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UNIT 7 �GRAPHICAL DETAILING �IN CONSTRUCTION

Dr Adewale Abimbola, FHEA, GMICE.

www.edulibrary.co.uk

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Aim & Objectives

Aim: Orthographic Projections

Objectives: At the end of the lesson, the students should be able to:

  • Define orthographic projection.
  • Discuss the purpose of orthographic projection.
  • Produce first and third orthographic projections of various objects.

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Elevations

  • Elevations are the sides of an item/object.
  • The top is referred to as the ‘plan’.
  • These drawings enable detailed measurements to be added for every section of the product.

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Orthographic Projections

  • Orthographic projections are working drawings in either a first or third angle projection.
  • They show each side of a design without perspective, i.e., a 2D drawing of a 3D object.
  • They are used to show an object from every angle to help manufacturers plan production.
  • Starting with a front view of a product, construction lines show where areas join and are used to draw a side and plan (top) view, ensuring that the drawing is accurate from all angles. These drawings are to scale and must show dimensions.

Third angle orthographic projection.

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Orthographic Projections

First and third-angle projections

  • First angle projections and third angle projections are the two main types of orthographic drawing, also referred to as ‘working drawings’.
  • The difference between first and third angle projection is in the position of the plan, front, and side views.
  • In the third angle, what you see from the right would be drawn on the right.
  • In the first angle, the view from the right would be projected through and drawn on the left.
  • In a first-angle projection, the plan view is below the side view, whereas in a third-angle projection the plan view is above the side view

First angle projection (Indovance, 2022)

Third angle projection (Indovance, 2022)

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Orthographic Projections

  • First and third angle projections use these symbols on a diagram to indicate which projection they are.
  • Orthographic projections have a set of standard lines to show different aspects of the diagram.
  • These lines allow complex shapes to be drawn simply in 2D.

Third angle projection

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Orthographic Projections

Third angle projection

  • In the third angle, what you see from the right would be drawn on the right.

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Orthographic Projections

First angle projection

  • In the first angle, the view from the right would be projected through and drawn on the left.

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Self-assessment Task

Using the manual drafting technique, produce the first and third orthographic projections of the following objects.

All dimensions in cm

All dimensions in mm

Front view

Side view

Plan

Front view

Side view

Plan

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References/Bibliography

  • Indovance (2022) Understanding first angle projection vs. third angle projection in engineering drawings. Available at: https://www.indovance.com/knowledge-center/understanding-first-angle-projection-and-third-angle-projection/ (Accessed: 20 October 2023).
  • Pearson (2017) BTEC national construction student book. London: Pearson.
  • Topliss, S., Mohyuddin, S. A., Murray-Smith, J. and Stokes, A. (2013) BTEC first: construction and the built environment. Essex: Pearson Education Limited.

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