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Technical Sketching

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# Technical Sketching - PowerPoint PPT Presentation

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