## Overview - Parametric modeling is a method of creating 3D digital objects by drawing precise 2D sketches and then converting them into solid geometry using feature commands - The process is **parametric**, meaning dimensions and relationships are stored as editable parameters — changing one value automatically updates all dependent geometry - The complete design workflow spans three interconnected file types: individual solid components, assembled mechanisms, and technical manufacturing documents --- ## Key Concepts - **Part** – a single 3D solid component; the foundational building block of all parametric models - **Assembly** – a collection of individual parts constrained together to simulate a real-world mechanism or structure - **Drawing** – a 2D technical document generated from a part or assembly, used for manufacturing communication - **Feature** – a single modelling operation applied sequentially to build or modify a part's shape - **Sketch** – a 2D profile drawn on a flat plane that serves as the input geometry for sketched features - **Geometric Relation** – a logical constraint applied between sketch entities to control shape behaviour - **Dimension** – a numeric value assigned to sketch geometry to define its exact size or position - **Parametric Link** – an automatic association between geometry elements that ensures changes propagate throughout the model --- ## Detailed Notes ### File Types and Their Roles - **Parts** are always created first — they are the base-level files in any parametric modelling project - **Assemblies** reference multiple part files and position them relative to one another using constraints (e.g., aligning holes, mating flat faces) - **Drawings** are derived views — they pull geometry directly from parts or assemblies and present it in standard engineering projection formats - The three file types form a **linked ecosystem**: editing a part automatically updates every assembly and drawing that references it ### Features: The Building Blocks of a Part - A part is constructed by stacking a sequence of **Features** in order; each feature builds on or modifies the result of the previous one - Features are divided into two categories: | Feature Type | Description | Example | |---|---|---| | **Sketched Feature** | Requires a 2D profile to be drawn first; converts that profile into 3D geometry | Extruding a rectangle into a block | | **Applied Feature** | Modifies existing 3D geometry directly without needing a new 2D profile | Hollowing out a solid body, rounding edges | - The order of features matters — the **feature tree** records every operation chronologically and can be edited or reordered ### Working Modes - Parametric CAD systems operate in two distinct environments that the user alternates between: - **3D Space (Part Mode):** the default environment for viewing the model, selecting reference planes, and applying features to existing geometry - **2D Environment (Sketch Mode):** a flat workspace activated on a specific plane or face, used exclusively for drawing profiles - You must **enter** Sketch Mode to draw, and **exit** Sketch Mode before applying a 3D feature ```mermaid flowchart TD A[Create New Part File] --> B[Select a Plane or Flat Face] B --> C[Enter Sketch Mode] C --> D[Draw 2D Profile] D --> E[Exit Sketch Mode] E --> F[Apply 3D Feature to Profile] F --> G{More Features Needed?} G -- Yes --> B G -- No --> H[Part Complete] ``` --- ### 2D Sketching Entities - Profiles are constructed using basic geometric shapes - Two types of sketch geometry exist: - **Standard geometry** – forms the actual boundary of the future 3D solid - **Construction geometry** – acts as scaffolding for alignment and reference; completely ignored during 3D feature generation #### Lines - **Standard Line** – creates solid boundaries that define the profile shape - **Centerline (Construction Line)** – used purely for reference, symmetry axes, or as a revolve axis; does not generate 3D mass #### Rectangles | Rectangle Type | How It Is Drawn | Best Use Case | |---|---|---| | **Corner Rectangle** | Defined by two diagonally opposite corner points | General-purpose rectangular profiles | | **Center Rectangle** | Drawn outward from a central origin point | Symmetric geometry centred on the origin | | **3-Point / Parallelogram** | Defined by three points allowing angled sides | Shapes that do not align with standard axes | #### Circles and Arcs - **Centerpoint Circle** – defined by clicking a centre point and dragging outward to set the radius - **Centerpoint Arc** – similar to a circle but requires start and end points to define the sweep angle - **Tangent Arc** – must originate from an existing endpoint; automatically creates a smooth, flowing transition from the previous line or arc without any sharp corner --- ### Controlling the Sketch: Relations and Dimensions - A sketch must be **fully defined** (every point locked in position and size) to behave predictably during 3D operations - Full definition is achieved through two mechanisms: 1. **Geometric Relations** – lock the shape logic 2. **Dimensions** – lock the exact size #### Geometric Relations (Constraints) | Relation | Function | Common Use Case | |---|---|---| | **Horizontal / Vertical** | Locks a line precisely to the X or Y axis | Ensuring a base edge is perfectly flat | | **Collinear** | Forces two separate lines onto the same infinite path | Aligning disconnected edges | | **Perpendicular** | Forces two lines to meet at exactly 90° | Creating square corners | | **Parallel** | Ensures two lines travel in the same direction at equal distance | Drawing consistent slots or channels | | **Tangent** | Creates a smooth, continuous transition between a line and an arc, or two arcs | Designing organic, flowing contours | | **Coincident** | Snaps a point precisely onto another point, line, or curve | Closing gaps to complete a profile | | **Concentric** | Forces two arcs or circles to share the same centre point | Designing uniform tubes or pipes | #### Dimensions - **Linear Dimension** – controls the distance between two points or the length of a line - **Angular Dimension** – controls the degree angle between two non-parallel lines - **Radial / Diametric Dimension** – controls the size of arcs and circles #### Recommended Workflow for Sketch Definition ```mermaid flowchart LR A[Draw Rough Shape] --> B[Apply Geometric Relations] B --> C[Add Dimensions] C --> D[Fully Defined Sketch] ``` - **Step 1:** Sketch the approximate shape freely - **Step 2:** Apply relations to lock in geometric logic (parallel, tangent, coincident, etc.) - **Step 3:** Add dimensions to assign precise numeric values - Result: a **fully defined** sketch with no remaining degrees of freedom --- ### Advanced Sketching Workflows #### Dynamic Sketch Planes - Sketches do not have to start from the default reference planes (Top, Front, Right) - Any **flat, planar face** on an existing 3D body can be selected as a new sketch plane - **Limitation:** standard 2D sketching cannot be performed directly on curved or cylindrical surfaces #### Projecting Geometry - When building new features on top of existing 3D geometry, you can extract existing edges into the current sketch - **Function:** projects (copies) the outline of an existing 3D face or edge flat onto the active 2D sketch plane - **Parametric Linking:** projected geometry maintains a live link to the source 3D body — if the original body changes size, the projected sketch lines update automatically - This technique ensures new features remain aligned and proportional to existing geometry without manual re-measurement --- ### 3D Feature Generation #### Linear Extrusion - Pushes a flat 2D profile straight outward along an axis perpendicular to the sketch plane, adding material | Extrusion Type | Behaviour | |---|---| | **Blind** | Extrudes a specific, user-defined numeric distance | | **Mid-Plane** | Extrudes equally in both directions from the sketch plane (e.g., 10 units total = 5 forward + 5 backward) | | **Up to Surface** | Extrudes until the new material meets an existing face on the model | #### Revolve - Sweeps a 2D profile around a central axis to generate cylindrical, spherical, or toroidal shapes **Requirements:** - A **closed 2D profile** (the cross-section shape) - A **distinct straight line** acting as the axis of revolution (typically a centreline) **Rules:** - The 2D profile **must not cross** the axis line — otherwise the generated solid would self-intersect - The sweep angle can be a full **360°** or any **partial angle** ```mermaid flowchart LR A[Draw Closed Profile] --> B[Draw Centreline Axis] B --> C[Select Revolve Command] C --> D[Set Sweep Angle] D --> E[Cylindrical / Toroidal Solid Generated] ``` #### The Shell Command (Applied Feature) - An applied feature that hollows out a solid 3D body, leaving behind thin, uniform walls - **Workflow:** 1. Select the solid body to hollow 2. Specify the desired **wall thickness** 3. Select the face(s) to be completely **removed** (these become the openings) - **Multi-Thickness Option:** advanced settings allow specific walls within the same part to have different thicknesses where required - No new 2D sketch is needed — the shell command operates directly on existing 3D geometry ```mermaid flowchart TD A[Solid 3D Body] --> B[Select Shell Command] B --> C[Specify Wall Thickness] C --> D[Select Face to Remove as Opening] D --> E[Hollow Body with Uniform Walls] ``` --- ## Key Terms - **Parametric Modeling** – a CAD methodology where geometry is driven by editable parameters and relationships, enabling automatic updates when values change - **Part** – a single solid component file; the foundational unit of a parametric model - **Assembly** – a file that combines multiple parts using positional constraints to simulate a mechanism - **Drawing** – a 2D technical document derived from a part or assembly for manufacturing communication - **Feature** – a single modelling operation (sketched or applied) that contributes to a part's final shape - **Feature Tree** – the chronological record of all features applied to a part, editable and reorderable - **Sketch Mode** – a dedicated 2D drawing environment activated on a plane or flat face - **Centreline** – a construction line used for symmetry reference or as a revolve axis; does not create 3D geometry - **Geometric Relation** – a constraint that defines a logical rule between sketch entities (e.g., parallel, tangent, coincident) - **Fully Defined Sketch** – a sketch where every point is locked in position and size with zero remaining degrees of freedom - **Extrusion** – a feature that pushes a 2D profile linearly into the third dimension to add material - **Revolve** – a feature that sweeps a 2D profile around an axis to generate rotational geometry - **Shell** – an applied feature that hollows a solid body by removing selected faces and leaving walls of specified thickness - **Projected Geometry** – existing 3D edges copied onto a 2D sketch plane, maintaining a parametric link to the source body - **Tangent Arc** – an arc that originates from an existing endpoint and automatically maintains a smooth transition with no sharp corner --- ## Quick Revision - **Parts** are the foundational files — they are built by stacking sequential **features** in a recorded feature tree - **Sketched features** require a 2D profile drawn in Sketch Mode; **applied features** (e.g., shell) modify existing 3D geometry directly - The system alternates between **3D Part Mode** (viewing and applying features) and **2D Sketch Mode** (drawing profiles) - **Centrelines** are construction geometry — they serve as reference axes and symmetry guides but never generate 3D mass - **Geometric relations** control shape logic (parallel, tangent, perpendicular); **dimensions** control absolute numeric size - A sketch must be **fully defined** (zero degrees of freedom) before reliably generating 3D features - **Extrusion** pushes a profile linearly; **revolve** sweeps a profile around an axis to create rotational solids - **Projected geometry** copies existing 3D edges into a new sketch, maintaining a live parametric link - The **shell** command hollows solid bodies by specifying wall thickness and selecting faces to remove as openings - Any **flat face** on existing geometry can serve as a sketch plane, but **curved surfaces** cannot be sketched on directly