1.
LESSON 6: PREPARE AND INTERPRET TECHNICAL
DRAWING
ILLUSTRATION 7

2.
LO 1. ANALYZE SIGNS, SYMBOLS, AND DATA

3.
BASIC TECHNIQUE – LINES AND LETTERS
ALPHABET OF LINES (FOR TECHNICAL DRAWING)
The use of line types on a drawing are used to describe the various
features of an object to the person reading the print. A line is the most
fundamental and perhaps the most important, single entity on a technical
drawing. Lines help to illustrate and describe the shape of objects that will later
become real parts.

4.
BASIC TECHNIQUE – LINES AND LETTERS
ALPHABET OF LINES (FOR TECHNICAL DRAWING)

5.
It is important to distinguish between line patterns to make your
drawing legible.
The line patterns in Figure A are examples of good freehand
quality. Figure B shows examples of good and poor technique.
Figure A
Figure B
BASIC TECHNIQUE – LINES AND LETTERS

6.
BASIC TECHNIQUE – LINES AND LETTERS
1. OBJECT OR VISIBLE LINES – Thick dark line use to show outline of object, visible edges and surfaces.
2. CONSTRUCTION LINE – Very light and thin line use to construct layout work.
3. DIMENSION LINE – Thin and dark lines use to show the size (span) of an object with a numeric value.
Usually terminates with arrowheads or tick markings.
4. HIDDEN LINE – Short dash lines use to show non visible surfaces. Usually shows as medium thickness.
5. CENTRE LINE – Long and short dash lines. Usually indicates center of holes, circles and arcs. Line is thin
and dark.
6. EXTENSION LINE – Thin and dark line use to show the starting and ending of dimension.
7. CUTTING PLANE LINE – Extra thick line use to show cutaway views or plane of projection where a
section view is taken. Arrow indicates direction of view.
8. SHORT AND LONG BREAK LINES –Short and long medium line use to show cutaway view of a long
section.
9. LEADER LINE – Medium line with arrowhead to show notes or label for size or special information about
a feature.
10. PHANTOM LINE – Long line followed by two short dashes use to show alternate position of a moving
part.
11. SECTION LINE – Medium lines drawn at 45 degrees use to show interior view of solid areas of cutting
plane line.

7.
Lineweights
• 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 thick and light.
BASIC TECHNIQUE – LINES AND LETTERS

8.
BASIC TECHNIQUE – LINES AND LETTERS

9.
BASIC TECHNIQUE – LINES AND LETTERS
line quality
• Use a soft pencil (e.g. 0.5mm HB) to achieve a range of tone from light
guidelines that will not show on a photocopy to very dark grey lines that
will photocopy black. Provided that you are not too heavy handed, even the
darkest lines can be erased without leaving a grey smudge on the paper.
• Lines drawn quickly and confidently look better. A slow, shaky line looks as
though it does not know where it is going.
• Sharp lines tend to magnify errors. Fuzzy edged shapes usually ‘appear’
more as they should.

10.
BASIC TECHNIQUE – LINES AND LETTERS
straights
• Lightly mark points at each end of the
intended line. Move your pencil between the
points a couple of times, with the pencil point
just clear of the paper, to ‘teach it the route’.
• Draw several guidelines between the points
and then go over the ‘best line’ more firmly.

11.
BASIC TECHNIQUE – LINES AND LETTERS
curves
• Use parts of complete ellipses or circles as guidelines for the curve.
• For complex curves, use a join the dots technique.
lettering
• Rule horizontal guidelines to define character height (i.e. top and
bottom) and line spacing.
• Judge character length and spacing of characters and words by eye
unless the lettering needs to be very large.

12.
BASIC TECHNIQUE – SHAPES
SHAPES
• Construct shapes using lines. Most of your lines will be guidelines so draw
them to be either nearly invisible or easily removable.
• Use diagonals to find the center of a square or rectangle, either for sub-
division into smaller squares or rectangles or for the construction of circles
or ellipses.
• The distance from the center of a circle to its perimeter is constant (!). A
circle will touch an enclosing square at the center of each of its edges.
• As a square squashes to a rectangle, so a circle squashes to an ellipse. The
ellipse is symmetrical about two axes and it still touches the squashed
square at the center of its edges.
• A very close approximation of an ellipse can be constructed with circular
curves of two different radii.

13.
BASIC TECHNIQUE – SHAPES

14.
BASIC TECHNIQUE – SOLIDS
SOLIDS
• Construct solids from lines and complete shapes, using light guidelines for both
seen and unseen edges of the object.
• Go over or erase your light guidelines only when completely satisfied.
• A square approximates to a diamond when viewed at an angle. Draw a circular
bar by constructing ellipses on the ends of an enclosing square prism.
• Apply line shading parallel or perpendicular to the slope of a plane to indicate
form.
• A variety of techniques may be used to suggest a curved surface.
• Subtlety is lost in the photocopier or fax. so bear in mind how your sketch is to
be reproduced.

15.
BASIC TECHNIQUE – SOLIDS

16.
ORTHOGRAPHIC
Orthographic projection is a means of representing three-dimensional objects in two dimensions.
The 3 main views are (top, front, and right view).

17.
ISOMETRIC
Isometric drawing is way of
presenting designs/drawings in three
dimensions. Designs are always drawn
at 30 degrees in isometric projection.

18.
PERSPECTIVE
A form of pictorial drawing
in which vanishing points
are used to provide the
depth and distortion that is
seen with the human eye.
Perspective drawings can
be drawn using one, two,
and three vanishing points.

19.
PERSPECTIVE
Basic principles
• What the eye sees without distortion is within a 60˚ cone of vision. Bear this in mind when
deciding on the position of your viewpoint relative to what is to appear as the foreground of
your sketch.
• In front view perspective, there is one vanishing point. In angular perspective, there may be
two or more vanishing points.
• A vanishing point often needs to be beyond the border of the sketch for a view that does not
appear distorted. Sketch in ‘by eye’ guidelines that converge to a common vanishing point
outside the drawing area - the exact location of remote vanishing points is not necessary.
• A perspective grid can be used as an aid to drawing objects at the correct relative distance
size to one another.
• Simple line shading can be used to indicate shape and form, with the amount of detail shown
reducing with distance.

20.
OBLIQUE
Oblique projection is a method of
drawing objects in 3 dimensions. It is a
type of drawing involving a combination
of a flat, orthographic front with depth
lines receding at a selected angle,
usually at 45 degrees.

21.
Sources:
https://www.art-is-fun.com/grid-method
https://www2.psych.ubc.ca/~rensink/courses/psyc579/07.2-notes.pdf
https://www.peachpit.com/articles/article.aspx?p=2873372&seqNum=3
http://project-handbook.pbworks.com/w/file/fetch/52453142/SWAILES_CC1016_sketching.pdf
https://civilseek.com/free-hand-sketching/
https://schoolworkhelper.net/technical-drawing-alphabet-of-line/