‍Video 1: The fundamentals of sketching, including creating and managing sketches.

Video 2: Adding sketch entities and applying sketch relations.

Video 3: Using dimensions to define sketches accurately and maintain parametric control.

In this post, we will take our sketches to the next level by discussing defined, underdefined, and overdefined sketches. Understanding how SolidWorks handles these different sketch states is crucial for producing robust, error-free designs.

What Do Sketch Colours Mean in SolidWorks ?

As you create sketches in SolidWorks , you may notice that the colour of sketch entities changes based on their definition state. This visual feedback is extremely helpful in understanding whether your sketch is complete, needs more constraints, or contains conflicting information.

  • Blue (Underdefined) – The sketch is incomplete, meaning SOLIDWORKS does not yet know the exact size or position of certain entities.
  • Black (Fully Defined) – The sketch is fully constrained, with all dimensions and relations specified.
  • Red (Overdefined) – The sketch contains conflicting or excessive constraints, causing errors.

The goal of sketching in SolidWorks is to ensure that each sketch is fully defined (black), meaning every entity is positioned exactly as intended.

Understanding Underdefined Sketches

An underdefined sketch occurs when SolidWorks does not have enough information to determine the exact position or size of one or more sketch entities. This can be confirmed in multiple ways:

  1. Sketch Colour – Entities appear blue.
  2. Feature Manager Design Tree – The sketch name will display a small minus (-) symbol, indicating underdefinition.
  3. Status Bar – The bottom-right of the screen will say Underdefined.

How to Fix an Underdefined Sketch

To identify what is underdefined, try clicking and dragging different parts of the sketch. If an entity moves freely, it means it lacks either a dimension or a relation.

For example, let’s say we have a line that is underdefined. We can define it by:

  • Adding a dimension to specify its length.
  • Applying relations to fix it in place, such as coincident with another entity.

Interestingly, adding a dimension doesn’t always have to be on the underdefined entity itself. Sometimes, defining a neighbouring entity will indirectly constrain the underdefined one.

What is a Fully Defined Sketch?

A fully defined sketch means SolidWorks has all the information it needs to accurately represent your design. A quick checklist for fully defining sketches includes:

  • All sketch entities appear black.
  • No missing dimensions or relations.
  • The Feature Manager Design Tree no longer shows a minus (-) symbol next to the sketch.
  • The status bar at the bottom-right says "Fully Defined".

Ensuring a sketch is fully defined is good practice, as it prevents unexpected changes when features are modified.

How Sketches Become Overdefined

An overdefined sketch occurs when too many constraints or conflicting dimensions are applied. SolidWorks indicates this in several ways:

  • Red Entities – Overdefined constraints appear in red.
  • Amber Warnings – Some areas may show amber highlights, indicating potential conflicts.
  • Status Bar Warning – The bottom-right corner displays Overdefined along with a warning symbol.

Overdefinition usually happens when:

  • A new dimension conflicts with an existing one.
  • Extra relations are added that contradict each other.
  • Automatic relations were inadvertently applied during sketching.

For example, if a line already has a fixed length, but a second, contradictory length is applied, the sketch becomes overdefined.

How to Fix an Overdefined Sketch

SolidWorks helps resolve overdefined sketches by offering the option to convert conflicting dimensions into driven dimensions. A driven dimension is purely a reference and does not control the sketch geometry.

To fix an overdefined sketch:

  1. Check the red-highlighted areas to identify conflicts.
  2. Delete unnecessary or conflicting dimensions by selecting and pressing Delete.
  3. Convert redundant dimensions to "Driven" by right-clicking and selecting "Driven Dimension".
  4. Use the Undo feature (Ctrl+Z) if the issue occurred due to a recent addition.

By carefully adding dimensions and relations, you can avoid overdefining your sketches and keep them stable.

Exiting and Accepting a Sketch in SolidWorks

Once a sketch is fully defined, you may need to exit and accept it. Often, sketches are used directly for creating features, meaning there is no need to manually exit them. However, in cases where sketches are used for construction geometry or advanced feature creation, knowing how to exit a sketch is essential.

Ways to Exit a Sketch

  • Click the Sketch Button in the Sketch tab (which will now say "Exit Sketch").
  • Use the confirmation corner icons in the top-right of the viewport. Be careful to select the green checkmark and not the red cross, which will discard changes.
  • Use the right-click menu to quickly exit a sketch.

Speeding up your workflow by using shortcuts or the right-click menu can enhance efficiency, especially when working with multiple sketches.

Final Thoughts: Bringing It All Together

Over the course of this series, we have covered all the fundamental aspects of SolidWorks sketching:

  • Video 1 introduced the basics of sketching, including creating and managing sketches.
  • Video 2 explored adding sketch entities and applying sketch relations to maintain geometric constraints.
  • Video 3 focused on dimensions and how they control the scale and accuracy of a sketch.
  • Video 4 (this post) explained defined, underdefined, and overdefined sketches, ensuring that each sketch is properly constrained and free from errors.

Understanding sketch definitions is critical for creating robust, parametric designs in SOLIDWORKS. Ensuring a sketch is fully defined prevents issues later in the design process, allowing for easy modifications without unwanted changes.

If you’re following this series, you are now well-equipped to start creating fully defined and well-structured sketches in SOLIDWORKS. From here, you can begin exploring 3D feature creation, where sketches serve as the foundation for extrusions, revolves, lofts, and more.

Stay tuned for more SolidWorks tips, and happy modelling!