# The volume, content and sequence of drawing a general view...

## The volume, content and sequence of drawing a general view

Stages of developing a general view drawing. When drawing a general view, the following works are usually performed in a certain sequence.

Fig. 16.1

Fig. 16.2

Fig. 16.3

1. Acquaintance with the assembly unit: the study of the purpose, design, operation and interaction of the components, as well as the sequence of disassembly and assembly. Usually, they are guided by the passport developed by the department - the diagram of the assembly unit, the description and the specification.

2. Execution of sketches of parts included in the assembly unit, including sketches of some standardized parts. Linking the conjugate dimensions of parts. Shooting sketches of parts is discussed in detail in Chapter 15.

3. Running a general drawing based on sketches. This solves the problems of selecting the main image and the number of images in the general view drawing. Before planning it is useful to carry out by hand the isometry of the assembly unit. An example of planning a general layout is shown in Fig. 16.1. The layout is usually based on the sketch layout of the body part. This step is discussed in more detail below.

An example of drawing a general view is shown in Fig. 16.2, the table to it is shown in Fig. 16.3 (usually filled by hand).

The peculiarity of working on a general view drawing is that students take pictures of the sketches of details only in the classroom. When working on a general drawing, students work out separate ESKD standards, the numbers of which are indicated in the corresponding paragraphs. For the solution of certain constructive questions, it is recommended to use educational-methodical and reference literature.

Introduction to the task. To perform a general view drawing, each student is given an individual task - a variant of the assembly unit with a technical description. Guided by the technical description, it is necessary to understand the purpose of the assembly unit, the principle of operation and the interaction of the main components. Mentally outline the sequence of disassembly and assembly and execute them practically. In this case, it is necessary to carefully study the structural and technical forms of the components.

The execution of the sketches of the parts of the device has its own peculiarities, determined by the design of the connections, and is discussed below in § 16.3. Features of selecting the main image and the number of images - the layout of the drawing, as well as some rules relating to the design of a general view, are discussed in § 16.4.

## Running Thumbnails for a General View

General rules for shooting sketches of parts are discussed in Chapter 15. When shooting sketches of parts for drawing a general view of the assembly unit, special attention is paid to the questions of applying and linking the dimensions of adjacent, mating parts. Chapter 15 considers a system for depositing dimensions mainly from technological considerations (see § 15.5), from technological bases. When shooting the same sketches of parts of assembly units, some dimensions are applied taking into account the interconnection of these parts in the devices and their design features, ie, from constructive considerations, from the design bases. These features are discussed below.

Fig. 16.4

When shooting thumbnails for general drawings, sketches of the assembly units that make up the device are sometimes performed. These assembly units include reinforced products, for example, plastics with metal parts.

As an example in Fig. 16.4, 16.5, 16.6, a - 3 is a set of completed sketches for the vernier (Figure 16.6, b - s only with dimensional lines) a general view of which is shown in Fig. 16.2.

Sketches of assembly units. If the product has assembly units, sketches on them are prepared with sketches of assembly units with specifications that determine their composition. In the learning process, these assembly units are usually permanent joints of parts (or parts and materials) obtained by reinforcement, welding or surfacing, and also all-in-one

Fig. 16.5

joints of parts (materials), which after joining them by soldering, gluing, expanding, pressing and other assembly operations are subjected to additional machining. The parts (metal fittings), which are part of such assembly units, make out individual sketches. For more details on the specification, see § 17.1.

Example . In the one shown in Fig. 16.2 Vernier designs The handle 1 is an assembly unit, which is a reinforced product. A sketch is developed on it - Fig. 16.4, with the specification in Fig. 16.5. The vernier handle consists of an armature - a metal bushing 1 and a material - plastic 2. In the reinforced assembly unit, the material acquires a shape set by a sketch or drawing after pressing (or pouring) into a mold together with fittings. Therefore, on the sketch (drawing) of the reinforced assembly unit, all dimensions defining its shape are applied, except for the dimensions of the reinforcement, and also the dimensions that determine the position of the reinforcement relative to the molded surfaces. In the sketch in Fig. 16.4 all dimensions that define the shape of the plastic part of the handle are marked. The size of 4 mm determines the position of the metal sleeve relative to the end of the handle. A metal bushing is used in the manufacture of a metal-plastic vernier handle as an independent pre-fabricated part. Therefore, a separate sketch is made on it - Fig. 16.6, a, on which are applied

Fig. 16.6

all dimensions required for its manufacture (threaded hole M4 on the sketch of the sleeve is not shown, since it is processed after pressing the handle).

Conjugated and free dimensions. The dimensions of the parts of the assembly units are divided into mates and free. The conjugate dimensions are the dimensions of the interconnected parts, which must be the same. They provide the set position of parts in the assembly unit, the accuracy of its work, the proper conditions for assembly and disassembly, the required interchangeability of parts. After manufacturing the parts, these dimensions must be checked by the quality control or quality controllers.

When shooting sketches from device parts, issues of correct measurement and application of conjugate dimensions are given special attention.

Free dimensions are usually referred to the surfaces of parts that do not come into contact with other parts of the assembly unit and do not significantly affect the operation of the mechanism. However, the values ​​of individual free dimensions of adjacent parts can be interconnected by certain design conditions (the free dimensions of one part are applied in accordance with similar dimensions of adjacent parts). Such dimensions are called free dependent.

Correct application of such interdependent (dependent) free dimensions in the drawing is a prerequisite for ensuring the correct operation of the product, its installation and dismantling. Therefore, when shooting sketches, allocate free dependent dimensions of the parts of the device and verify the correctness of their measurement and application on sketches.

The nature of the relationship between the dimensions of the details of the assembly unit is determined by its design. Let us explain this with examples.

In Fig. 16.7. The valve seat I is pressed into the body 2 for the diameter d whose values ​​for the seat and body are conjugate dimensions. At the same time, the diameters d of the 2 saddles and <7, the bodies are free dependent sizes, since they do not have large requirements for manufacturing flow; it is only necessary that d,> d,. Here, the free dependent dimensions are the sizes I 1 saddle and I 1 holes in the body; For them, the condition/2 & gt; /,.

In Fig. 16.8 shows the screw connection of two parts. The external diameters of the thread d , the screw 3 and the parts/are conjugate (the inner and middle thread diameters are also conjugate dimensions, but they do not indicate the threads in the parts drawings). The outer diameter d , the screw threads and the diameter d, of the hole in the detail 2 are free dependent dimensions, since the hole in the part 2 must be greater than the diameter of the screw.

The conjugated dimensions of two conical surfaces with the same taper are shown on the example of a friction clutch (Figure 16.9). Conjugation of conical surfaces is determined by the size of conjugate dimensions - their conicity 1: a and diameters d ( ko -

Fig. 16.7

Fig. 16.8

Nusality - the ratio of the difference between the diameters of the two sections of the cone and the distance between them). In this case, the diameters d are set in main plane, which is for the outer cone (the left half-coupling of /) by the plane of its larger base. For the inner cone (right half of the coupling 2) the position basic plane is determined by the dimension I from one of the ends of the part.

The conjugated dimensions of two pyramidal surfaces are shown in Fig. 16.10. To transfer torque from the handwheel 1 to the stem 2 of the vacuum valve, their coupling is made in the form of a tetrahedral pyramid. The adjoining dimensions here are the slope La of the landing faces relative to the axis of the rod and the dimensions of the cross-sections of the hole at the end of the handwheel and the rod, defined in the basic plane, i.e., dimensions b of the side of the square (in section A-A). The length/of the landing surface of the rod and the length/of the landing surface of the flywheel are free dependent dimensions with the condition /, & gt;/to ensure that the flywheel is axially tightened on the rod.

Other examples of axial coupled and free dependent sizes are given below (see Figures 16.11, 16.12).

In Fig. 16.11, a, in two variants of installing the 2 roller on the 3 panel of the device are shown: a - the roller rotates on the fixed axes 1; the roller rotates together with the shaft I, on which it is fastened with the nut 4 , the washers 5 and the keys 6. In the first construction (Figure 16.11, a) the dimensions of the/roller and the axis are the conjugate dimensions. The necessary clearance is provided by specially designated tolerances

Fig. 16.9

Fig. 16.10

Fig. 16.11

deviations of these dimensions (they are studied in the course on tolerances, plantings and technical measurements) so that the length of the axis is always somewhat longer than the length of the roller (if the value of the nominal value l for the roller and the axis is equal). The dimensions of the length of the axis and the length of the roller are made with great accuracy. If these dimensions are not properly carried out, the roller may be clamped in the axial direction or, alternatively, an unacceptable axial play (backlash) may occur between the roller and the housing. Correct application of the dimension l of the length on the roller axis from the constructive base - end K is shown in Fig. 16.11, b. In the second construction (Fig. 16.11, c) the roller is clamped to the shaft in the axial direction, which ensures the condition I 1 & lt; I 7. In this case, the sizes I l Hl 7 - are free dependent. The scheme of drawing length dimensions on the shaft from the technological base T in this case is shown in Fig. 16.11, g.

Another example of drawing length dimensions from the technological base T is shown in Fig. 16.12 for the case of a fixed ball bearing on the shaft (only half of the cut is shown conditionally). Free dependent dimensions:/- height of the inner ring of the bearing, A and B - axial dimensions of the shaft (/> BA). The dimensions A and B are plotted from the technological base T.

In Fig. 16.13 shows the handle of the device, the handle 2 of which rotates freely on the axis 1. The pin 3 prevents the handle from sliding off the axis, and the annular groove on the axis allows the handle to rotate freely with the pin around the axis . The size I 7, which determines the position of the groove on the axis, and the size/"determining the position of the pin in the handle, are free dependent dimensions ( I 2>). In this construction there are other - both conjugate (diameter d t ), and free dependent ( d 7 and d , d, & gt; d 2 ) are the sizes of the diameters of the axle and the handle.

The dimensions that define the position of the axes of the holes of the two parts connected by screws, bolts or pins are also conjugated (see Figures 16.14, 16.15).

Fig. 16.12

Fig. 16.13

Fig. 16.14

Fig. 16.15

In Fig. 16.14 The mating size/determines the position of the axes of the screw holes in the slide bearing/and in the device housing 2.

In the construction in Fig. 16.15 for details 1 and 2 the diameter of the axes of the holes for the fasteners is conjugate. The angular dimension is also the angular dimension - the value of the angle a, which determines the position of the keyways in both parts relative to the axes of their fixing holes.

The above examples, of course, do not exhaust the whole variety of conjugate and free dependent sizes on the parts drawings. However, when surveying sketches, you need to analyze the design of the assembly units and pay special attention to the correctness of measurement and application of the specified dimensions.

After capturing the sketches from the parts, all conjugate and dependent dimensions are emphasized with a red pencil, checking the correctness of their measurement and application and, if necessary, correcting by repeated measurement.

Album thumbnails. A set of sketches for an assembly unit is dubbed into a cover of thick paper. The front side of the cover is made according to the model adopted at the department.

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