change; mate to planes where possible.
Load Less Data: Use tools designed to reduce memory load:
Quick Open / Large Design Review: For quickly viewing and measuring.
Lightweight Mode: Loads only the graphical data, not the heavy parametric data.
SpeedPak: A simplified representation of the assembly.
Draft Quality: Use draft quality in drawings to speed up view creation.
3. File Management & Collaboration
In a team environment, how you manage data is crucial.
Access: Ensure all design team members have access to the necessary files.
Protection: Protect files from being accidentally overwritten by non-design staff or colleagues.
Metadata: Ensure file properties are filled out correctly to aid in searching and BOM creation.
Avoid "Stuck" Files: Poor file management leads to lost files, working on the wrong version, or network bottlenecks.
The Bottom Line
There is no quick fix for a slow, large assembly. It requires a disciplined approach to design. By understanding how the software works in the background and adhering to these best practices, you can control the "root cause" of the lag.
Whether you are in Sydney, Brisbane, or the bush, efficiency in design saves time and frustration. Start implementing these strategies today, and you will see that a smarter approach beats a faster computer every time.
Stay tuned for our next blog where we will dive deeper into specific step-by-step methods for simplifying complex geometry.