How To Understand Mechanical Drawings?

How to understand mechanical drawings?

Where to start to quickly grasp key information is a problem you will face after getting a part drawing. It is directly related to whether subsequent production can proceed smoothly, and workers in every link must understand it accurately.

Maximum overall dimensions on the drawing

The first is the length, width and height dimensions marked on the part drawing. This is the primary information. Then, based on these data, the cutting workers must select blank materials of appropriate specifications from the inventory. For example, whether to choose round steel with a diameter of 100 mm or round steel with a diameter of 120 mm, which directly determines the utilization rate of raw materials.

Machining workers care about whether the machine tool table can accommodate parts. For a shaft part with a length of more than two meters, if it is placed on a CNC lathe with a stroke of only 1.8 meters, it will be impossible to complete the processing. Heat treatment workers also have to check the effective size of their own furnace to ensure that the parts can be put in for quenching or tempering.

Clear identification of part materials

On the drawings, the materials used in the parts will be clearly stated, such as 45 steel, 6061 aluminum alloy or 304 stainless steel. Job shops select tools based on the material’s characteristics. For processing stainless steel, wear-resistant carbide blades are needed. However, for processing aluminum alloys, high-speed steel tools can be used. How to read mechanical drawings? , and must be matched with a larger cutting speed.

When doing assembly, the characteristics of the material are also very important. When assembling soft copper parts, if excessive torque or inappropriate tools are used, it is extremely easy to cause the threads to slip or the parts to deform. On the contrary, when assembling high-strength alloy steel parts, sufficient preload force is required to ensure reliable connection.

Detailed interpretation of technical requirements

In the technical requirements section, all the key instructions given by the designer for the manufacturing process are gathered. For example, it is clearly marked as “quenching and tempering to HRC28 – 32”. This means that after the parts are rough-machined, they must be quenched and high-temperature tempered to obtain comprehensive mechanical properties.

This part can also cover geometric tolerances, surface roughness, and specific specifications such as unmarked chamfers, such as “all sharp edge chamfers C0.5”, which prompts the operator to perform unified corner processing during processing to prevent scratches and meet safety requirements. If any of these are ignored, it is very likely to cause batch quality problems.

Dimensional tolerances and fit relationships

Generally speaking, the dimensions on the drawing are not isolated numbers, but have a tolerance range, such as φ50±0.01. This clearly defines the precise manufacturing range of the part, and also determines how it fits with other parts, whether it is a clearance fit, a transition fit, or an interference fit.

For example, there is a situation where a shaft is matched with the inner hole of a bearing. If the drawing mark shows an interference fit, then the hot fitting or press-in process needs to be used during assembly. If the machining behavior is incorrectly carried out according to the clearance fit, it will cause the bearing to slip during operation, thus causing the entire equipment to lose effectiveness.

Surface treatment and special technology

According to the requirements of technical regulations, surface treatment methods are often specified, such as “galvanizing”, “blue”, or “spray coating”. This will not only affect the surface appearance and corrosion resistance, but may also cause the final dimensions of the part to change. Because the electroplated layer will thicken the dimensions, for precision parts, machining drawings need to reserve a margin for the coating in advance when processing.

Requirements for special processes, such as welding, casting flaw detection, dynamic balancing testing, etc., will also be explained here. There is a high-speed rotating fan impeller. If the dynamic balance requirements are ignored, severe vibration will occur during operation, which will cause safety hazards.

Views and sections express intent

A complete drawing uses multiple views of the machining drawing , including the front view, top view, left view, and cross-sectional view to show the parts three-dimensionally. The cross-sectional view can clearly show the internal hole structure, rib thickness and other details that cannot be directly observed from the outside.

People who are proficient in reading pictures can quickly convert two-dimensional machining drawings into three-dimensional solid shapes, and understand the processing sequence of each feature. For example, if you see a blind hole inside with the help of a cross-sectional view, you must drill holes before processing the external features.

After reading these, has your understanding of part drawings become clearer? In actual work, in which part of the drawing are you most likely to misunderstand or miss details? You can come to the comment area to share your experience. If you find it useful, please like it to show your support!