3rd Angle Orthographic 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.

What is seen on the left is drawn on the right.1st Angle projection

3rd Angle projection

3rd Angle Symbol

1st Angle Symbol

Hidden Detail and Sectional Views

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.

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.

Sectional Views

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.

3) 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.

Hidden Detail lines

SIDE VIEW END VIEWROD

1)

2)

PLAN VIEW

SIDE VIEW

Hidden Detail lines

CUBE

3)

CUP SECTIONAL VIEW

45° hatched lines

Oblique 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.

- 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.

3rd Angle projection

Cavalier obliqueAll lines true length unrealistic.

45°

45°

Cabinet oblique45° lines half true length more realistic.

3rd Angle projection

Isometric 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).

- All other horizontal lines are then drawn at 30°.

- All lines are drawn their true length.

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.

Isometric projectionAll lines are true length.

30°30° Freehand Isometric crate, used to produce more complex shapes.

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°.

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.

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.

A B

A B

C

A

C

B

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°.

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.

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°.

O C

A

O C

A

O C

A X

Y

Compass Construction – Construction of Angles

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.

Using this technique it is possible to draw a square if the length of the initial line is know.

OA B

P O

BA

Compass Construction – Construction of Angles

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°.

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°.

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.

PO

A

PO

BA

C

A

B

E

DCB

E

D

Compass Construction – Regular Hexagons

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/C

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.

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.

A/F

A B

12 3

456 7

8

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.

3 4

5

1

6 7 8

2