Axonometric projections in technical drawing

When carrying out technical drawings, along with tracing objects and details in orthogonal projections, you need to have more visual images. For this, a method of axonometric construction is used.

It consists in the following: the object, together with the coordinate system (mutually perpendicular to the X, Y, Z axis) with which it is connected in space, is projected parallel to the plane of axonometric projections (or the picture plane). The projection of an object on this plane is called axonometry. It also displays axes of coordinates, called axonometric axes. It should be borne in mind that the direction of projection should be chosen in such a way that there is no coincidence with any of the coordinate axes.

Axonometric projections with perpendicular projection are called rectangular or orthogonal, and with non-perpendicular projection are oblique.

Usually the object is placed so that on the picture surface you can see the three sides of the object: bottom, top, front, left or right. Axonometric drawing should give the most complete idea about this subject, its magnitude and constructive form. Its main advantage is its clarity.

All axonometric projections can be classified as follows:

1. Isometric. In this case, all three axes of coordinates have the same slope, and all dimensions along the direction of the three axes have the same decrease.

2. Dimensional. Two coordinate axes in these projections have the same slope, and the third axis is different. Accordingly, in the two first axes, the reduction in size will be the same, and the third will be different.

3. Trimetric. All three axes in this case have a different slope and a decrease in dimensions is different for all three axes.

By placing the object shown differently on the surface and choosing a different direction of the rays, it is possible to obtain a variety of axonometric projections of the same object.

Most often in the construction of drawings, an isometric rectangular projection is used, in which the reduction factor of dimensions is the same in all axes, and the angles between the axonometric coordinate axes are 120 degrees. It is obtained in a parallel way.

Virtually everyone who studied engineering graphics and drawing, had to perform the construction of an axonometric projection. In practice, a wide choice of these drawings is strongly limited by the requirements of low labor intensity and clarity. GOST 2.317-69 recommends the use of axonometric projections that allow good image perception, while having a successful combination of distortion coefficients and simple construction. There are five types: three oblique (frontal, horizontal isometry, frontal dimetry) and two rectangular (dimetry and isometry). Of course, they can not replace the projection drawing, but they can only supplement. The construction of axonometry is very laborious, it is used when the drawing does not give a complete picture of the shape of the image being displayed or the entire object.