chp 3 - Fundamentals of Technical Sketching and 3D Modeling

Technical sketching

A rough preliminary drawing representing the main features of a product or structure.

Methods of technical sketching

Freehand, mechanical, and digital (CAD).

Sketch types for audiences

Personal: Freehand sketches; Technical: Multiview sketches; Non-technical: Pictorial sketches.

Contour sketch

A sketch that outlines the shape of an object.

Negative space sketching

Sketching the space around the object (negative space) rather than the object itself.

Starting a contour sketch

By slowly tracing the outline of the object with your eyes and moving your pencil across the paper.

Upside-down sketching

A technique where you turn a recognizable object upside-down to focus on its shape.

Construction lines in sketching

To guide the overall shape and proportions of a sketch.

Proportions in sketching

The ratio between any two dimensions of an object.

Basic geometric elements

Points, lines, circles, and arcs.

Implicit constraint in CAD

A constraint automatically inferred by the software based on how the sketch was drawn.

Explicit constraint

A constraint applied manually by the user to a sketch.

Dimensions in constraint-based modeling

To define the size and location of entities.

References in CAD sketching

Existing features like datums or axes that can be referenced when constructing new features.

Relation in CAD modeling

A mathematical or geometric relationship between dimensions or entities.

Origin in a coordinate system

The reference point from which all positions are measured (0,0,0).

Right-hand rule in coordinate systems

A method to determine the orientation of axes in a 3D space.

Absolute coordinates

Coordinates referenced to the origin (0,0,0).

Relative coordinates

Coordinates referenced from a previously defined point.

World vs local coordinate systems

The world coordinate system is fixed, while the local system can be moved and rotated.

Tangent in geometry

A condition where a line touches a curve at only one point.

Plane in geometric terms

A flat, two-dimensional surface that contains every straight line between points on it.

Conic curves

Curves such as parabolas, ellipses, and hyperbolas derived from cutting a cone.

Spline curve

A smooth, freeform curve connecting a series of control points.

Bezier curve

A curve that uses control points to approximate a shape, with the first and last points on the curve. in a Bézier curve, the effect is not localized, but globalized. (whole curve shifts)

B-spline curve

A curve that approximates a set of control points with localized control over its shape. Localized effect- around the changed point is where the curve shifts.

Types of quadrilaterals

Square, rectangle, rhombus, and trapezoid.

Sum of angles in a quadrilateral

360 degrees.

Surface in geometry

The outer face of an object bounded by an identifiable perimeter.

Ruled surface

A surface created by moving a straight line along a path.

Developable surface

A surface that can be unfolded onto a plane without distortion.

Freeform surface

A surface that follows no set pattern and requires complex mathematics to define.

Wireframe modeling

The simplest form of 3D modeling, representing objects with edges and vertices.

Issues with wireframe models

Lack of uniqueness and ambiguity.

Surface modeling

A method of defining the surfaces and edges of objects.

Lofting in surface modeling

Creating surfaces by defining multiple intermediate points along a path.

Boolean operation in 3D modeling

Operations such as union, difference, and intersection used to combine or modify shapes.

Generalized sweep in 3D modeling

Moving a 2D profile along a path to create a 3D object.

Feature duplication in 3D modeling

To replicate features for symmetrical or repetitive model elements.

Significance of feature order in 3D modeling

The order in which features are created affects the final geometry and editing process.

Construction geometry in 3D modeling

Geometry used as a reference to assist in the creation of features, but not part of the final model.

Role of planning in constraint-based modeling

Planning helps ensure that changes to one part of the model adjust other related parts automatically.

Difference between a plane and a surface

A plane is a flat 2D surface, while a surface can be curved and have complex geometry.

Multiview drawing

A drawing that shows different views (top, front, side) of a 3D object.

Coordinate space in engineering design

It provides a reference for locating and constructing geometric forms in CAD systems.

Feature constraints

Constraints control how geometric features behave in relation to one another.

Hyperbola

A hyperbola is a type of conic curve used in designs such as satellite dish reflectors.

Parabola

A parabola is a conic curve often used in antenna designs to focus signals.

Polar coordinates

To define points in a circular coordinate system, using radius and angle.

Cylindrical coordinates

A 3D coordinate system using radius, angle, and height to define points.

Simplification of 3D models

By reducing polygon counts or creating level-of-detail (LOD) models.

Elements defining a view of a 3D model

Camera position, lighting, projection type, and background.

Perspective projection

A method of projection where lines converge to a point, creating depth.

Parallel projection

A projection where all lines remain parallel, without depth, often used in technical drawings.

Multiview sketches

Sketches that show the front, top, and side views of an object.

Shaded sketches

To provide more clarity by showing light and shadow on the object.

Cylinder

A single-curved surface generated by revolving a rectangle around an axis.

Freeform curves

To create complex shapes like car bodies or ergonomic designs.

Feature editing in CAD

Modifying existing features to update the design without starting from scratch.

Auxiliary views in CAD

To show features that are not clearly visible in standard views.

Construction lines

Light lines used to guide the proportions and alignment of a sketch.

Proportioned sketch

A sketch where the dimensions of different features are accurately related to one another.

Estimating dimensions for large objects

Stand at a distance, align a pencil with the object, and transfer the pencil's length to the sketch.

Implicit constraint

A constraint automatically inferred by the software when you draw a feature.

Negative space in sketching

The empty space around the object being drawn.

Points in geometry

Exact locations in space, typically marked as small crosses in technical drawings.

Lines in geometry

Geometric elements with length and direction but no thickness.

Tangent

A line that touches a curve at only one point without crossing it.

Key elements of a circle

Center, radius, and circumference.

Lofting in 3D modeling

A method of creating complex shapes by interpolating between different cross-sections.

Boolean operations in 3D modeling

Operations like union, difference, and intersection used to combine or modify 3D objects.

Feature in CAD modeling

A specific element of a model, such as a hole, cut, or extrusion.

Significance of feature order in CAD

The order in which features are created can affect how they interact with one another.

Feature duplication

Repeating or copying a feature to create symmetrical or repetitive elements in the model.

Profile in 3D modeling

A 2D shape that serves as the base for a 3D feature when extruded or revolved.

Sweep in 3D modeling

A technique where a 2D profile is moved along a path to create a 3D shape.

Role of constraints in 3D modeling

Constraints ensure that features behave predictably when modified.

Construction geometry

Temporary lines, points, or shapes used to aid the creation of other features but not part of the final model.

Freeform modeling

A technique used to create complex, organic shapes not constrained by strict geometric rules.

Right-hand rule

A method used to determine the orientation of axes in a 3D space, where the thumb, index, and middle fingers represent the X, Y, and Z axes, respectively.