Under-defined vs fully-defined vs over-defined in Solidworks - Compared

Introduction

This feature helps you understand how sketches in SolidWorks are constrained. It shows if a sketch has too few, just enough, or too many constraints. This helps you create stable and accurate designs.

When you start drawing a new sketch and want to check if it is stable.

When your sketch moves unexpectedly and you want to find missing constraints.

When you add constraints and want to avoid conflicts that cause errors.

When preparing a sketch for 3D features like extrude or revolve.

When reviewing a design to ensure all parts are properly defined.

Steps

Step 1: Open

- SolidWorks and create or open a sketch

The sketch appears in the graphics area ready for editing

Step 2: Look at the status bar at the bottom of the SolidWorks window

- Status bar

You see a message indicating if the sketch is under-defined, fully-defined, or over-defined

Step 3: Select the sketch entities

- Graphics area

Sketch entities highlight with colors showing their constraint status: blue for under-defined, black for fully-defined, red for over-defined

Step 4: Add or remove constraints

- Sketch tab > Add Relations or Delete Relations

Sketch updates and status bar message changes accordingly

Step 5: Use the 'Display/Delete Relations' tool

- Sketch tab > Display/Delete Relations

A list of all constraints appears, helping you identify conflicts or missing constraints

Before vs After

Before

Sketch entities are blue and status bar shows 'Under-defined'. The sketch moves when dragged.

After

Sketch entities turn black and status bar shows 'Fully-defined'. The sketch stays fixed when dragged.

Settings Reference

Sketch Status Display

📍 Status bar at the bottom of the SolidWorks window

Shows the current constraint state of the sketch

Default: Under-defined when sketch is first created

Entity Color Coding

📍 Sketch tab > Options > System Options > Colors

Visually indicates the constraint status of sketch entities

Default: Blue for under-defined, Black for fully-defined, Red for over-defined

Display/Delete Relations

📍 Sketch tab

Helps manage and troubleshoot sketch constraints

Default: Show all constraints

Common Mistakes

Ignoring the status bar message and continuing to add features.

An under-defined sketch can cause unexpected changes in the model later.

Always check and fix sketch constraints until it is fully-defined before proceeding.

Adding too many constraints causing the sketch to become over-defined.

Over-defined sketches cause errors and prevent proper editing.

Use the Display/Delete Relations tool to find and remove conflicting constraints.

Summary

Sketches can be under-defined, fully-defined, or over-defined based on constraints.

Fully-defined sketches are stable and best for building features.

Use color codes and status bar messages to monitor sketch constraint status.

Practice

1.

Which of the following best describes a fully-defined sketch in SolidWorks?

easy

A. The sketch has conflicting constraints causing errors.

B. The sketch has too few constraints and can still move or change.

C. The sketch is missing all constraints and is free to move.

D. The sketch has just enough constraints to fix its position and shape.

Solution

1. Step 1: Understand sketch constraint types

   Under-defined means not enough constraints, fully-defined means just enough, and over-defined means too many constraints causing conflicts.

2. Step 2: Identify fully-defined sketch meaning

   A fully-defined sketch is fixed in place with no degrees of freedom left, meaning it has just enough constraints.

3. Final Answer:

   The sketch has just enough constraints to fix its position and shape. -> Option D

4. Quick Check:

   Fully-defined = just right constraints [OK]

Hint: Fully-defined means no movement possible [OK]

Common Mistakes:

• Confusing fully-defined with over-defined
• Thinking fully-defined means no constraints
• Assuming under-defined is fixed

2.

Which of these constraint sets will cause a sketch to be over-defined?

1. Horizontal line fixed length
2. Horizontal line fixed length + another length constraint on same line
3. Vertical line with one length constraint
4. Circle with radius constraint only

easy

A. Option 3 only

B. Option 2 only

C. Option 4 only

D. Option 1 only

Solution

1. Step 1: Analyze constraints for over-definition

   Over-defined means conflicting or redundant constraints. Option 2 has two length constraints on the same line, causing conflict.

2. Step 2: Check other options

   Options 1, 3, and 4 have only one constraint per element, so they are not over-defined.

3. Final Answer:

   Option 2 only -> Option B

4. Quick Check:

   Multiple conflicting constraints = over-defined [OK]

Hint: Two constraints on same element cause over-defined [OK]

Common Mistakes:

• Thinking one constraint is over-defined
• Confusing under-defined with over-defined
• Ignoring conflicting constraints

3.

Given a sketch with a rectangle where only two adjacent sides have length constraints and no other constraints, what is the sketch state?

medium

A. Under-defined

B. Fixed

C. Over-defined

D. Fully-defined

Solution

1. Step 1: Identify constraints on rectangle

   Two adjacent sides have length constraints, but no position or angle constraints are given.

2. Step 2: Determine sketch freedom

   Without fixing position or angles, the rectangle can still move or rotate, so it is under-defined.

3. Final Answer:

   Under-defined -> Option A

4. Quick Check:

   Not enough constraints = under-defined [OK]

Hint: Missing position constraints means under-defined [OK]

Common Mistakes:

• Assuming length constraints alone fully define sketch
• Confusing fixed with fully-defined
• Ignoring degrees of freedom like rotation

4.

Look at this sketch constraint setup:

1. A line fixed length 50mm
2. Another length constraint 60mm on the same line
3. Horizontal constraint on the line

What is the problem and how to fix it?

medium

A. Over-defined due to conflicting length constraints; remove one length constraint.

B. Under-defined because horizontal constraint is missing; add horizontal constraint.

C. Fully-defined; no problem exists.

D. Over-defined due to missing horizontal constraint; add horizontal constraint.

Solution

1. Step 1: Identify conflicting constraints

   The line has two different length constraints (50mm and 60mm), which conflict and cause over-definition.

2. Step 2: Fix by removing conflict

   Removing one length constraint resolves the conflict and fixes the over-defined state.

3. Final Answer:

   Over-defined due to conflicting length constraints; remove one length constraint. -> Option A

4. Quick Check:

   Conflicting constraints cause over-defined [OK]

Hint: Remove conflicting constraints to fix over-defined [OK]

Common Mistakes:

• Adding more constraints instead of removing
• Ignoring conflicting lengths
• Assuming horizontal constraint fixes over-definition

5.

You have a sketch of a triangle with all three sides length constrained and one angle constrained between two sides. The sketch still shows as under-defined. What could be the reason?

hard

A. The sketch is over-defined due to too many constraints on sides.

B. The angle constraint conflicts with side lengths causing errors.

C. The triangle can still move or rotate because position constraints are missing.

D. All constraints fully define the sketch; this is a software bug.

Solution

1. Step 1: Analyze given constraints

   All sides have length constraints and one angle is fixed, but no constraints fix the triangle's position in the plane.

2. Step 2: Understand under-defined cause

   Without fixing position (like fixing a point or adding horizontal/vertical constraints), the sketch can still move or rotate, so it remains under-defined.

3. Final Answer:

   The triangle can still move or rotate because position constraints are missing. -> Option C

4. Quick Check:

   Missing position constraints cause under-defined [OK]

Hint: Fix position to fully define sketch [OK]

Common Mistakes:

• Assuming side lengths alone fully define sketch
• Confusing over-defined with under-defined
• Ignoring need for position constraints