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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

- These surfaces can be:

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

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