Things to Remember: CAD References
Carefully choose references.
This includes references for sketching planes, sketch orientation, sketcher references, edges or surfaces for rounds, etc.
Choose references that follow the design intent.
- Though it’s easy to make all your features reference only the base datum planes, the model won’t follow when modifications are made. Choose references that allow the model to “move” with the intent as changes are made.
- In Practice: Think about the design intent and choose references that are stable and reflect that intent.
Choose references that won’t disappear.
- References like edges that disappear when rounded are not usually the best choice. Datums and planner surfaces are typically better. References from base features are typically more stable than those of later ones.
Choose references sparingly.
- More references mean more feature interconnectivity which can make the model more difficult to work with. However, choose enough references to make the model follow design intent.
- In Practice: Some models are so tightly tied with references that the model fails with almost any modification. Choices like Thru Next have no references.
When several features are to reference the same thing (like a planer surface or axis), create datums for control.
- Key datums (planes, points, axes) are easier to find and select when they are named. Named features also denote significance for someone changing the model later. Name your important datums.
When several aspects of a part must interact build control features like curve sets to manage the interactions, then reference them with the features.
- This can apply to features such as cuts and protrusions to allow wall thickness and spacing.
Create relations that associate features when direct references are not practical.
- In Practice: When writing relations, use comments for “what” and “why”. If other people use the model, they’ll be more impressed if you are specific in your comments.
Drafts and rounds/fillets/chamfers are often best left to the end of the model.
- Although this is a good rule, there are times when they are required earlier. Care should be given to where the features are inserted in the model tree.
Rounds should normally be inserted as unique features rather than put in a sketch.
- This is a good rule of thumb, but there are times where a round can’t be created or a dimensioning scheme (design intent) requires the radius in a sketch. As above, carefully consider when. (The same is true for Drafts, Chamfers, etc.)
- In Practice: It is often good to build models without drafts and rounds, then go back using Insert Mode to put them in — where possible clustering them with the parent features.
When the above guidelines don’t make sense, carefully consider your options.
Good modeling practices are far more important early in the model than at the end when you’re trying to put in the last round or draft.