## 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

 5 A —

First angle projection

First angle projection

Third angle projection

Viewing direction

Viewing direction

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

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?
2 years ago
• may
How to construction angle projection?
2 years 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?
1 year ago
• Briffo
How could first angle projection is constructed?
1 year ago
• silvana
What is 1st angle and 3rd angke projection?
1 year ago
• Leonide
How to draw a first angle projection of a figure?
1 year ago
• Kevin
What is the purpose of first or third angle projection?
1 year ago
• Aliisa
Do japan draw 1st or 3rd angle?
11 months ago
• patrick
Who invented first angle projection?
10 months ago
• peter
Who invented the engineering drawing?
9 months ago
• danait mustafa
Why do you call it first and third angle projection?
4 months ago
• Fethawit
Why is it called first angle orthographic projection?
2 months ago
• kacper
Why do peoepl sue 1st and 3rd angle drawings?
2 months ago
• D
Why is it important first and third angle drawings?
2 months ago
• tuomas
What is the importance of first angle and third angle projections?
27 days ago