Standard mates (coincident, concentric, distance) in Solidworks - Deep Dive

Overview - Standard mates (coincident, concentric, distance)

What is it?

Standard mates in SolidWorks are rules that connect parts in an assembly to control how they fit and move together. The coincident mate aligns two faces or edges so they touch exactly. The concentric mate aligns two circular edges or holes so they share the same center. The distance mate sets a fixed space between two parts. These mates help build realistic and functional assemblies.

Why it matters

Without standard mates, parts in an assembly would float freely or overlap incorrectly, making it impossible to design machines or products accurately. These mates solve the problem of positioning parts precisely, ensuring they fit and move as intended. This saves time, reduces errors, and helps engineers communicate designs clearly.

Where it fits

Before learning standard mates, you should understand basic SolidWorks navigation and part creation. After mastering these mates, you can learn advanced mates, motion studies, and assembly analysis to simulate real-world behavior.

Mental Model

Core Idea

Standard mates are like invisible connectors that lock parts together by aligning faces, centers, or setting distances to build a stable assembly.

Think of it like...

Imagine building a puzzle: coincident mates are like snapping two puzzle pieces edge-to-edge, concentric mates are like stacking rings perfectly centered on a stick, and distance mates are like placing two magnets a fixed space apart.

Assembly Mates Structure:

+-------------------+
|   Assembly Parts  |
+-------------------+
         |
         v
+-------------------+
|   Standard Mates  |
+-------------------+
| Coincident       |
| Concentric       |
| Distance         |
+-------------------+

Build-Up - 6 Steps

1

Foundation

Understanding Coincident Mate Basics

Concept: Introduce the coincident mate that aligns two faces or edges to touch exactly.

In SolidWorks, a coincident mate forces two selected faces or edges to lie on the same plane and touch. For example, if you select the flat face of one part and the flat face of another, applying a coincident mate will make them flush together with no gap.

Result

The two parts become connected so their selected faces or edges touch perfectly without any space.

Understanding coincident mates is essential because it forms the foundation for positioning parts precisely in assemblies.

2

Foundation

Learning Concentric Mate Fundamentals

Concept: Explain the concentric mate that aligns circular edges or holes sharing the same center axis.

A concentric mate aligns two circular edges, such as holes or cylindrical faces, so their centers and axes match. For example, aligning a bolt hole on one part with a hole on another ensures the bolt fits perfectly through both.

Result

The parts rotate or slide around the shared center axis but remain aligned concentrically.

Knowing concentric mates helps create assemblies where parts fit together around a common axis, like shafts and bearings.

3

Intermediate

Applying Distance Mate for Spacing

Concept: Introduce the distance mate to set a fixed gap between two parts or faces.

The distance mate lets you specify an exact measurement between two selected faces, edges, or points. For example, you can keep two plates exactly 10 mm apart by applying a distance mate with that value.

Result

The parts maintain the specified gap, preventing them from touching or moving closer.

Distance mates are crucial for controlling clearances and ensuring parts do not interfere in assemblies.

4

Intermediate

Combining Mates for Complex Positioning

🤔Before reading on: do you think you can position a cylindrical part inside a hole using only one mate or multiple mates? Commit to your answer.

Concept: Show how combining coincident and concentric mates positions parts fully in 3D space.

To place a pin inside a hole, first apply a concentric mate to align their centers. Then apply a coincident mate between one end face of the pin and the hole face to fix its position along the axis. This combination locks the pin in place without floating.

Result

The pin fits perfectly inside the hole, aligned and fixed in position.

Understanding how mates work together allows precise control over part placement beyond simple alignment.

5

Advanced

Managing Degrees of Freedom with Mates

🤔Before reading on: do you think one concentric mate fully fixes a cylindrical part in place or allows some movement? Commit to your answer.

Concept: Explain how mates restrict movement and how some allow rotation or translation.

A single concentric mate aligns centers but allows rotation around the axis and sliding along it. Adding a coincident mate on an end face removes sliding. Knowing which mates restrict which movements helps control part behavior in assemblies.

Result

You can predict and control how parts move or stay fixed based on mate combinations.

Knowing degrees of freedom helps prevent unintended part movement and ensures assembly stability.

6

Expert

Avoiding Overdefined and Conflicting Mates

🤔Before reading on: do you think adding more mates always makes assemblies more stable or can it cause errors? Commit to your answer.

Concept: Discuss how too many mates can conflict and cause errors called overdefined assemblies.

If mates contradict each other, like two distance mates setting different gaps between the same faces, SolidWorks flags an error. Experts carefully plan mates to avoid conflicts and use mate diagnostics tools to fix issues.

Result

Assemblies remain stable and error-free, improving design reliability.

Understanding mate conflicts prevents wasted time troubleshooting and ensures smooth assembly workflows.

Under the Hood

SolidWorks mates work by mathematically constraining the degrees of freedom of parts in 3D space. Each mate adds equations that restrict translation or rotation along axes. The software solves these constraints simultaneously to position parts correctly. Coincident mates align planes or edges, concentric mates align axes, and distance mates fix spacing. The solver updates positions dynamically as mates or parts change.

Why designed this way?

This constraint-based approach allows flexible yet precise control over assemblies. Early CAD systems used manual positioning, which was error-prone. Constraint solving automates alignment and enforces design intent. Alternatives like fixed positioning lack flexibility. The tradeoff is complexity in managing conflicting mates, but the benefits in accuracy and automation outweigh this.

+-----------------------+
|   Assembly Solver      |
+-----------------------+
| Constraints:          |
| - Coincident (face)   |
| - Concentric (axis)   |
| - Distance (gap)      |
+-----------------------+
          |
          v
+-----------------------+
| Part Positions & Moves|
+-----------------------+

Myth Busters - 4 Common Misconceptions

Quick: Does a single concentric mate fully lock a cylindrical part in place? Commit yes or no.

Common Belief: One concentric mate completely fixes a cylindrical part so it cannot move.

Reality: A single concentric mate aligns centers but allows rotation and sliding along the axis.

Why it matters: Assuming full fixation leads to unexpected part movement and unstable assemblies.

Quick: Can you add unlimited mates without errors? Commit yes or no.

Common Belief: Adding more mates always makes the assembly more stable and accurate.

Reality: Too many or conflicting mates cause overdefined errors and prevent assembly solving.

Why it matters: Ignoring this causes wasted time fixing errors and confusion in assembly behavior.

Quick: Does a distance mate always keep parts from touching? Commit yes or no.

Common Belief: Distance mates prevent any contact between parts by maintaining a gap.

Reality: Distance mates fix a gap but if set to zero, parts become coincident and can touch.

Why it matters: Misunderstanding this can cause parts to overlap or interfere unintentionally.

Quick: Are mates only for positioning parts, not for controlling movement? Commit yes or no.

Common Belief: Mates only position parts but do not control how they move relative to each other.

Reality: Mates define allowed movements by restricting degrees of freedom, enabling motion control.

Why it matters: Missing this limits the ability to simulate real-world part interactions in assemblies.

Expert Zone

1

Concentric mates allow rotation and translation along the axis unless combined with other mates to restrict movement.

2

Distance mates can be driven or driving dimensions, allowing dynamic control or fixed spacing depending on design needs.

3

Overdefined assemblies often arise from redundant mates; using mate groups and folders helps manage complexity.

When NOT to use

Standard mates are not suitable for flexible or deformable parts; in such cases, use advanced motion studies or flexible subassemblies. Also, avoid using too many distance mates for complex positioning; instead, use reference geometry or patterns.

Production Patterns

In professional assemblies, engineers combine concentric and coincident mates to simulate real mechanical joints like pins and holes. Distance mates control clearances for thermal expansion. Mate diagnostics and suppression are used to manage large assemblies efficiently.

Connections

Constraint Solving in Robotics

Both use mathematical constraints to control movement and position of parts or joints.

Understanding mates in SolidWorks helps grasp how robots calculate joint limits and positions for precise motion.

Mechanical Linkages in Engineering

Mates model physical connections like hinges and sliders in mechanical linkages.

Knowing mates deepens understanding of how real machines transfer motion through connected parts.

Graph Theory in Computer Science

Assemblies with mates can be seen as graphs where parts are nodes and mates are edges defining connections.

Viewing assemblies as graphs helps analyze connectivity and detect conflicts or isolated parts.

Common Pitfalls

#1 Assuming one concentric mate fully fixes a cylindrical part.

Wrong approach:

Apply only a concentric mate between a pin and hole and expect no movement.

Correct approach:

Apply a concentric mate plus a coincident mate on an end face to fix position along the axis.

Root cause:

Misunderstanding degrees of freedom allowed by each mate type.

#2 Adding conflicting distance mates causing overdefined errors.

Wrong approach:

Apply two different distance mates between the same two faces with different values.

Correct approach:

Use only one distance mate or adjust mates to avoid conflicting constraints.

Root cause:

Not recognizing that mates add mathematical constraints that can conflict.

#3 Using distance mate with zero value expecting parts to stay apart.

Wrong approach:

Set distance mate to 0 mm to keep parts separated.

Correct approach:

Set distance mate to a positive value greater than zero to maintain gap.

Root cause:

Confusing zero distance with a gap instead of coincident placement.

Key Takeaways

Standard mates in SolidWorks control how parts fit and move by aligning faces, centers, or setting distances.

Coincident mates make faces or edges touch exactly, concentric mates align circular centers, and distance mates fix gaps.

Mates restrict degrees of freedom, so combining them controls part movement and assembly stability.

Too many or conflicting mates cause errors; careful planning and diagnostics prevent assembly problems.

Understanding mates connects to broader concepts like constraint solving and mechanical linkages, enriching design skills.

Practice

1. Which type of standard mate in SolidWorks makes two faces or edges touch exactly?

easy

A. Coincident mate

B. Concentric mate

C. Distance mate

D. Parallel mate

Solution

1. Step 1: Understand the Coincident Mate

   A coincident mate forces two faces or edges to touch exactly, aligning them perfectly.

2. Step 2: Compare with Other Mates

   Concentric mates align circular parts along the same axis, and distance mates keep parts a fixed space apart, so they do not make faces touch.

3. Final Answer:

   Coincident mate -> Option A

4. Quick Check:

   Faces touching = Coincident mate [OK]

Hint: Faces or edges touching? Choose coincident mate [OK]

Common Mistakes:

• Confusing concentric with coincident
• Thinking distance mate makes parts touch
• Mixing parallel mate with coincident

2. Which of the following is the correct syntax to apply a concentric mate between two circular edges in SolidWorks?

easy

A. Mate.AlignCenters(edge1, edge2)

B. Mate.Add(edge1, edge2, 'distance')

C. Mate.SelectFaces(face1, face2).ApplyCoincident()

D. Mate.SelectEdges(edge1, edge2).ApplyConcentric()

Solution

1. Step 1: Identify the correct method for concentric mates

   The method to apply a concentric mate involves selecting edges and applying the concentric constraint, matching Mate.SelectEdges(edge1, edge2).ApplyConcentric().

2. Step 2: Eliminate incorrect options

   Mate.Add(edge1, edge2, 'distance') applies a distance mate, Mate.SelectFaces(face1, face2).ApplyCoincident() applies coincident on faces, and Mate.AlignCenters(edge1, edge2) is not a valid SolidWorks syntax.

3. Final Answer:

   Mate.SelectEdges(edge1, edge2).ApplyConcentric() -> Option D

4. Quick Check:

   Concentric mate syntax = Mate.SelectEdges(edge1, edge2).ApplyConcentric() [OK]

Hint: Select edges then apply concentric mate method [OK]

Common Mistakes:

• Using face selection for concentric mate
• Confusing distance mate syntax with concentric
• Using non-existent methods like AlignCenters

3. Given two cylindrical parts with axes aligned, what is the result of applying a concentric mate between their circular edges?

medium

A. The parts are fixed at a set distance apart.

B. The parts' axes align and their circular edges share the same center axis.

C. The parts' flat faces touch exactly.

D. The parts rotate freely without alignment.

Solution

1. Step 1: Understand the effect of a concentric mate

   A concentric mate aligns the axes of circular edges so they share the same center line.

2. Step 2: Compare with other mate effects

   Distance mates keep parts apart, coincident mates make faces touch, and free rotation means no mate applied.

3. Final Answer:

   The parts' axes align and their circular edges share the same center axis. -> Option B

4. Quick Check:

   Concentric mate aligns axes = The parts' axes align and their circular edges share the same center axis. [OK]

Hint: Concentric mate aligns circular axes, not faces [OK]

Common Mistakes:

• Thinking concentric sets distance
• Confusing coincident with concentric
• Assuming free rotation after mate

4. You tried to apply a distance mate between two parts but the parts snap together instead of staying apart. What is the likely cause?

medium

A. The distance value was set to zero.

B. You applied a coincident mate instead of a distance mate.

C. The parts are fixed and cannot move.

D. You applied a concentric mate by mistake.

Solution

1. Step 1: Check the distance mate value

   If the distance is zero, parts will snap together, appearing coincident.

2. Step 2: Rule out other causes

   Applying coincident or concentric mates causes different behaviors; fixed parts do not move but distance mate with zero causes snapping.

3. Final Answer:

   The distance value was set to zero. -> Option A

4. Quick Check:

   Distance zero snaps parts together = The distance value was set to zero. [OK]

Hint: Check distance value; zero means no gap [OK]

Common Mistakes:

• Confusing coincident with distance mate effect
• Ignoring zero distance input
• Assuming concentric mate affects distance

5. You need to assemble a shaft inside a hole so that the shaft's axis aligns with the hole's axis and the shaft is exactly 5 mm away from the hole's bottom face. Which mates should you apply?

hard

A. Apply a distance mate of 5 mm between shaft and hole edges only.

B. Apply two coincident mates: one for axes and one for bottom faces.

C. Apply a concentric mate between shaft and hole edges, then a distance mate of 5 mm between shaft bottom face and hole bottom face.

D. Apply a concentric mate and a coincident mate between bottom faces.

Solution

1. Step 1: Align shaft and hole axes

   Use a concentric mate between the circular edges of shaft and hole to align their axes.

2. Step 2: Set the gap distance

   Apply a distance mate of 5 mm between the shaft's bottom face and the hole's bottom face to maintain the required space.

3. Final Answer:

   Apply a concentric mate between shaft and hole edges, then a distance mate of 5 mm between shaft bottom face and hole bottom face. -> Option C

4. Quick Check:

   Concentric for axis + distance for gap = Apply a concentric mate between shaft and hole edges, then a distance mate of 5 mm between shaft bottom face and hole bottom face. [OK]

Hint: Use concentric for alignment, distance for spacing [OK]

Common Mistakes:

• Using coincident mate for axis alignment
• Applying distance mate between edges only
• Mixing coincident and concentric incorrectly