How to understand drawings

Drawings are the language used by engineering and technical personnel to communicate. It is difficult for non-professionals to read mechanical drawings. At first glance, it seems to be obvious. However, upon closer inspection, it does not seem so. Something happened. This experience describes how to easily understand mechanical drawings. Mechanical engineering is a rigorous and highly practical subject. As far as drawings are concerned, if there is a point that is unclear, it cannot be used to guide practical applications.

Tools/raw materials

A copy of the drawings

A pair of eyes

A mechanical design manual (set)

Steps/Methods

1

Determine the type of drawing. There are many types of mechanical drawings, including assembly drawings, simplified drawings, schematic drawings, parts drawings, etc. You must first determine what kind of drawing you get. Only then will you know what object the drawing expresses and what aspects it expresses. To what extent.

2

Read object information. Although the drawings will be different for each person and every company, they all follow the national drawing standards. A drawing is made for people to see. If there are too many special places and others cannot see it, it will lose its meaning. . First, look at the object name, number, quantity, material (if any), proportion, unit and other information in the title bar (lower right corner). The location of this information can be found in the relevant parts of the manual.

3

Determine the view. If it is a non-"standard" drawing such as a schematic diagram, there is no strict concept of view. Standard drawings have at least one view. The concept of view comes from the projection of drawing geometry. You can also read the relevant content in the manual for this knowledge. Simply put, according to our country’s drafting standards, an object is called the main view when viewed from the front, and the main view when viewed from the left. It is the left view (placed on the right side of the main view), the top view is called the top view (placed below the main view), and the sectional view and many other view concepts. Reflected in the drawing, the view is just a piece of "thing". There are no dimensions, text, lines, etc. between the blocks to connect them, and there is a blank space in the middle. People with architectural and other viewing abilities will be familiar with these concepts, and they are all universal.

4

Distinguish between the main body and annotations. After determining how many views there are and what they are, we need to distinguish the main body (let’s call it this for now, I invented this word). The main body is the lines that describe the mechanical parts (in the actual two-dimensional world of parts, these are the Lines), which can be distinguished based on the thickness of the line (thin lines are all marking lines). The main lines only have thick solid lines (thickness can be judged by relative comparison, and there are also standard thicknesses in the standard), thick dotted lines and section lines .

5

The actual appearance of the parts is restored by the main body. This is the key point of the view. Everything else can be done by reading books and flipping through manuals. Only this requires accumulation and spatial imagination. If you cannot restore the appearance of the actual parts, you will have that joke about digging a well but building it. A chimney. If you have difficulty when restoring, you can carefully determine what view each view is (including expression methods such as section views), and auxiliary dimensions (for example, R represents radius, and that line is an arc (surface). These annotations are in the manual. Yes, it is relatively simple.

6

You can take a rough look at this and have a general idea. If you are a manufacturer, you can use it. Let’s take a look at it later.

7

The dividing line between outsiders and outsiders. At this point, as long as you have read the drawings and studied the content expressed in the drawings in the mechanical design manual, you are considered qualified. For laymen who can understand drawings, just like after you read a drawing of a house, you know the structure and size of the house. If you don't want to go into details, you can stop here. However, the mechanical drawing information is much more than that. These.

8

Enter mechanical picture recognition.

Mechanical drawings (these are all standard drawings, schematics, etc. without introduction) express the structure, size, material, accuracy, etc. of a part or component or a machine, and all the design data used in the mechanical industry. We have seen the material and structural parts before, and we will talk about other information later. Since almost all the mechanical information is in the drawings, and the mechanical design manual alone has thousands of pages, so I cannot share all my experiences here, only those who are new to the industry. experience.

9

Accuracy. Mechanical dimensions (such as the diameter of a cylinder) are not just a dimension. Whether the tolerance is marked (±0.XX) or the size is not marked, it is a range. This is the concept of mechanical (dimensional) accuracy. Always have it. Because mechanical parts are generally produced in large quantities, precision is required to control the size of each part (they cannot be the same size, there will be errors) within a certain range. Similarly, components also have geometric tolerances (which also exist whether marked or not). Unmarked accuracy (tolerance) is stipulated in national standards. The technical requirements of some drawings will state that accuracy is the soul of mechanical parts. This requires a certain amount of accumulation. You can learn and understand each drawing by referring to the manual. Accuracy information.

10

Process. Simply put, process is how to manufacture (assemble) this part. Although mechanical drawings do not express direct information about the process (process), they do contain the basic process. It is meaningless if a part is designed but cannot be processed. How to process it is something that the designer has considered, and it will also be expressed in the drawings.

Roughness: Roughness determines the usage requirements and also limits the processing method requirements.

Accuracy: For example, the size, position, shape tolerance and roughness requirements of an element (an inner hole for bearings) will imply its processing technology requirements (grinding).

Heat treatment: Heat treatment makes processing feasible and the performance meets the usage requirements.

Surface treatment: Surface treatment is generally proposed in the technical requirements.

In short, the information expressed in the drawings must be read out. This is also the key role of mechanical drawings. Of course, in practice, there will be process writers who will write detailed process (documents) based on the company's actual processing capabilities. ), people who can understand mechanical drawings should be able to clearly understand how to process this thing after restoring the actual parts.

11

Details. To put it simply, most of the drawings have a round sky and a square place (mostly either circles, arcs or right angles). However, in actual processing, due to limitations of tools and other reasons, right angles often have tool tips and bent circles. Arcs, and some arcs are not actual arcs. You must have a general understanding of the actual effects of various processing methods, and you must have a concept of the difference between the "ideal" appearance expressed in the drawings and the "actual" appearance. Of course, these differences This was considered during the design and will not affect its functionality due to differences.

12

Inspection. You must have a general understanding of the use of various measuring tools, testing methods and items. Since mechanical parts have special characteristics, they are either very precise and ordinary steel tape measures and rulers cannot be used as inspection measuring tools, or they are very large ( Very small), and also exceeds the range of traditional internal and external diameter gauges and vernier calipers. Each dimensional requirement and accuracy requirement requires special detection methods. The inspection method is not only the final judgment of whether the parts are qualified or not, but also a necessary process during processing.

END

Notes

The dimension unit of mechanical drawings defaults to millimeters (mm), which will not be marked in the drawings.

There is a ratio in the drawing of drawings, which is the scaling factor of the actual size on the drawing. This ratio cannot be used as the basis for actual measurement (for example, parts with a size of 1:1 are directly measured on the drawing).

Machinery is a multi-disciplinary, comprehensive and practical technology, and mechanical drawings are the language of the machinery industry, so drawings are ever-changing, complex, rigorous, and have practical significance.

Mechanical things are not science, not experiments, and not based on imagination. It is a technology, a real technology.