It is aometimes necessary to draw circles or curves on faces which are not parallel to any of the three isometric axes Fig. 3/7 shows a cylinder cut at 45*. Two views of the cylinder have to be drawn: a plan view and an elevation. The plan view is divided into stripe and the positions of theee stripe are projected onto the elevation.
The base of the cylinder is drawn in isometric in the usual way. Points 1 to 20. where the strips cross the cncI* ere projected vertically upwards and the height of the cylinder, measured from the base with dividers, is transferred for eech point in turn from the elevetion to the isometric view. These points are then carefully joined together with a neet freehand curve.
True isometric projection
Isometric projection is a method of drawing with instruments which gives a pictorial view of an object. It is not often used in industry and. when it is used, the vast majonty of drawings would be made using conventional isometric projection. Conventional isometric is a distorted and simplified form of true isometric. True isometric is found by taking a particular view from an orthographic
Fig 3/8 True isometric projection
projection of an object. Fig. 3/8 shows a cube, about 26 mm side, drawn in orthographic projection with the cube so positioned that the front elevation is a true isometric projection of the cube. The three Isometric axes are still at 120" to each other. In conventional isometric, distances measured parallel to these axes are true lengths. In true isometric projection they are no longer true lengths although they are proportional to their true lengths. How-
m TRUE. LENGTH
Fig 3/8 True isometric projection ever, the horizontal distances on a true isometric projection are true lengths. The reduction of lengths measured parallel to the isometric axes makes the overall size of the true isometric drawing appear to look more natural, particularly when directly compared with an orthographic or plane view of the same object (compare the relative sizes of the prism in Fig. 3/2).
If the horizontal length and the length parallel to the isometric axes were both to be true lengths, the Isometric axes would have to be at 49» (Fig. 3/9). Since the isometric axes are at 30®. the 45° lengths must be reduced.
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