Why are first and third angle projections so named

The terms first angle projection and third angle projection may seem like complicated terms but the reason for their naming is connected with geometry. Figure 2.15 shows four angles given by the planes OA, OB, OC and OD. When a part is placed in any of the four quadrants, its outline can be projected onto any of the vertical or horizontal planes. These projections are produced by viewing the parts either from the right-hand side or from above as shown by the arrows in the diagram.

In first angle projection the arrows project the shape of the parts onto the planes OA and OB. When the two planes are opened up to

Viewing direction

5

A —

First angle projection

First angle projection

Third angle projection

Viewing direction

Viewing direction

First Angle And Third Angle
Figure 2.15 Geometric construction showing the meaning of first and third angle projection

180°, as shown in the small diagrams in Figure 2.15, the two views will be in first angle projection arrangement.

When the part in the third quadrant is viewed from the right-hand side and from above, the view will be projected forwards onto the faces OC and OD. When the planes are opened up to 180°, the views will be in third angle projection arrangement, as shown in the small diagrams in Figure 2.15.

If parts were to be placed in the second and fourth quadrant, the views projected onto the faces when opened out would be incoherent and invalid because they cannot be projected from one another. It is for this reason that there is no such thing as second angle projection or fourth angle projection.

There are several ISO standards dealing with views in first and third angle projection. These standards are: ISO 128:1982, ISO 128-30:2001 and ISO 128-34:2001.

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Responses

  • adonay
    What is the definition of the third angle angle projection?
    8 years ago
  • pansy
    What is first and third angle projections?
    8 years ago
  • azzeza
    What is meant by first angle projection?
    8 years ago
  • kristiina
    Why are first and third angle projections so named?
    8 years ago
  • Amedeo
    How to interpret first and third angle drawings?
    8 years ago
  • Lobelia
    Why is first angle projections called that?
    7 years ago
  • ulla-maj
    How to draw a first angle projection in workshop techniques?
    3 years ago
  • David
    Why is 3rd angle projection so called?
    3 years ago
  • Amanda
    Why is first angle projection popularly named?
    2 years ago
  • petra walter
    What is the meaning of first angle projection and third angle projection. com?
    2 years ago
  • remigio
    What informed the naming: 1st angle projection?
    2 years ago
  • Jean
    What is the difference between the 3rd angel and 1st angel projections?
    2 years ago
  • marigold
    What is d/f from first and therd angel projection?
    1 year ago
  • may
    How to construction angle projection?
    1 year ago
  • Kenzie
    Why is the projection shown on an engineering drawing?
    1 year ago
  • manuela
    Why is first angle projection termed?
    1 year ago
  • asmara
    Why use first and thord angle drawings?
    10 months ago
  • Briffo
    How could first angle projection is constructed?
    10 months ago
  • silvana
    What is 1st angle and 3rd angke projection?
    9 months ago
  • Leonide
    How to draw a first angle projection of a figure?
    9 months ago
  • Kevin
    What is the purpose of first or third angle projection?
    8 months ago
  • Aliisa
    Do japan draw 1st or 3rd angle?
    7 months ago
  • patrick
    Who invented first angle projection?
    5 months ago
  • peter
    Who invented the engineering drawing?
    4 months ago

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