Cad

name: cad

description: > Expert CAD assistant for engineers and designers. Use this skill whenever the user needs: help with computer-aided design, 3D modeling, parametric design, assembly modeling, or generating manufacturing outputs. Includes both software usage and design methodology. trigger: Any engineering design problem involving CAD - from concept to manufacturing. license: MIT compatibility: opencode metadata: audience: engineers category: engineering

Computer-Aided Design — Principles and Practice

Covers: 3D Modeling · Parametric Design · Assemblies · Manufacturing · Standards · Best Practices

CAD Fundamentals

What is CAD?

Computer-Aided Design: creation, modification, analysis, and optimization of designs digitally.

CAD Benefits

• Faster iteration
• Easy versioning
• Simulation integration
• Manufacturing automation
• Collaboration

2D vs 3D

2D: Drawings, schematics 3D: Parts, assemblies, visualization

Direct vs Parametric

Direct modeling: Push/pull faces, edit geometry directly.

Parametric modeling: Dimensions and relations drive geometry.

• Changes propagate automatically
• Design intent preserved

History-Based Modeling

Feature tree records all operations:

• Easy to edit
• Non-destructive

Feature-Based Modeling

Common operations as features:

• Extrude, sweep, loft
• Hole, fillet, chamfer
• Shell, rib, draft

Feature Order

Dependent features after dependencies:

• Chronological tree
• Rollback to edit

Design Intent

How model responds to changes:

• Dimensions vs. relations
• Equations link dimensions

Sketches

2D profiles for 3D features:

• Constrain geometry
• Define relationships

Sketch Constraints

Underdefined

Degrees of freedom remain:

• May cause issues
• Add constraints

Fully Defined

All DOF constrained:

• Blue (under) → Black (fully)
• Stable model

Overdefined

Conflicting constraints:

• Must resolve
• Delete or edit

Dimensions

• Reference (driven)
• Driven (from geometry)
• Driving (controls geometry)

3D Feature Operations

Extrude

Project sketch along direction:

• Distance or through all
• Taper angle
• Direction (one/both)

Revolve

Rotate sketch around axis:

• Full 360 or angle
• Axis selection

Sweep

Extrude along path:

• Guide curves
• Smooth transitions

Loft

Blend between profiles:

• Guide curves help
• Can be tricky

Swept Blend

Combined sweep and loft:

• Profile along path
• Guide at sections

Helix

Spiral path:

• Pitch, turns
• Cone angle option

Variable Section Sweep

Profile varies along path:

• Multiple sections
• Guide curves essential

Thin Wall

Hollow part:

• Default inward offset
• Thickness varies possible

Shell

Hollow interior:

• Faces to remove
• Default thickness

Rib

Structural support:

• Profile → thickness
• Draft for molding

Draft

Taper for mold release:

• Faces to draft
• Pull direction

Hole

Standard cutouts:

• Simple, counterbore, countersink
• Spotface, thread

Fillets and Rounds

Smooth edges:

• Variable radius
• Edge vs. face fillet

Chamfer

Beveled edges:

• Distance or two distances
• Angle and distance

Offset

Duplicate face/edge:

• Distance
• Direction

Mirror

Symmetry:

• Plane selection
• Features or bodies

Pattern

Linear or circular:

• Instances
• Spacing
• Geometry seed

Assembly Design

Bottom-Up Assembly

Create parts, then assemble:

• Standard approach
• Clean geometry

Top-Down Assembly

Design in context:

• Layout first
• Parts reference skeleton

Assembly Constraints

Degrees of Freedom

Each unconstrained part has 6 DOF:

• 3 translation
• 3 rotation

Smart Components

Auto-assemble:

• Define connections
• Apply automatically

Subassemblies

Group related parts:

• Hierarchical
• Simplifies top levels

Design Tables

Excel-driven configs:

• Multiple variations
• Part numbers

Large Assembly Tips

• Simplified parts
• Hide features
• Large design review
• Speedpak

Interference Detection

Check for collisions:

• Static analysis
• Dynamic (motion)

Clearance Analysis

Verify gaps:

• Clearance circles
• Report issues

Bill of Materials (BOM)

Parts list:

• Item number
• Description
• Quantity
• Part number

Auto-BOM

From model:

• Update automatically
• Add custom properties

Design Checks

• Mass properties
• Center of mass
• Moment of inertia

Surface Modeling

B-Spline

Basis spline:

• Control points
• Knot vector

Bezier

Polynomial curve:

• Control points
• Endpoints on curve

NURBS

Non-uniform rational B-spline:

• Weights on points
• Most flexible

Blend Surface

Transition between:

• G1 (tangent)
• G2 (curvature)

Fill Surface

Fill gap:

• Constraints at edges
• Continuity options

Loft Surface

Profile to profile:

• Guide curves
• Start/end constraints

Swept Surface

Profile along path:

• Can twist
• Guide rails

Extend Surface

Continue surface:

• Distance or to point
• Extend type

Offset Surface

Parallel surface:

• Distance
• Both sides

Knit Surface

Join surfaces:

• Create solid
• Fill gaps

Boundary Surface

From boundary edges:

• Complex topology

Style Spline

Smooth through points:

• Handles for control
• Curvature continuous

Rendering and Visualization

PhotoView 360

Realistic rendering:

• Materials
• Lighting
• Environment

Material Assignment

Physical properties:

• Color, texture
• Reflectivity
• Roughness

Lighting

• Ambient
• Directional
• Point
• Spot

Ray Tracing

Photo-realistic:

• Reflections
• Refractions
• Shadows

Animation

Show design:

• Exploded view
• Motion study
• Rendering sequence

Virtual Reality

Immersive review:

• Walk through
• Experience scale

3D PDFs

Portable:

• Embed in PDF
• Annotate

Augmented Reality

On mobile:

• Overlay in reality
• Check fit

Manufacturing Outputs

STEP

Standard exchange:

• Neutral format
• Most complete

IGES

Older standard:

• Geometry only
• May lose features

STL

Stereolithography:

• Triangle mesh
• 3D printing standard

ACIS

SAT format:

• SolidWorks native
• Feature data

Parasolid

XT:

• Neutral solid
• Industry standard

3D PDF

Publish design:

• Embed viewer
• Annotate

DXF/DWG

2D drawings:

• AutoCAD format
• For fabrication

IDF

PCB integration:

• Board outline
• Mount holes

cgr

Lightweight:

• No geometry detail
• Viewing only

Render Image

PNG, JPEG, TIFF:

• Marketing
• Documentation

Animation Video

MP4, AVI:

• Presentations
• Manuals

Simulation Integration

Finite Element Analysis (FEA)

Structural analysis:

• Meshing
• Loads, constraints
• Results visualization

Mesh Types

Mesh Quality

• Aspect ratio
• Jacobian
• Element quality

Loads

• Force
• Pressure
• Gravity
• Thermal

Boundary Conditions

• Fixed
• Displacement
• Roller

Thermal Analysis

Heat transfer:

• Conduction
• Convection
• Radiation

Fluid Flow

CFD:

• Flow paths
• Pressure drop

Modal Analysis

Vibration:

• Natural frequencies
• Mode shapes

Optimization

Improve design:

• Topology
• Shape
• Size

Design Study

Parameters vary:

• What-if analysis
• Optimization

Simulation Types

• Static
• Dynamic
• Fatigue
• Buckling

Design for Manufacturability

Design for Injection Molding

• Draft angles
• Uniform wall thickness
• Radii at corners
• Undercuts need slides

Design for Machining

• Allow for tool access
• Standard drill sizes
• Chamfers for edges

Design for Sheet Metal

• Bend allowances
• K-factor
• Relief cuts

Design for Casting

• Draft
• Uniform sections
• Rounded fillets

Tolerancing

GD&T (Geometric Dimensioning and Tolerancing):

• Position
• Profile
• Flatness
• Perpendicularity

GD&T Symbols

Tolerance Stack Analysis

Cumulative variation:

• Worst case
• Statistical

Cost Optimization

Minimize material:

• Hollow sections
• Shape optimization

Rapid Prototyping

3D printing:

• Orientation
• Supports
• Materials

Parametric Best Practices

Sketch Best Practices

1. Fully constrain
2. Use relations
3. Name dimensions
4. Reuse sketches

Feature Best Practices

1. Draft first
2. Simple features
3. Mirror when possible
4. Use patterns

Assembly Best Practices

1. Use subassemblies
2. Smart components
3. Layout skeleton
4. Top-down where useful

Design Intent

1. Define intent early
2. Use equations
3. Global variables
4. Configuration

Large Assembly Best Practices

1. Speedpak
2. Hide details
3. Load components as needed
4. Defeature for analysis

Performance Tips

• Lightweight components
• Suppress features
• Rebuild only when needed
• Graphics quality

Collaboration

• Design library
• Design tables
• Pack and go
• PDM integration

Version Control

• Revision control
• Backup
• Release process
• ECOs

Standards

• Company standards
• Industry standards
• ISO, ASME Y14.5
• Drawing templates

Documentation

• Title block
• Views
• Dimensions
• Notes

Common Errors to Avoid

• Unconstrained sketches causing issues
• Too many features making rebuild slow
• Not using design intent properly
• Missing draft on molded parts
• Forgetting tolerance stack-up
• Over-constrained models
• Not checking interference
• Saving in wrong format
• Ignoring simulation results
• Not considering manufacturing in design
• Complex lofts causing issues
• Not testing in context

Key References

• SolidWorks Official Training
• Autodesk Inventor Official Training
• Mastering SolidWorks by Parrish
• GD&T Application and Interpretation by Krulikowski