RECTANGULAR DIMETRY PROJECTION

Dimetryis an axonometric projection with the identical indexes of the distortion on two axes. Figure 3.4,а shows a sphere in a rectangular dimetric projection the diameter of which equals a metage. A corner between a horizontal line and the axis X equals 7°10’, and the axis of Y - 41°25’. Place this sphere into a cube ribs of which, are equal the direction of axonometric axes X and Z, and to the direction to axes Y a rib in rectangular dimetry will look half less (figure 3.3,b). Project a sphere on the verge of a cube. The projections of a sphere on the verge of a cube are smaller in sizes (disfigured). That segment of coordinate ax of 1 mm long in rectangular dimetry will be represented in a segment of 0,94 mm long to direction of axes X and Z, and by a segment of 0,47 mm long to direction of axes Y. Correlation 1 / 0,94=1,06 times determines a coefficient down-scaling on which we increase a sphere (figure 3.3,c). Now the projections of a sphere as ellipses are inscribed in the verge of a cube (see figure 3.3,d). The major axis of ellipses is 1,06 diameter – D of projection circle of a sphere (equator, frontal meridian, type meridian), and minor axis is a 0,95 diameter on the frontal plane of projections and 0,35 diameter on horizontal and profile planes. Place a sphere in the usual (europian) first angle projection method. Figure 3.3,e shows the correlation for determination of the length of cuttings-off of major axis [AB] and minor axis [CD] of an ellipse on the frontal plane of projections and minor axis- [EF ] ellipses on horizontal and profile planes. The size of the sections [1, 2] and [3, 4] is equal to the diameter of the projection circle of a sphere (in general case to diameter of a cylinder or a hole on a figure), and the section [5, 6] to the half of diameter of the projection circle of a sphere. While making sectional drawings in rectangular іzometry follow the rules of hatching as shown in figure 3.3,f.

а) b)

c) d)

e) f)

Figure 3.4 – Dimetry