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Technical Sketching. Chapter 3. Objectives. Define vertex, edge, plane, surface, and solid Identify four types of surfaces Identify five regular solids Draw points, lines, angled lines, arcs, circles, and ellipses . Objectives (cont.).
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Technical Sketching Chapter 3
Objectives • Define vertex, edge, plane, surface, and solid • Identify four types of surfaces • Identify five regular solids • Draw points, lines, angled lines, arcs, circles, and ellipses
Objectives (cont.) • Apply techniques that aid in creating legible well-proportioned sketches • Apply techniques to draw irregular curves • Create a single view sketch • Create an oblique sketch • Create a one-point perspective sketch • Create an isometric sketch of an object
Understanding Solid Objects • Three-dimensional figures are referred to as solids • Solids are bounded by the surfaces that contain them • These surfaces can be: • Planar • Single-curved • Double-curved • Warped
Types of Solids • Polyhedra • Solids that are bounded by plane surfaces • These planar surfaces are also referred to as faces of the object • A polygon is a planar area that is enclosed by straight lines
Types of Solids • Regular polyhedra • If the faces of a solid are equal regular polygons it is a regular polyhedron • There are five regular polyhedra: • Tetrahedron • Hexahedron • Octahedron • Dodecahedron • Icosahedron
Types of Solids • Prisms • A prism has two bases which are parallel equal polygons
Types of Solids • Pyramids • A pyramid has a polygon for a base and triangular lateral faces which intersect at a vertex
Types of Solids • Cylinders • A cylinder has a single-curved exterior surface
Types of Solids • Cones • A cone has a single-curved exterior and can be formed by moving one end of a straight line around a circle while keeping the other end fixed at a point
Types of Solids • Sphere • A sphere has a double-curved exterior that can be formed by revolving a circle around one of its diameters • Torus • A torus is shaped like a donut and has a double curved boundary surface
Types of Solids • Ellipsoids • An oblate or prolate ellipsoid is shaped like an egg and can be created by revolving an ellipse around one of its axes
Understanding Sketching Techniques • Analyzing complex objects • The ability to break down complex shapes into simpler geometric primitives is an essential skill for sketching and modeling objects • Basic curves and straight lines are the basis of many objects
Understanding Sketching Techniques • Essential shapes can be blocked in using construction lines
Understanding Sketching Techniques • Contours show the contrast between positive and negative space
Viewpoint • As you sketch, you should maintain a consistent viewpoint • Examine the shapes you see from that viewpoint • Sketch the object as it actually looks, not how you envision it is
Shading • Adding shading to a sketch can give it a more realistic appearance • Hatching lines and stippling are common forms of shading
Edges and Vertices • An edge is formed where two surfaces intersect • Edges are represented by visible or hidden lines • A vertex is formed where three or more surfaces intersect • The end of an edge is a vertex
Points and Lines • A point represents a location in space and has no width, height, or depth • Points in drawings are represented by: • The intersection of two lines • A short crossbar on a line • A small cross • Points are not represented by simple dots
Points and Lines • A line is used in drawings to represent the edge of a solid object • A straight line is the shortest distance between two points • Lines may be parallel or perpendicular to other lines
Angles • An angle is formed by two intersecting lines • There are 360 degrees in a full circle • A degree is divided into 60 minutes • A minute is divided into 60 seconds • Angles may be complementary or supplementary
Drawings and Sketches • The following skills are important for sketches and drawings: • Accuracy • Speed • Legibility • Neatness
Freehand Sketching • Freehand sketches are a helpful way to organize thoughts and record ideas • The degree of precision of a given sketch depends on its use • A freehand sketch should show attention to proportion, clarity, and correct line widths
Line Weights • Make dimension, extension, and centerlines thin, sharp, and black • Make hidden lines medium and black • Make visible and cutting plane lines thick and black • Make construction lines thin and light
Maintaining Proportions • Sketches are not usually made to a specific scale • The most important rule in freehand sketching is to keep the sketch in proportion • Grid paper can help you maintain proportions
One View Drawings • Frequently a single view supplemented by notes and dimensions can describe a simple object
Pictorial Sketching • A pictorial sketch represents a 3D object on a sheet of 2D paper by orienting the object so you can see its width, height, and depth in a single view
Pictorial Sketching • The three common methods used to sketch pictorials are: • Isometric sketching • Oblique sketching • Perspective sketching
Oblique Sketches • In oblique drawing, circles and angles parallel to the projection plane are true size and shape • Three things affect oblique sketches • Which surface is parallel to the projection plane • The angle and orientation for the receding lines depicting depth • The scale chosen for the receding lines
Oblique Sketches • Forty-five degrees is often chosen for the angle of receding lines • Thirty degrees is also a popular choice and can look more realistic • In cavalier projection, receding lines are drawn at full scale • In cabinet projection, the depth is represented at half scale
Perspective Pictorials • Perspective pictorials approximate the view produced by the human eye • Unlike parallel projection, perspective projectors converge at a vanishing point • There are three types of perspective: • One point • Two point • Three point
