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.

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The Technological World Chapter 11Communicating
with Symbols

• 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.
• Writing is a form of graphic communication.
• Technical drawing is also graphic communication
  specific to technology.
• Most common types engineering drawings and
  diagrams.

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Diagram of pliers
Engineering drawing of pliers

• Technology is a set of techniques used by humans
  to design, build and maintain objects and systems
  that we want or need.

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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.
• 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.

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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

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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.
Object/Visible Lines represent visible features
for an object. They are the darkest and most
present.
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
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.
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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.
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Dimension Lines
Dimension Lines display precise information
about the size of the object.
Top View
Right Side View
Front View
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Object/Visible Lines
Object Lines Represent features that are only
visible in the current view.
Extension Line
Top View
Right Side View
Dimension Line
Top View
Front View
Right Side View
Front View
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Hidden lines

• represent features that cannot be seen in the
  current view. We show these unseen details, with
  dashed lines.

ALL Hidden or internal details must be
included.What does the inside of this block
look like?
Top View
Right Side View
Front View
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Center Lines

• represent symmetry and mark the center of
  circles, the axes of cylinders, and the axes of
  symmetrical parts, such as bolts.

Top View
Again, though not part of the object, these lines
are important elements of the objects dimension
and construction.
Right Side View
Front View
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Sectioning of a view
The section line labeled AA shows the arrows
pointing in the direction to which you are
observing the cut or section.
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 AA
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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.
• Geometric rules and tools allow for
• Horizontal, straight, parallel lines.
• Vertical, straight, parallel lines that are
  perpendicular to the horizontal lines.
• Oblique lines.
• Circles and Ellipses with defined radii.

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2.3 Three Ways of Producing Technical Drawings

• Freehand Sketch
• Drawing with drafting tools (manual drafting
  instruments)
• Using drafting software computer-aided drawing
  (CAD)

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Sketch, Drafting, CADs

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

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3 Projections

• 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.
• Space tech. terminology pg. 343
• Projections differ by two aspects
• Position of object with respect to paper.
• Angle between the visual rays and paper.
• Three of the most commonly used projections are
• Multiview
• Isometric
• Oblique

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• 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.

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3.1 Multiview Projections

• In a multiview projection, each face of the
  object is drawn separately looking at it from
  straight on. 2D
• 6 views
• Front
• Rear
• left-side
• right-side
• Top
• Bottom.

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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.

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

• Is a form of perspective drawing in 3D.
• 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).

• No surface of the object is parallel to the
  paper, measurements parallel to isometric axes
  are to scale, angles are not.

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Isometric Drafting
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3.3 Oblique Projections

• Is a perspective drawing in 3D.
• An oblique projection is a perspective drawing in
  which one of the objects 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.

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Oblique Projections
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The Use of Projections in Engineering Drawings

• Multiple projections are combined in the
  engineering drawings for a project.
• Most commonly used are
• General drawings
• Axonometric Projections Exploded view drawings
• Detail drawings

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• 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.
• 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.

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General Drawing
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Exploded View
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Detail Drawing
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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 reduction reduce all measurements of an
  object by the same factor. 150 make measurements
  50 times smaller.
• Scale increase increase all measurements of an
  object by the same factor. 201 make measurements
  20 times bigger.
• Full-size object represented with its real
  measurements. 11 make the measurements exactly
  the same size.
• Drawings title block includes name of
  draftsperson, title of drawing, date when made,
  and scale that was used.

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Scale of 12
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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.
• A dimensional tolerance is an indicator of the
  maximum acceptable difference between a specified
  measurement and the actual measurement on the
  finished object.

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Tolerance

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

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Dimensioning

• 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 hole
• R radius of circle or curve
• - degrees of an angle

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Cross Sections and Sections

• Cross section reveals the interior of an object,
  exposing its hidden details to view.
• 1st step select dimension to imaginarily cut to
  produce cross-sectional view.
• For multiview projection use cutting plane line
• 2nd 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.

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• 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.

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Diagrams

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

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Symbols Used in Diagrams
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Common Types of Diagrams
Refer to diagrams of pliers
Using appropriate symbols
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Circuit Diagram