Manual of Purpose-Made Woodworking Joinery

Orthographic projection 11

DIMENSION LINES AND

FIGURES

Figures 2.3(a)(b)(c): Dimension lines with open
arrowheads, illustrated below at (a), are meant to be
used for basic/modular (unfinished) distances, spaces
or components. The more commonly used dimension
lines, illustrated at (b), with solid arrow heads, are used
for finished work sizes. All dimension figures should
be written above and along the line; figures on vertical
lines should be written, as shown at (c), to be read
from the right- hand side.

SPECIAL- PURPOSE LINES

Figures 2.4(a)(b)(c)(d)(e): So- called section lines seen
on drawings indicate imaginary cutting planes drawn
at a particular point through the plan- or elevational-
views, to indicate that a detailed, exposed view at this
point is shown separately. The views of such exposures
are called sectional views and are lettered A- A, B- B
and so on, according to the number of sections to be
shown. It is important to remember that the arrows
indicate the direction of view to be shown on a sepa-
rate section drawing.

HIDDEN DETAIL

Figure 2.5: Hidden detail, or work to be removed, is

sometimes indicated by a broken line. This is usually

done on graphical drawings, especially in textbooks.

BREAK LINES

Figures 2.6(a)(b): End break- lines at (a), symbolized

by a zigzag pattern, indicate that an object is not fully

drawn. Central break- lines, as shown at (b), indicate

that the object is not drawn to scale in length, even

though the true measurement is given.

CENTRE LINES

Figure 2.7: Centre- or axial- lines on drawings are

indicated by a thin dot- dash chain.

ORTHOGRAPHIC PROJECTION

Orthography is a Latin/Greek- derived word meaning

correct spelling or writing. In technical drawing the

word is used to mean correct drawing. Orthographic

projection, therefore, refers to a conventional drawing

method used to display the correct layout of the

Figure 2.3 (a) Open arrow- heads for unfinished work (b)
Solid arrow- heads for finished work and (c) Measurement
read from the right- hand side.

2.500 m 0.600 m

0.200 m
(a) (b) (c)

Figures 2.4 (a)(b)(c)(d)(e) Section

lines A- A, B- B, C- C, D- D and E- E.

AA

BB

C

C

D

D

E

E

Horizontal sections

Vertical sections

Staggered section

(a)

(b) (c) (d) (e)

Figure 2.5 A broken line indicates hidden detail – or

work to be removed.

Figure 2.6 (a) End break- lines (b) Central break- lines.

1.

(a) (b)

Figure 2.7 Centre- or axial- line.