Transcript Technical Drawing Theory

3rd Angle Symbol
3rd Angle Orthographic Projection
3rd Angle projection
In 3rd Angle the SIDE and the END views are
always viewed from ground level and they are
positioned next to each other. The END view is
positioned to the right of the SIDE view. The
PLAN view is always a view of the object as seen
from above and is always positioned above the
SIDE view.
What is seen on the right is drawn on the right.
1st Angle Orthographic Projection
In 1st Angle the SIDE view and END view are still
positioned next to each other. The END view is
still positioned to the right of to the right of the
SIDE view. The PLAN view, however, is positioned
below the SIDE view.
1st Angle projection
1st Angle Symbol
What is seen on the left is drawn on the right.
1)
Hidden Detail lines
ROD
SIDE VIEW
Hidden Detail and Sectional Views
END VIEW
The technique of showing hidden detail and sectional
views of objects are useful when information needs to
be displayed which cannot normally be seen because it
is either behind, inside or below the surface.
Hidden detail is shown as dotted lines.
PLAN VIEW
1)
In picture one a rod is shown with a hole in one
end. By using the two orthographic views and the
HIDDEN DETAIL lines it can be seen that the rod is
hollow.
2)
In picture two the cube appears hollow through
its length. By using the two orthographic views
and HIDDEN DETAIL lines it can be seen that the
cube has a solid base.
2)
Hidden Detail lines
Sectional Views
CUBE
SIDE VIEW
Cut through a chocolate bar with a knife. The
inside will be visible along with the thickness of
the chocolate coating. When producing a
sectional view solid material which has been
sliced through is detailed with 45° hatched lines.
45° hatched lines
3)
3)
CUP
SECTIONAL VIEW
In this picture the sectional view of a cup has
been shown to illustrate the hatched lines to
shown a solid area sliced through. These lines
should be equally spaced.
Oblique Projection
3rd Angle projection
This is the simplest form of drawing in
3D, but it is also the least realistic.
- Start by drawing a true side view of
the object on a horizontal base.
Cavalier oblique
All lines true length
unrealistic.
45°
Cabinet oblique
45° lines half true length
more realistic.
45°
- All other horizontal lines are then
drawn at 45°.
If the 45° lines are drawn their true
length it gives an unrealistic
appearance called CAVALIER
OBLIQUE. To create a more realistic
appearance the 45° lines are drawn
half their true length this is called
CABINET OBLIQUE.
Isometric Projection
3rd Angle projection
A more complicated view which does not
include a true face, this method produces
a more realistic effect than the oblique
projection.
- Start by drawing the leading vertical edge
(the edge closest to the viewer).
Isometric projection
All lines are true length.
- All other horizontal lines are then drawn
at 30°.
- All lines are drawn their true length.
30°
30°
Freehand Isometric crate, used to
produce more complex shapes.
Isometric is also a useful technique for
freehand sketching. An isometric crate is
drawn freehand over which the object is
drawn.
This crating technique is used by designers
from all fields, architecture to jewellery
design.
Compass Construction – Bisection and Division of lines
Bisection of a line – A line can be divided in half by using a pair of
compasses. With the compass opened by a distance greater than
half of AB, strike arcs from A and B. A line joining the points of
intersection of the arcs will bisect the line at 90°.
B
A
B
A
Division of a line into equal parts – A line of unknown length can
be divided into any number of equal parts. Draw a line AB of
unknown length. From A draw a line AC at any angle, make three
convenient equal divisions. Join the last division with B. Place a set
square on that line and a ruler underneath the set square, then
draw parallel lines at your 2 other marks. Line AB is now equally
divided into three parts.
C
B
A
C
Division of a line into a ratio of parts – A line of unknown length
can be divided into a ratio of parts using the same technique for
division into equal parts. Draw a line AB of unknown length to be
divided into the ratio of 3:4. From A draw a line AC at any angle.
Make 7 (3+4) equal divisions. Join division 7 with B and from
division 3 draw a line parallel to 7B.
Compass Construction – Bisection and Division of Angles
Bisection of a right angle – A 90° angle can be bisected to produce
two 45° angles with a pair of compasses. With centre O, draw any
convenient arc cutting the angle at A and C. Place the compass
point at A and open to see and strike an arc. Move the compass
point to C and open to A striking an arc to intersect the previous.
Draw a line from O through the intersecting arcs. Each angle will
now be 45°.
A
C
O
A
O
A
Bisection of an angel of 45° – Proceed as for a right angle. An angle
of 45° will be divided into two angles of 22.5°. This method can be
used to bisect any angle.
C
X
Y
O
C
Division of an angle into equal parts – To divide a right angle into
three equal parts, draw a convenient arc with centre at O touching
the two sides of the right angle. Label these points A and C. With
the same radius, draw arcs from C and A to cut at X and Y. Each
angle will be 30°.
Compass Construction – Construction of Angles
A
B
O
B
A
P
Perpendicular at a point on a line – At point O, draw a
semicircle of any radius to touch the line at A and B. With the
compasses opened to a greater radius, strike arcs from A and B.
The line drawn from point O through the intersection of the
two greater arcs will be perpendicular to the base line.
Perpendicular at the end of a line – Point O is at the end of a
line. From this point draw a convenient arc to touch the line at
P. With the same radius step of points A and B. From A and B
strike arcs of the same radius. The line draw from point O
through the intersection of these two Arcs will be perpendicular
to the base line.
O
Using this technique it is possible to draw a square if the length
of the initial line is know.
Compass Construction – Construction of Angles
A
Angle of 60° – At point O, draw a convenient arc to
touch the line at point P. With the same radius, step of
point A from point P. The angle produced will be 60°.
P
O
Angle of 120° - At point O, draw a convenient arc to
touch the line at P. With the same radius, step off points
A and B. The angle produced will be 120°.
A
B
O
P
A
E
E
B
Transference of Angles – Draw any angle ABC and from
B draw a convenient radius to touch points E and D. To
transfer the angle, draw line BC and the arc of radius BD.
Strike of distance DE on the arc.
D
C
B
D
C
Compass Construction – Regular Hexagons
A/C
Compass Method – Draw a circle of a given radius. With the
same radius, step of points around the circumference of the
circle. Six equal divisions will give a regular hexagon inside
the circle. The radius is equal to the length of one side of the
hexagon.
Set Square Method Given Distance A/C – This method draws
the hexagon inside the circle. Draw a circle of diameter A/C
(distance across the corners). Draw centre lines and
diagonals as shown using a 30° 60° set square. Complete the
hexagon by joining the diagonals.
A/F
Compass Construction – Regular Hexagons
Set Square Method Given the Distance A/F – This
method draws the hexagon outside the circle. Draw a
circle of diameter A/F (distance across the flats). Draw
centre lines and diagonals as shown using a 30° 60°
set square. Complete the hexagon using the same set
square drawing tangents at right angles to the
diagonals.
8
6
7
5
4
3
1
2
A
B
Set Square Method Given Base – This method uses a
30° 60° set square. Given the base line A/B the
hexagon can be draw by projecting the lines in
numbered order.
1
3
2
4
Compass Construction – Regular Pentagons
This technique can be used for any regular sided shape inside a circle. Evenly divide
the angled line for the amount of sides on the shape. Use division of a line to ratio the
diameter line with the last and second mark.
5
6
7
8