What Is Isometric Projection | Principle of Isometric Projections | Isometric Scale

What Is Isometric Projection?

Isometric projection is a method for visually representing three-dimensional objects in two dimensions in technical and engineering drawings.

It is an axonometric projection in which the three coordinate axes appear equally foreshortened and the angle between any two of them is 120 degrees.

Pictorial projections are utilized for presenting ideas that might be easily understood by persons, even without technical knowledge and training of multi-view drawing.

The Pictorial drawing shows several faces of an object in one view, approximately as it appears on the eye.

Principle of Isometric Projections

It’s a pictorial orthographic projection of an object where a transparent cube containing the object is tilted before one of those solid diagonals of the cube becomes perpendicular to the vertical plane along with the three axes are equally inclined to this vertical plane.

The isometric projection of a cube in steps is shown in the below figure-1. Here ABCDEFGH is the isometric projection of the cube.

1- Principle of Isometric Projections

The front view of this cube, resting on one of its corners (G), is the isometric projection of the cube. The isometric projection of the cube is reproduced shown in the below figure-2.

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Isometric Scale

In the isometric projection of a cube shown in the show above figure-2, the top face ABCD is sloping away from the observer, and hence the edges of the top face will appear fore-shortened.

The true shape of the triangle DAB is represented by the triangle DPB. The extent of reduction of an isometric line is easily found by the construction of a diagram known as isometric scale.

For this, reproduce the triangle DPA as shown in the show below figure-3. Mark the divisions of true length on DP. Through these divisions, draw vertical lines to get the corresponding points on DA.

The divisions of the line DA give dimensions to isometric scale. In the triangle ADO and PDO at the show above figure-2 ( An Isometric Cub), the ratio of the isometric length to the true length,

i.e., DA/DP = cos 45° /cos30° = 0.816

The isometric axes are reduced in the ratio 1:0.816, i.e., 82% approximately.

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Lines in Isometric Projection

The following are the relations between the lines in isometric projection which are evident from the show above figure-2 ( An Isometric Cub)

1. The lines which are parallel to the object are parallel at the isometric projection.
2. Vertical lines on the object appear vertical at the isometric projection.
3. Horizontal lines on the item are drawn at an angle of 3 0° with the horizontal at the isometric projection.
4. A line parallel to an isometric axis is called an isometric line, and it’s fore-shortened to 82 percent.
5. A line that’s not parallel to any isometric axis is known as the non-isometric line, and the extent of the fore-shortening of non-isometric lines is different if their inclinations with the vertical planes are different.

Isometric Projection Views

Shows in below Figure (a) rectangular block in pictorial form and Shows in below Figure (b), the steps for drawing an isometric projection using the isometric scale.

a – Isometric Projection

b – Isometric Projection

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Isometric Drawing

Drawing of objects are seldom drawn in true isometric projections, since using an isometric scale is inconvenient.

Instead, a convenient way in which the foreshorten-ing of lengths is ignored and actual or true lengths are utilized to obtain the projections, known as isometric drawing, or isometric perspective is normally utilized.

This is advantageous because the measurement could be made directly from a drawing. The isometric drawing of the figure is slightly larger (approximately 22%) than the isometric projection.

Since the proportions are the same, the increased size doesn’t affect the pictorial value of this representation, and at the same time, it might be done quickly.

Shows in below a figure the difference between isometric drawing and isometric projection.

Isometric Drawing

• Steps to be followed to make an Isometric drawing from orthographic views are given below
• Study the given views and note the principal dimensions and other features of this object.
• Draw the isometric axes (a).

a- Otrhographic View

• Mark the principal dimensions to-their true values along the isometric axes (b).

b- Isometric View

• Complete the housing block by drawing lines parallel to the isometric axes and passing Through the above markings (c).

c- Isometric View

• Locate the principal corners of all the features of the object on the three faces of the Housing block (d).

d- Isometric View

• Draw lines parallel to the axes and passing through the above points and obtain the isometric Drawing of this object by darkening the visible edges (e).

e- Isometric View

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