# Technical Sketching - PowerPoint PPT Presentation

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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

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

• 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

### 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