The rules for the image of objects (products, structures and their constituent elements) in the drawings of all industries and construction are established by GOST 2.305 - 68.

Images of objects should be performed using the method of rectangular (orthogonal) projection onto a plane. In this case, the object is placed between the observer and the corresponding projection plane. Attention should be paid to the difference between an image and a projection of an object. Not every image is a projection of an object. There is a one-to-one point correspondence between the object and its projection, which consists in the fact that each point of the object corresponds to a certain point on the projection and vice versa.
When constructing images of objects, the standard allows the use of conventions and simplifications, as a result of which the indicated correspondence is violated. Therefore, the figures obtained when projecting an object are called not projections, but images. The faces of a hollow cube are taken as the main projection planes, into which an object is mentally placed and projected onto the inner surfaces of the faces. The faces are aligned with the plane, as shown in Fig. 1.

Figure: 1 Types

The image on the frontal plane is taken as the main one in the drawing. The object is positioned relative to the frontal plane of the projections so that the image on it gives the most complete picture of the shape and size of the object. Images in the drawing, depending on their content, are divided into views, sections, sections.
View - the image of the visible part of the object's surface facing the observer. To reduce the number of images, it is allowed to show the necessary invisible parts of the surface in views using dashed lines. However, it should be borne in mind that the presence of a large number of dashed lines makes it difficult to read the drawing, so their use should be limited.

The types are divided into basic, local and additional.
Main types - images obtained on the main projection planes - cube faces (Fig. 1):

1 - front view (main view);

2 - top view;

3 - left view;

4 - right side view;

5 - bottom view;

6 is a rear view.

The names of the views in the drawings are not labeled if they are located as shown in Fig. 1, i.e. in projection communication. If the views from above, to the left and to the right are not in projection connection with the main image, then they are marked on the drawing with an inscription of type "A". The direction of gaze is indicated by an arrow denoted by a capital letter of the Russian alphabet.

When there is no image on which the direction of gaze can be shown, the name of the species is inscribed.

Local view - an image of a separate limited area of \u200b\u200bthe surface of an object on one of the main projection planes. The local view can be placed on any free place of the drawing, marking it with an inscription of the type "A", and an arrow indicating the direction of the gaze should be placed at the associated image of the object, with the corresponding letter designation (Fig. 2).

Figure: 2. Complementary and local views.

The local view can be limited by the cliff line, as small as possible, or not limited (Fig. 2).

Additional types - images obtained on planes that are not parallel to the main projection planes. They are used in cases where any part of the object cannot be shown in the main views without distorting the shape and size. The additional view is marked on the drawing with an inscription of type "A" (Fig. 2), and an arrow with the corresponding letter designation (arrow A, Fig. 2) is placed on the object associated with the additional view of the image, indicating the direction of gaze.

When the additional view is located in direct projection connection with the corresponding image, the arrow and the inscription above the view are not applied (Fig. 2). The secondary view can be rotated while maintaining the position taken for this item in the main image. In this case, the sign "rotated" is added to the inscription "A" (Fig. 2).

Basic, local and additional views serve to depict the shape of the outer surfaces of the object. Their successful combination allows you to avoid dashed lines or reduce their number to a minimum.

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In drawing, three main types of lines are used (solid, dashed and dash-dotted) of various thicknesses (Fig. 76).

In Figure 75, the thickness of each line in millimeters is indicated by numbers.

Let's take a closer look at each of the line types and their main uses.

1. Solid contour line is considered the baseline of the drawing. Its thickness is chosen depending on the size of the drawing, its complexity and purpose. The thickness of the contour line is indicated by the letter b and can take values \u200b\u200bfrom 0.4 to 1.5 mm (Fig. 77).

The thickness of other lines in the drawing is determined by the line width of the visible outline. In the same drawing, all lines of the same name must be of the same thickness.

2. Dashed line of invisible path used to draw the outlines of internal planes and lines hidden from the observer, as well as to represent the thread and the circumference of the depressions of the gears (Fig. 78).

The thickness of the line of the invisible contour should be two to three times less than the thickness of the line of the visible contour. The length of the strokes is four times the distance between strokes. Most often, the stroke length is 4–6 mm, and the distance between the strokes is 1.1–1.5 mm. Typically, stroke length decreases with line thickness. In small drawings, the stroke length can be reduced to 2 mm.

3. Break lines, cliff or notch are divided into three main types (Fig. 79):

1) the wavy line of the break is a line of the same thickness as the line of the invisible contour. It is carried out by hand;

2) the dash-dotted line has the same thickness as the wavy one. The stroke length is approximately 10.1-12 mm, and the distance between the strokes is 3 mm. In small drawings, the stroke length may be shorter;

3) the break line can also be drawn in the form of a thin line with rectilinear zigzags. Such lines are used when constructing long break lines.

4. Thin solid line. Its thickness is four times less than the thickness of the contour line, and it is often used. It is used to carry out extension and dimension lines, carry out shading and all kinds of auxiliary lines that are necessary in the process of any construction or explain it (Fig. 80).

5. Centerlines and Centerlines (fig. 81). They are thin dash-dotted lines with relatively long strokes. The striae are approximately 20–25 mm long. The distance between the strokes is approximately 3 mm. In small drawings, the stroke length may be shorter. This dash-and-dot line is used to draw both the initial circle, and the generatrix of the initial cylinder and the initial cone, and for gears.

6. Dash-dotted line with two dots(Fig. 82) is used for the outline of the dimensions, the contours of the mechanism in its extreme or intermediate position and the contour of the boundary part, which is of secondary importance. These lines have the same thickness and length of strokes as regular dash-and-dot lines used as center and center lines.

7. Overlaid projection contour line used to depict parts that fall away during cuts or are in front of the part being drawn, as well as for variants of the part and for drawing the contour of the workpiece drawn on the part drawing. The length of the strokes, depending on the size of the projection, should be 4–8 mm.

8. Drawing frame line, stamp outline, table graphetc. are drawn with a solid line. It can be thinner than the outline line. When choosing the thickness of such lines, it is necessary to strive to ensure that the drawing has a beautifully designed appearance (Fig. 83).

Consider lines to indicate a flat surface. When surfaces of revolution alternate with flat faces (Figure 84), the presence of these flat faces should be shaded. To do this, thin diagonals of each flat face are applied on their projections, which is a conventional designation in the drawing of a flat surface.

For tracing various lines (axial, center, dimensional, extension, section, section, boundary part contour, superimposed section contour, mechanism contours in their extreme or intermediate positions and outline outline, for projection axes, plane traces and characteristic points construction lines) in addition to black, there are also other colors.

Six types are used in drawing, which are shown in Figure 85. The figure shows the projection of the letter "L".

The three projections studied in descriptive geometry form the following three views: frontal projection, which is the main view, or frontal view; horizontal projection, which is a top view (plan); profile projection, which is a left view of the depicted object.

The views are located in the drawing as shown in Figure 85, i.e.:

1) the top view is usually located under the main view;

2) left view - to the right of the main view;

3) view to the right - to the left of the main view;

4) bottom view - above the main view;

5) rear view - to the right of the left view.

All considered projections of an object are usually obtained using data of two types. Figure 86 shows the construction of a triangular pyramid according to these two projections of its three more projections (all except the rear view).

Figure 86 shows auxiliary construction lines. The construction of the necessary projections is similar to the construction of a profile projection from the given horizontal and frontal projections of the object.

When depicting objects that are projected in the form of a symmetrical figure, you can draw slightly more than half of it instead of the whole view. In this case, the projection from the unfinished side is limited by a wavy line, which is two to three times thinner than the contour line.

In some cases, deviations from the rules for constructing projections are allowed. Among these cases, the following can be distinguished: partial views and views located without a projection connection with other views.

Let's consider these cases.

Partial projections. Figure 87 shows a pipe elbow with three flanges.

The main view does not completely determine its shape. Added two partial projections. One of them looks like a flange when viewed from below. In this case, the bottom view is located under the main view so that both flange projections are closer to each other. The second partial projection (to the left of the main view) shows the shape of the inclined flange when viewed perpendicular to its plane.

In this case, it is impractical to fully depict a top or bottom view, since in this case the shape of the inclined flange would be depicted distorted, which would only complicate the drawing, without showing its essence.

Disruption of projection communication. If one of the views has to be located outside the direct projection connection with the main view, or if it is separated from the main view by other images, then you need to either indicate the name of this view, or make special instructions with an arrow and an inscription, for example, "View along arrow A" (Fig. 87 ). If the view is located on a separate sheet, then its name must be inscribed.

The position of bodies in space, shape and size are usually determined by a small number of appropriately selected points.

If, when depicting a projection of a body, pay attention not to its individual points, but to the construction of only contour lines, then some difficulties and ambiguities are possible.

This can be seen from the example.

Consider a rectangular parallelepiped. Its faces are located parallel to the projection planes (Fig. 88).

In this case, one face in full size will be projected onto each of the planes. This position of the body relative to the projection planes facilitates its manufacture according to the drawing.

If you put letters at the vertices of the parallelepiped, then two projections will already define it (Fig. 89).

If you do not put letters at the vertices of the parallelepiped, then only three projections will determine its shape (Fig. 89). To make sure of this, let's draw two of these projections (frontal and profile) (Fig. 90) and try to build a third - horizontal.

Analyzing these two projections, one can imagine not one, but several different projections of the horizontal edge. Therefore, in addition to the original rectangular parallelepiped, several more bodies will have these two projections and differ only in the third.

The idea of \u200b\u200ba product is associated with the study of its shape. The shape is determined by the surfaces bounding the product. To set the shape of the product on the drawing means to build projection images of a set of points and lines that determine the shape of the product and the projection of its contour lines. The image of the product in the drawing is carried out using the method of parallel rectangular projection. For axonometric projections, in addition to rectangular, oblique projection is also used.

View- image of the visible object surface facing the observer (GOST 2.305-68). If it is necessary to explain the drawing, then it is allowed to indicate the invisible contour of the object in the view with dashed lines, which allows to reduce the number of views.

Types are subdivided into the main, additional and local.

Main viewIs a view obtained by projecting an object onto six main projection planes. As the main projection planes, six faces of a hollow cube are taken, inside which an object is placed, and it is projected onto the inner surfaces of the cube (Fig. 2.1).

Figure: 2.1 - Formation of basic views and projections

The image on the frontal plane of projections is taken as the main one in the drawing. The object is positioned relative to the frontal plane of the projections so that the image on it gives the most complete picture of the shape and size of the object.

The following names of the species obtained on the main projection planes are established (Fig.2.1): 1 - front view (main view); 2 – view from above; 3 – left view; 4 - right view; 5 – bottom view; 6 – back view.

When making a drawing of a product, the number of types must be taken as small as possible, but providing a complete picture of the subject. Views must be in a projection link.

Additional viewIs a view obtained by projecting an object onto an additional projection plane that is not parallel to any of the main projection planes.

If the views from above, left, right, below, behind are not in direct (direct) projection connection with the main view, then the direction of view is indicated by an arrow, indicated by a capital letter, and an inscription is made over the view by type AND (fig. 2.2).

In contrast to the additional view, a local view is used for the image in the drawing of a separate, limited place of the surface of an object, which allows you to identify the shape and dimensions of a certain element of the object, for example, the shape of an edge, hole, groove, etc. on a free field of the drawing with an inscription of type D (see Fig. 2.2).

Local View

Additional View

Figure: 2.2 - Local and additional species

In cases where it is impossible to show small elements of an object with all the details on the main image, remote elements are used.

Remote elementan additional separate image (usually enlarged) of any part of an object that requires graphic and other explanations in terms of shape, size and other data is called. The detail may contain details not indicated in the corresponding image, and may differ from it in content (for example, the image may be a view, and the detail may be a section).

When using a detail, the corresponding place is marked in the view, section or section with a closed solid thin line - a circle, rectangle, etc. with the designation of the extension element on the shelf of the leader line with the letter of the Russian alphabet. For a detail, you should specify the letter and scale by type, as shown in Fig. 2.3. The remote element is placed as close as possible to the corresponding place on the image of the object.

Figure: 2.3 - Image of the detail

5.1. View arrangement rules... To fully identify the shape of objects in drawing, various images are used: types, sections, cuts. First, you will explore the species.

Viewis an image of the visible part of the object's surface facing the observer. To reduce the number of images, it is allowed to show the necessary invisible parts of the object surface using dashed lines in views. And the difference from projections in views, some conventions and simplifications apply. You will study them later.

The image obtained on the frontal projection plane is called front view... This image is taken in the drawing as the main thing... Therefore, this type is also called the main one. When making a drawing, the object must be positioned relative to the frontal plane of the projections so that the main view gives the most complete picture of the shape and size of the object.

The image on the horizontal projection plane is called top view.

The image on the profile plane of the projections is called left side view.

Along with the front, top and left views, right, bottom, and back views can be used to depict an object (all of them are called basic). However, the number of views in the drawing should be the smallest, but sufficient to fully reveal the shape and size of the object. To reduce the number of views on them, it is allowed to show, if necessary, the invisible parts of the object's surface with dashed lines. For the same purpose, various conventions, signs and inscriptions established by the standard are used.

Figure: 52. Three types of parts

Figure 52 shows three views of the part, a visual representation of which is shown in Figure 53. The main view is the front view. Below it is the top view, to the right of the main view, and at the same height - the left view. The cut in the rectangular part is invisible in the top view, so it is shown with a dashed line.

Figure: 53. Visual representation of a part

5.2. Local species... In some cases, in a drawing, instead of a full view, you can apply a part of it. This simplifies the construction of the image of the subject.

The image of a separate, limited place on the surface of an object is called local view... It is used in that case. when it is required to show the shape and dimensions of individual elements of the part (flange, keyway, etc.).

The local view can be limited by a clipping line, an axis of symmetry, etc. It can be marked on the drawing and a caption. Place the local view on a free field of the drawing or in a projection connection with other images. At school, you will consider local views located only in a projection connection (Fig. 54).

Figure: 54. Local views located in the projection link

The use of a local view allows you to reduce the amount of graphic work, save space in the drawing field.

1. Give a definition of the species.
2. How are views arranged in a drawing?
3. Which species is called the main one and why?
4. What species is called local? What is it used for? What does the topical form give?

Figure: 56. Exercise assignment

Sketch the data in Figure 56 into the workbook, and the drawings and supplement them with the image of the second box.

Directions for work... If you find it difficult to solve the problem, make the models from the boxes, as shown in Figure 56, and compare the drawings of the models you made with their visual images. Make yourself one or two more models of two or three matchboxes and complete their drawings.

Practical work number 3
Modeling from a drawing

Figure: 58. Tasks for practical work No. 3

Directions for work... Modeling is the process of making a model of an object from a drawing. You have already done this in labor lessons. Before you start modeling, you need to prepare the necessary material: cardboard, wire.

To make a cardboard model, first cut out its blank. Determine the dimensions of the workpiece according to the image of the part (see Fig. 58). Mark (outline) the cutouts. Cut them along the outlined outline. Remove the cut parts and bend the model according to the drawing. To prevent the cardboard from straightening after bending, draw a line from the outside with a sharp object in the place of bending.

A soft wire of arbitrary length must be used for modeling.

Building views begins with a mental choice of the position of the part in front of the projection planes. Then choose the number of types necessary and sufficient to identify the shape of the part, as well as the method of their construction.

The choice of the position of the part in the system of projection planes depends on its working position, manufacturing method in production, shape. For example, if a part is made on a lathe, then its axis of rotation should be horizontal in the drawing.

Drawing views can be performed in various ways. Let's consider some of them.

Construction of views based on the sequential drawing of geometric bodies that make up the shape of an object. In order to complete a drawing in this way, it is necessary to mentally divide the part into its constituent simple geometric bodies, finding out how they are located relative to each other. Then you need to select the main view of the part and the number of images that allow you to understand its shape and sequentially depict one geometric body after another until the shape of the object is fully displayed. It is necessary to observe the dimensions of the form and correctly orient its elements relative to each other (Table 8).

The construction of views on the basis of element-by-element drawing of geometric bodies that make up the shape of an object is carried out using the methods of removal and increment.

When drawing a geometric body using the removal technique, the shape of the workpiece is successively changed in the drawing by removing volumes similar to the techniques for processing it by turning, drilling, milling, etc.

When drawing a geometric body using the increment technique, the volumes of the product elements complement each other, increment.

8. Element-wise drawing of geometric bodies that make up the shape of an object

Construction of views using a constant direct drawing (external coordination method). A constant straight line of a drawing is a line that is drawn from the center of coordinates (point O) down to the right at an angle of 45 ° (Fig. 86).

The object is mentally placed in a system of projection planes. The axes of the projection planes are taken as the coordinate axes. The projection communication between the top view and the left view is carried out using projection communication lines, which are drawn up to the intersection with a constant straight line of the drawing and are built at an angle of 90 ° to each other.

The constant straight line of the drawing, as a rule, is used in those cases when it is necessary to build a third type of part from two given views (see Fig. 86). Having re-drawn two types of parts, build a constant straight line of the drawing and draw lines of projection communication parallel to the OX axis until it intersects with the constant straight line of the drawing, and then parallel to the OZ axis.

The considered construction method is called the external coordination method, since the object is fixed in space relative to the axes of the projection planes, which are located outside the depicted object.

(If the projection axes are not shown in the drawing and it is necessary to perform a third view of the part, then you can build a constant line of the drawing anywhere on the right side of the top view.)

Building views using internal object coordination. Internal coordination consists in the mental introduction of additional coordinate axes tied to the projected object.

Figure: 86. Construction of the third projection on two given using a constant straight drawing

Figure: 87. Building views by means of internal coordination of an object