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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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PowerPoint Slideshow about 'Technical Sketching' - davida

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Technical Sketching

Chapter 3

• 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

• 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

• 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

• 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

• 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

• Prisms

• A prism has two bases which are parallel equal polygons

• Pyramids

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

• Cylinders

• A cylinder has a single-curved exterior surface

• 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

• 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

• Ellipsoids

• An oblate or prolate ellipsoid is shaped like an egg and can be created by revolving an ellipse around one of its axes

• 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

• Essential shapes can be blocked in using construction lines

• Contours show the contrast between positive and negative space

• 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

• 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

• 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

• 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

• 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

• The following skills are important for sketches and drawings:

• Accuracy

• Speed

• Legibility

• Neatness

• 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

• 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

• Sketches are not usually made to a specific scale

• The most important rule in freehand sketching is to keep the sketch in proportion

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

• 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

• The three common methods used to sketch pictorials are:

• Isometric sketching

• Oblique sketching

• Perspective sketching

• 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

• 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 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