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The big guy explained the basic knowledge of mechanical drawing (27), the size and number of the assembly drawing of the basic knowledge of mechanical drawing

The basic knowledge of mechanical drawing is particularly important. Only with a solid basic knowledge of mechanical drawing can you further improve your personal skills. For the basic knowledge of mechanical drawing, the editor has brought 26 related articles. Friends who are interested in the basics of mechanical drawing can read it at any time. This article explains the basic knowledge of mechanical drawing, mainly to introduce the size of the assembly drawing and how to code the part number, let’s understand it together.

1. Part number in assembly drawing

(1) The method of editing the part number

1. All parts in the assembly drawing, or manufacturing parts that are not easy to decompose must be programmed with a serial number.

2. In the assembly drawing, only one serial number can be written for a component, and the parts in it are no longer subdivided.

3. In the same assembly drawing, parts and components with the same size and specification should be written with a serial number.

4. The serial numbers of parts and components in the assembly drawing are the same as the serial numbers in the detail column.

(2) Some stipulations in the serial number labeling

1. The composition of the serial number

Mark a whole serial number, including:

(1) Small black dot: In the contour line, as the starting point, if it is not in the contour line, but a thick solid line, it is often an arrow to indicate the position.

(2) Guide line: The guide line is drawn with a thin solid line and should be drawn from the visible outline of the pointed part.

(3) Horizontal line: The horizontal line is drawn with a thin solid line to indicate the numerical position of the serial number.

(4) Numbers: When the serial number is marked on the horizontal line of the guide line, the height of the word is one size larger than the height of the size number marked in the assembly drawing.

2. Arrangement of serial numbers

The serial numbers are neatly arranged horizontally or vertically around the assembly drawing, and the serial numbers can increase clockwise or counterclockwise for easy search.

When it is not possible to continuously program all the required serial numbers in one view, you can continue to program in other views according to the above principles.

3. Other regulations

(1) In the same assembly drawing, the form of the serial number should be the same.

(2) When a small black dot is used in the part indicated by the serial number guide line to indicate that it is unclear (such as a very slender or blackened section), the dot can be replaced by an arrow, and the arrow should point to the outline of the part, as shown in Figure 1. Show.


(3) The guide line should be different from the lines in other views and be parallel to it for easy identification. If necessary, it can be drawn as a polyline, but it can only be bent once, as shown in Figure 2.


(4) There are many guide lines around the view, but they cannot cross each other, as shown in Figure 3.


(5) For a group of standard parts or a group of parts with a clear assembly relationship, a common guideline can be used. The annotation method is shown in Figure 4, but it should be noted that the horizontal lines should be arranged neatly.


Second, the size of the assembly drawing

(1) Performance size

A dimension that represents a performance, specification, or feature of an assembly, sometimes referred to as a gauge dimension. It is often the basis for the design or selection of assemblies. As shown in Figure 5, the piston diameter 36H6/h5 and stroke 24 in the front view of the hand-operated oil pump diagram determine the amount of lubricating oil delivered by the oil pump piston back and forth.


(2) Assembly size

A dimension representing the assembly relationship between the parts of the assembly, including:

1. Matching size

Indicates the size of the fitting properties of the parts, such as 36H6/h5 in the assembly drawing of the hand pressure lubricating oil pump shown in Figure 5, which indicates the fitting properties between the piston hole and the piston, which is a clearance fit.

2. Relative position size

Indicates important relative position dimensions between parts. Dimension 13 in the assembly drawing of the hand-operated oil pump as shown in Figure 5.


(3) Dimensions

Indicates the outline dimensions of the assembly, usually the overall length, overall width, and overall height, which are the dimensions required for the assembly of components during packaging, transportation, and installation.

As shown in Figure 5, the length of the hand-operated oil pump is 230, the height is 160, and the width is 80.


(4) Installation size

The structure and size required for installing components on the foundation or connecting other components must be indicated in the assembly drawing.

As shown in Figure 5, the inclination angle of the installation contact surface in the figure of the hand-operated lubricating oil pump is 5°32′, the positioning size of the installation hole is 70, 35, and the fixed size is 4 × 10 round hole.


(5) Other important dimensions

Important dimensions calculated or determined that cannot be included in the above categories.

As shown in Figure 5, size 68 in the hand-pressed oil pump drawing. In addition, sometimes it is necessary to note the extreme position size of the moving parts, such as 46° in the picture of the hand-pressed lubricating oil pump.


The above types of dimensions are not required to be noted on every assembly drawing, but should be determined according to the specific conditions of the assembly. On some assembly drawings, the same size may have several meanings. As shown in Figure 5, the 36H6/h5 in the hand-operated oil pump diagram is both the specification size and the matching size.

The above is the relevant content of “Basic Knowledge of Mechanical Drawing” brought by this editor. Through this article, I hope that everyone has a certain understanding of the content explained in this article. If you like this article, you may wish to continue to pay attention to our website. The editor will bring more exciting content later. Finally, thank you very much for reading, have a nice day!