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Technical Drawing


Technical Drawing Designing things on paper Chapter 11 Questions 1. Two common drawings used in technology are: Engineering (or technical) Drawings and Diagrams. – PowerPoint PPT presentation

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Title: Technical Drawing

Technical Drawing
  • Designing things on paper

(No Transcript)
Conceptual Sketches
  • When you first get an idea for something you want
    to build you may draw it roughly, without using
    instruments or accurate scales. This is called a
    conceptual sketch.

Types of Drawings
All Drawings
Drawings (technical/engineering)
Diagrams (design technical)
Sketches (conceptual)
simulated perspective
Diagram (design plan)
Diagram (technical)
Oblique projection
Isometric projection
Multi view orthographic
Less technical
More technical
  • A conceptual sketch
  • Allows an idea to be expressed quickly in graphic
  • Is prepared free-hand (without drawing
  • Is not done to scale, but it respects the rules
    of technical drawing as much as possible, and is
    made roughly proportional to the object

Technical Drawings
  • Serve as a reference to workers, architects or
  • When you are ready to design the details, you
    make a technical drawing, done with more detail
    and more accuracy.

  • Sketch made without drafting tools... Just
    pencil and paper. Scale is approximate, not
    accurate, but the sketch should still look like
    the object.
  • Drawing made with drafting tools... Ruler, set
    squares, protractor and compass. Scale should be
    accurate and the drawing carefully made.

  • A technical drawing

Presents all the information necessary for the
objects construction. Is made with great
precision, Requires the use of rulers, compass
and protractor or drafting software. Is done to
scale, and respects the proportions of the object
represented. Respects conventions in the mode of
the representation.
Basic Lines (part 1)
Visible (Object) Line Represents the outline Thick Draw the visible object edges with these lines
Hidden Line Shows hidden details Medium dashed Draw hidden edges with these
Construction Line Used during drafting Fine Faint lines, sometimes coloured
Dimension Line Used to indicate a dimension Fine, with arrows 8cm Dimension extension lines go together!
Extension Line Used with a dimension line Fine Near arrows Dimension extension lines go together!
Center (Axial) Line Shows center or symmetry Fine With dash in middle
8 cm
Basic Lines (part 1)
Ghost Line Shows possible movement Fine dashed Sometimes in other color
Cutting plane line Position of a cross-section Thick With arrows Used only if you plan to draw a cross section
Hatched Lines Surface of a cross-section Fine Show where it is solid (section view only!!)
Long Break Shows that a line is shortened Fine With zig-zag Used only for large objects
Short break (cutaway) Object shortened or cut away Medium With curve
Leader Line Points to something Fine With bent arrow Attaches a comment or angle or dimension to an object.
Technical Drawing of Fighter Plane(Isometric
Projection, exploded view)
Technical drawings can represent things
  • as simple as a spoon,
  • or

Technical Drawing of a spoon Multi-view,
Orthographic projection
  • as complex as a space ship

Photograph of Mercury Spacecraft
Technical Drawing of Mercury Spacecraft, Top
View, Orthographic
? Technical Drawing of Mercury Spacecraft,
Isometric Projection
  • Perspective projections
  • Multi-view projections
  • Isometric projection
  • Oblique projection

True Perspective
Vanishing Point
  • Objects drawn in true perspective look realistic.
  • They have vanishing points where straight lines
    seem to converge
  • They can have one, two or three vanishing points,
    depending on how much the artist wants to work.
  • But in true perspective, objects far away will be
    drawn smaller than nearby objects not a good
    idea in technical drawing!

Vanishing Points
Vanishing Points
More True Perspective Drawings
  • Now that you have seen how nice perspective
    drawings can be...
  • We hardly ever use perspective projections when
    doing technical drawing.
  • They are too much work, and they dont show all
    the details we may need to show.
  • Also, they distort both angles and dimensions.
  • Leave them for ART class...

Isometric Projection(a simulated perspective
drawing style)
  • Isometric (or simulated perspective) drawings
    look at first like perspective drawings
  • But the lines dont converge. There are no
    vanishing points and distant objects are the same
    size as nearby ones.
  • Right angles in isometric projections are usually
    represented by 60 or 120 angles.

60 Represents 90
Represents 90
More isometric drawings
Warning Your workbook classifies isometric
drawings as perspective drawings, but they are
not true perspective. They resemble perspective
drawings but in a true perspective drawing,
distant objects are drawn smaller. In isometric
drawing, distant objects are not smaller..
Oblique Projectionanother simulated
This side is not!
  • Similar to isometric projection, it is also a
    simulated perspective
  • In oblique projections, the side of the object
    facing you is drawn square and accurate (that
    is with right angles at 90 and its measurements
  • The sides not facing you are distorted
  • Warning Your workbook calls this oblique
    perspective, but it is not a true perspective.

This side is accurate
90 60
Orthographic Projections
  • Orthographic projections flatten one view of
    the object onto a sheet of paper, while retaining
    the correct proportions (angles and dimensions)
  • Maps are an example of orthographic projection (a
    top view)
  • The trouble with orthographic projections is that
    one view usually isnt enough.
  • Maps and floor-plans are exceptions, where one
    top-view is often enough.

Orthographic Projection(Multi-view)
  • Draws an object as it would be seen from several
    different directions
  • The views are flat, with all angles shown
    correctly and all measurements to scale.

Comparing Projections
  • Perspective drawings look nicer when used by an
    artist, but
  • Isometric, oblique and multi-view drawings give
    more accurate information when used in technical
  • Isometric drawings show accurate dimensions, but
    distorted angles.
  • Oblique drawings give accurate dimensions for one
    side only.
  • Orthographic (multi-view) are the best choice for
    most technical drawing.

Orthographic (multi-view)
Comparison of Projections
Projection Used for Tested on
Orthographic (top view) Drafting, maps, floor plans Yes
Orthographic (multi-view) Technical drawings, drafting, conceptual sketches (sometimes) Yes
True Perspective (one, two or three point) Artistic drawing, conceptual sketches No
Isometric (simulated perspective) Conceptual sketches, technical drawings (sometimes) Yes
Oblique (simulated perspective) Conceptual sketches No
An Isometric Drawing
  • SCALE is the relationship between the measurement
    of an object drawn on a sheet of paper, and the
    measurements of the actual object.
  • Often technical drawings are made a different
    size from the objects they represent.
  • Scale-reduction is when the drawing is smaller
    than the actual object
  • Scale-increase is when the drawing is larger than
    the actual object.

  • When a drawing is done to scale, you should label
    it with its dimensions.
  • Use dimension lines to label each dimension, with
    extensions where necessary
  • You should label just enough edges to show all
    the dimensions, but you dont need to repeat.
  • In Canada (at least for science) dimensions are
    usually given in millimetres (mm). If you use
    different units (cm, in, feet etc.) you need to
    write the unit. You do not need to write mm if
    all of your dimensions are in millimetres.
  • Angles can be shown in degrees (), diameter by
    Ø, and radius by R

300 means 300mm unless another unit is specified
A Toy Truck
How to label an angle.
Ø means diameter (R would be radius)
How to label small dimensions.
Dimensions can also be shown on isometric
drawings, but you have to be a bit more careful.
Also, you should only show the most important
dimensions on an isometric drawing.
  • Diagrams are simplified versions of a drawing.
    Diagrams show how an object works, not
    necessarily how it looks.
  • Diagrams often use abstract symbols rather than
    actual pictures to represent things.

A Circuit Diagram
  • Doesnt show what the circuit looks like, but
    tells an electrician how its all connected.

Diagram of Energy Conversion Unit
  • It doesnt show what the unit looks like, but
    rather, what it does or how it works.

Exploded Views
  • A diagram that shows an object taken apart is
    sometimes called an exploded view.

Chapter 11 Questions
  • 1. Two common drawings used in technology are
    Engineering (or technical) Drawings and Diagrams.
  • 2. Technology is a set of techniques used by
    humans to design, build, and maintain objects and
    systems that we need or want.
  • 3.

(a) Basic Line (b) Function
1 Dimension Line Indicates the length of an object
2 Extension Line Shows boundaries of a measurement
3 Visible (or Object) Line Shows Visible outlines of an object
4 Hatching Indicates surface in a section view
5 Leader (or Reference) Line Ties a dimension (or a label) to a feature
6 Hidden Line Indicates hidden outlines
7 Centre (or symmetry) Line Indicates the center of a circle
(c) Cutting Plane lines and Construction Lines
are not shown.
  • 4. Geometric Lines
  • A) the main drafting instruments are T-square,
    set-squares, ruler, pencil and compass
  • B) The three types of straight line are
    horizontal, vertical, and oblique.
  • C) Two drafting instruments that can draw circles
    are the compass and the circle template.
  • 5. The Stop Signs The stop sign on the left is a
    sketch, since it appears to be drawn freehand.
    The one on the right was drawn using tools.
  • 6. Projections
  • A) The rays are perpendicular in multi-view and
    isometric projections
  • B) these are called orthogonal projections

  • 7. The six views are
  • Top view, Front view, Right Side view
  • Bottom view, Back (or Rear) view, Left Side view
  • 8. The three drawings
  • 1 oblique projection, 2 isometric, 3
    multi-view (or orthographic view)
  • 1 and 2 are the perspective drawings.
    (actually they are simulated perspective
    drawings rather than true artistic perspective)
  • A matches 3, B matches 1
  • C matches 4, D matches 2

  • 10. Jonathan is building a model car. He is
    reducing the measurements 40 times.
  • The scale he is using is a scale reduction.
  • It is indicated by 140
  • The finished model will be 100 mm long (or 10 cm)
  • 11. The diagram of the soccer field has a scale
    of 12000, so... (hint use your ruler)
  • The width of the actual field is 68000 mm (or
  • The length of the actual field is 104000 mm
  • 12. The dimensions of the skateboard are
  • Length 790 mm (or 79 cm)
  • Width 210 mm (or 21 cm)
  • Diameter of wheels 60 mm

  • 13. The maximum difference between the
    measurement on the diagram, and the real-life
    measurement is called the tolerance.
  • 14. Match the objects to their cross sections
  • A matches 1
  • B probably matches 3, (but could match 2)
  • C probably matches 2, (but could match 3)
  • 15. Look at the diagram of the wrench.
  • Section B is octagonal
  • Section C is circular (or round)
  • The sections are aligned, they are shown inside
    the drawing of the wrench instead of outside of

  • 16. Diagram of kitchen scale
  • A) The force is exerted on the tray
  • B) 7 regular screws were used, plus one bolt
    (which is a type of screw) so I would also accept
    an answer of 8.
  • C) The rod can move up and down ( or, more
    accurately, has bidirectional translation)
  • D) The coil spring allows the rod to return to
    its initial position.

  • Technology Technical Drawing
  • Basic Lines Geometric Lines
  • Sketch Projection
  • Isometric (projection) Oblique (projection)
  • Orthagonal (proj.) Multiview (projection)
  • General drawing Exploded drawing
  • Detail drawing Scale
  • Dimensioning Tolerance
  • Section Cross section
  • Diagrams design, technical, and circuit

Basic Lines to Know
  • Visible(or object)
  • Hidden
  • Construction
  • Centre
  • Dimension and extension
  • Cutting Plane
  • Hatching
  • Leader (or reference)

Geometric Lines to know
  • Horizontal (straight)
  • Vertical (straight)
  • Oblique
  • Ellipse (and circle)
  • Curve

Methods of Drawing
  • Sketching
  • Drafting
  • Computer Assisted Design (C.A.D.)

  • Multiview (orthagonal)
  • Isometric
  • Oblique

  • Dimensioning
  • Calculating Scale

  • Design plan diagrams
  • Technical diagrams
  • Circuit diagrams
  • Symbols for
  • Forces or constraints
  • Movement
  • Parts (screw or bolt, nut, guides)
  • Electrical circuits