Everything we use has symbols and legends for us to follow. But we would never know what the symbols meant unless we had a Legend. Everything we use has symbols and legends for us to follow. But we would never know what the symbols meant unless we had a Legend. Drawings use graphics to communicate. Drawings use graphics to communicate. Writing is a form of graphic communication. Writing is a form of graphic communication. Technical drawing is also graphic communication specific to technology. Technical drawing is also graphic communication specific to technology. Most common types: engineering drawings and diagrams.Most common types: engineering drawings and diagrams. The Technological World Chapter 11:Communicating with Symbols

Diagram of pliers Technology: is a set of techniques used by humans to design, build and maintain objects and systems that we want or need. Technology: is a set of techniques used by humans to design, build and maintain objects and systems that we want or need. Engineering drawing of pliers

2 Lines and Geometry in Technical Drawings Before a technical object can be manufactured, its shape and dimensions must be determined. A technical drawing must be created. Before a technical object can be manufactured, its shape and dimensions must be determined. A technical drawing must be created. Technical drawings can be made by hand or on a computer. Technical drawings can be made by hand or on a computer. Technical Drawings: are used in technology to communicate information about an object or a system. Technical Drawings: are used in technology to communicate information about an object or a system. EST AST

Basic and Geometric Lines Basic Lines: used in drafting are lines whose appearance and meaning are determined by international agreements. Thick lines Medium lines Fine lines

Hidden Lines – represent features that cannot be seen in the current view. They are as dark as the object lines. Center lines – represent symmetry and mark the center of circles, the axes of cylinders, and the axes of symmetrical parts, such as bolts Object/Visible Lines – represent visible features for an object. They are the darkest and most present. Types of Lines in Orthographic Projections Construction lines - Basic faint lines which are drawn to provide a framework for the completion of the projection. Dimension Lines display precise information about the size of the object. 10cm Section/Cutting Plane Lines Are used to represent where the object is to be “cut” or sectioned to reveal interior details. This is used when other views may not adequately reveal information about the object. A A

Construction Lines Construction lines When a drawing is rendered, basic faint lines are drawn to provide a framework for the completion of the projection. Although not part of the object, these lines provide the framework to construct the drawing of the object.

Height Depth Width Front View Top View Right Side View Dimension Lines Dimension Lines display precise information about the size of the object.

Height Depth Width Front View Top View Right Side View Front View Top View Right Side View Object/Visible Lines Object Lines Represent features that are only visible in the current view. Extension Line Dimension Line

Hidden lines Front View Top View Right Side View ALL Hidden or internal details must be included. What does the inside of this block look like? represent features that cannot be seen in the current view. We show these unseen details, with dashed lines.

Center Lines Front View Top View Right Side View represent symmetry and mark the center of circles, the axes of cylinders, and the axes of symmetrical parts, such as bolts. Again, though not part of the object, these lines are important elements of the objects dimension and construction.

Sectioning of a view A A A A Section Lines Are used to represent where the object is to be “cut” or sectioned to reveal interior details. This is used when other views may not adequately reveal information about the object. Sectional view A:A The section line labeled A:A shows the arrows pointing in the direction to which you are observing the “cut” or section.

Geometric Lines Are figures that are composed according to the rules of geometry, the art of drafting lines and curves with a ruler and a compass. Are figures that are composed according to the rules of geometry, the art of drafting lines and curves with a ruler and a compass. Geometric rules and tools allow for: Geometric rules and tools allow for: Horizontal, straight, parallel lines.Horizontal, straight, parallel lines. Vertical, straight, parallel lines that are perpendicular to the horizontal lines.Vertical, straight, parallel lines that are perpendicular to the horizontal lines. Oblique lines.Oblique lines. Circles and Ellipses with defined radii.Circles and Ellipses with defined radii.

2.3 Three Ways of Producing Technical Drawings Freehand: Sketch Freehand: Sketch Drawing with drafting tools (manual drafting instruments) Drawing with drafting tools (manual drafting instruments) Using drafting software: computer- aided drawing (CAD) Using drafting software: computer- aided drawing (CAD)

Sketch, Drafting, & CADs Sketch: Quick illustration of an object that is drawn freehand, respecting, as much as possible, the conventions of drafting. Sketch: Quick illustration of an object that is drawn freehand, respecting, as much as possible, the conventions of drafting. 1 st drawings of an object are sketches. 1 st drawings of an object are sketches. 2 nd would be the manual drafting instruments’ drawings or CADs. 2 nd would be the manual drafting instruments’ drawings or CADs. Drawings with Manual Drafting Instruments: used to create very precise technical drawings prior to CADs. Drawings with Manual Drafting Instruments: used to create very precise technical drawings prior to CADs.

3 Projections A projection is the representation of a three-dimensional object on a two- dimensional surface. A projection is the representation of a three-dimensional object on a two- dimensional surface. To understand these drawings, we must be able to recognize and analyze different projections. To understand these drawings, we must be able to recognize and analyze different projections. Space tech. terminology pg. 343Space tech. terminology pg. 343 Projections differ by two aspects: Projections differ by two aspects: Position of object with respect to paper.Position of object with respect to paper. Angle between the visual rays and paper.Angle between the visual rays and paper. Three of the most commonly used projections are: Three of the most commonly used projections are: 1.Multiview 2.Isometric 3.Oblique EST AST

An Orthogonal Projection is a projection in which all of the visual rays from the object are perpendicular to the surface of a sheet of paper. An Orthogonal Projection is a projection in which all of the visual rays from the object are perpendicular to the surface of a sheet of paper. Projections Orthogonal projections Multiview projections Isometric projections Oblique projections 1 2 3

3.1 Multiview Projections In a multiview projection, each face of the object is drawn separately looking at it from straight on. 2D In a multiview projection, each face of the object is drawn separately looking at it from straight on. 2D 6 views: 6 views: FrontFront RearRear left-sideleft-side right-sideright-side TopTop Bottom.Bottom. EST AST

Multiview Projections  Usually only the top, front and right side of the object are illustrated; presented in an L-shape.  One side of object is always parallel to the paper. All measurements and angles present.

Each view is constructed so that information (dimensions, and object edges, etc..), are clearly related to the other views. Conventional Orthographic Views Height Depth Width Front View Top View Right Side View Front View Top View Right Side View

3.2 Isometric Projections Is a form of perspective drawing in 3D. Is a form of perspective drawing in 3D. Perspective Drawing represents the three dimensions of an object in the same view. Perspective Drawing represents the three dimensions of an object in the same view. An isometric projection is a perspective drawing of an object where the principal edges are arranged on three isometric axes (120° each). An isometric projection is a perspective drawing of an object where the principal edges are arranged on three isometric axes (120° each). EST AST No surface of the object is parallel to the paper, measurements parallel to isometric axes are to scale, angles are not. No surface of the object is parallel to the paper, measurements parallel to isometric axes are to scale, angles are not.

Isometric Drafting

3.3 Oblique Projections Is a perspective drawing in 3D. Is a perspective drawing in 3D. An oblique projection is a perspective drawing in which one of the object’s sides is parallel to the sheet of paper, but its depth is represented by parallel straight lines drawn at an oblique angle. An oblique projection is a perspective drawing in which one of the object’s sides is parallel to the sheet of paper, but its depth is represented by parallel straight lines drawn at an oblique angle. Produce drawings with precise measurements for two dimensions: height and length. Produce drawings with precise measurements for two dimensions: height and length. EST AST

Oblique Projections

The Use of Projections in Engineering Drawings Multiple projections are combined in the engineering drawings for a project. Multiple projections are combined in the engineering drawings for a project. Most commonly used are: Most commonly used are: General drawingsGeneral drawings Axonometric Projections: Exploded view drawingsAxonometric Projections: Exploded view drawings Detail drawingsDetail drawings

General Drawing: an engineering drawing, shows overall design. Multiview or isometric. General Drawing: an engineering drawing, shows overall design. Multiview or isometric. Axonometric Projection: parallel projection used to create a 3D drawing, where the object is rotated along one or more of its axes relative to the plane of projection. Axonometric Projection: parallel projection used to create a 3D drawing, where the object is rotated along one or more of its axes relative to the plane of projection.parallel projectionparallel projection Exploded View Drawing: is an engineering drawing that shows the different parts, or features, of the object separately. Usually multiview and isometric projections. Bill of materials: includes name of each part, quantity, and the materials needed for construction.Exploded View Drawing: is an engineering drawing that shows the different parts, or features, of the object separately. Usually multiview and isometric projections. Bill of materials: includes name of each part, quantity, and the materials needed for construction. Detail Drawing: is an engineering drawing, specifies the details needed to make a part of an object. Usually a multiview projection. Includes size, position and diameter of holes. Detail Drawing: is an engineering drawing, specifies the details needed to make a part of an object. Usually a multiview projection. Includes size, position and diameter of holes.

EST AST General Drawing

Exploded View

Detail Drawing

4. Engineering Drawing Scale: is used to reduce or enlarge the representation of an object on a sheet of paper. This is called drawing to scale. Scale: is used to reduce or enlarge the representation of an object on a sheet of paper. This is called drawing to scale. Scale reduction: reduce all measurements of an object by the same factor. 1:50 make measurements 50 times smaller. Scale reduction: reduce all measurements of an object by the same factor. 1:50 make measurements 50 times smaller. Scale increase: increase all measurements of an object by the same factor. 20:1 make measurements 20 times bigger. Scale increase: increase all measurements of an object by the same factor. 20:1 make measurements 20 times bigger. Full-size: object represented with its real measurements. 1:1 make the measurements exactly the same size. Full-size: object represented with its real measurements. 1:1 make the measurements exactly the same size. Drawing’s title block includes: name of draftsperson, title of drawing, date when made, and scale that was used. Drawing’s title block includes: name of draftsperson, title of drawing, date when made, and scale that was used.

Scale of 1:2

Dimensional Tolerances Since machines, tools, instruments, and the operators of machines are not perfect, the manufactured parts may be slightly different from the dimensions indicated on the drawing. Since machines, tools, instruments, and the operators of machines are not perfect, the manufactured parts may be slightly different from the dimensions indicated on the drawing. A dimensional tolerance is an indicator of the maximum acceptable difference between a specified measurement and the actual measurement on the finished object. A dimensional tolerance is an indicator of the maximum acceptable difference between a specified measurement and the actual measurement on the finished object. EST AST

Tolerance If the tolerance value applies to the entire drawing then its written in the title block. If the tolerance value applies to the entire drawing then its written in the title block.

Dimensioning Refers to the process of indicating the real dimensions of an object as well as the position of various elements of the object. Refers to the process of indicating the real dimensions of an object as well as the position of various elements of the object. Use dimension lines and extension lines with symbols. Ex: Ø – diameter of holeUse dimension lines and extension lines with symbols. Ex: Ø – diameter of hole R – radius of circle or curve R – radius of circle or curve - degrees of an angle - degrees of an angle

Cross Sections and Sections Cross section: reveals the interior of an object, exposing its hidden details to view. Cross section: reveals the interior of an object, exposing its hidden details to view. 1 st step: select dimension to imaginarily cut to produce cross-sectional view. 1 st step: select dimension to imaginarily cut to produce cross-sectional view. For multiview projection use cutting plane lineFor multiview projection use cutting plane line 2 nd step: draw cross-sectional view indicated by the arrows of the cutting plane line. Surface “cut” represented by hatched lines and hidden lines not used. 2 nd step: draw cross-sectional view indicated by the arrows of the cutting plane line. Surface “cut” represented by hatched lines and hidden lines not used. Section: represents a surface in a cross- sectional view. Section: represents a surface in a cross- sectional view.

Aligned/Revolved Section: is drawn directly on the object represented Aligned/Revolved Section: is drawn directly on the object represented Offset/Removed Section: is drawn outside of the object represented. It is used when adding a revolved section might overload the drawing and make it harder to understand. Offset/Removed Section: is drawn outside of the object represented. It is used when adding a revolved section might overload the drawing and make it harder to understand.

Diagrams A simplified representation of an object, a part of an object or a system. A simplified representation of an object, a part of an object or a system.

Symbols Used in Diagrams

Common Types of Diagrams Using appropriate symbols Refer to diagrams of pliers

Circuit Diagram