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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

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Technical sketching l.jpg

Technical Sketching

Chapter 3

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  • 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

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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

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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

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Understanding Solid Objects

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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

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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

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Types of Solids

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Types of Solids

  • Prisms

    • A prism has two bases which are parallel equal polygons

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Types of Solids

  • Pyramids

    • A pyramid has a polygon for a base and triangular lateral faces which intersect at a vertex

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Types of Solids

  • Cylinders

    • A cylinder has a single-curved exterior surface

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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

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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

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Types of Solids

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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

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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

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Understanding Sketching Techniques

  • Essential shapes can be blocked in using construction lines

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Understanding Sketching Techniques

  • Contours show the contrast between positive and negative space

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  • 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

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  • Adding shading to a sketch can give it a more realistic appearance

    • Hatching lines and stippling are common forms of shading

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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

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Edges and Vertices

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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

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Points and Lines

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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

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Points and Lines

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  • 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

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Drawings and Sketches

  • The following skills are important for sketches and drawings:

    • Accuracy

    • Speed

    • Legibility

    • Neatness

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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

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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

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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

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One View Drawings

  • Frequently a single view supplemented by notes and dimensions can describe a simple object

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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

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Pictorial Sketching

  • The three common methods used to sketch pictorials are:

    • Isometric sketching

    • Oblique sketching

    • Perspective sketching

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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

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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

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Oblique Sketches

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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

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