2.3 Precision input and constraints

Precision input and constraints are crucial for creating accurate CAD designs. They allow you to input exact dimensions and establish relationships between objects. This ensures your drawings are precise and maintain their intended structure when modified.

Geometric and dimensional constraints define how objects interact and maintain their size. By using these tools, you can create parametric models that update automatically when changes are made. This saves time and reduces errors in your designs.

Precise Dimensions via Keyboard

Inputting Exact Values

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• Enter precise dimensions using the keyboard to specify exact lengths, angles, or coordinates when creating or modifying objects
• Override the default dimensions determined by cursor position or mouse click by inputting specific numeric values
• Use keyboard input in conjunction with various drawing and editing tools (lines, circles, rectangles)
• Finalize the input and apply the specified dimension to the object being created or modified by pressing the Enter or Return key after typing the desired value
• Support the use of different units of measurement (inches, millimeters, centimeters) depending on the software's settings or user preferences

Relative and Coordinate Dimensions

• Enter relative dimensions using arithmetic operators (+, -, *, /) to specify dimensions in relation to existing objects or reference points
• Input polar coordinates (distance and angle) via the keyboard to precisely position objects in 2D space
• Use Cartesian coordinates (X, Y, and Z values) to accurately place objects in 3D space
• Combine relative and absolute dimensions to create complex shapes and designs
• Utilize keyboard input for precise positioning in move or copy commands

Geometric Constraints for Relationships

Types of Geometric Constraints

• Define relationships between objects using geometric constraints (perpendicularity, parallelism, tangency, concentricity, coincidence)
• Ensure two lines, edges, or faces are at a 90-degree angle to each other with the perpendicular constraint
• Maintain a constant distance and orientation between two lines, edges, or faces using the parallel constraint
• Create a point of contact between a line and a curve or between two curves (circle and a line, two circles) with the tangent constraint
• Position two or more circular or curved objects to share the same center point using the concentric constraint
• Align two points to occupy the same position in space with the coincident constraint

Applying and Modifying Constraints

• Apply geometric constraints automatically based on user actions or manually by selecting objects and choosing the appropriate constraint type
• Add, modify, or remove constraints as needed to update relationships between objects and maintain design intent
• Promote the creation of parametric models by using geometric constraints, allowing for easier modifications and updates to the design
• Combine multiple constraints to create complex relationships between objects
• Visualize and manage applied constraints using the software's constraint management tools

Dimensional Constraints for Sizes

Types of Dimensional Constraints

• Specify and control object sizes using dimensional constraints (lengths, diameters, radii, angles)
• Constrain the distance between two points, edges, or faces, ensuring the specified length is maintained with linear dimensions
• Control the size of circular features (holes, cylindrical objects) using radial and diametric dimensions
• Maintain the specified angle value between two lines, edges, or faces with angular dimensions
• Apply dimensional constraints to arcs and curves to control their size and shape

Applying and Editing Dimensional Constraints

• Apply dimensional constraints by selecting objects and specifying the desired dimension value using the keyboard or dimensioning tools
• Display constrained dimensions as annotated values on the object, clearly indicating the controlled sizes
• Automatically update the size of associated objects while maintaining relationships defined by other constraints when editing a constrained dimension value
• Ensure objects are created and maintained at intended sizes, reducing errors and facilitating design changes
• Use dimensional constraints in combination with geometric constraints to create fully defined parametric models

Parametric Relationships Between Objects

Creating Parametric Dependencies

• Define dependencies between objects using parametric relationships, allowing changes made to one object to automatically propagate to related objects
• Create a hierarchy of parent-child relationships, where the properties of child objects are dependent on the properties of their parent objects
• Assign parameters (dimensions, constraints) to objects to control their sizes, positions, or other properties
• Use expressions or formulas to define relationships between parameters, enabling the creation of complex, interrelated designs
• Automatically update all related objects based on defined parametric relationships when a parameter is modified

Benefits and Applications

• Enable quick and efficient design iterations by modifying a single parameter and having the entire model update accordingly
• Promote design flexibility by exploring different design variations and optimizing models based on specific requirements or constraints
• Establish parametric relationships through the use of geometric and dimensional constraints, as well as by linking dimensions or properties between objects
• Apply parametric modeling in various fields (mechanical engineering, architecture, product design) to create adaptable and reusable designs
• Streamline the design process by automating repetitive tasks and reducing manual editing efforts