As people engaged in machining, the reasonable design of the product machining tolerance is conducive to the processing of parts and quality assurance, machining tolerances and machining allowances between the correlation is also often misunderstood, resulting in the design of the machining tolerance is unreasonable, unable to meet the requirements of the parts of the drawing, and ultimately scrapped.

The design of mechanical parts, first of all, from the assembly point of view, in accordance with the fit of the parts to give the corresponding tolerance standards, while the parts in the machining enterprise, it should be considered that the processing technology and surface treatment to design the corresponding machining tolerances. In the parts of the pre-opening rough, the general tolerance is relatively large, subject to allowances, in the finishing process, the type of surface treatment should be considered, according to the surface treatment of the size of the change in the design of finishing dimensional tolerances to meet the accuracy of the product after finishing, many inexperienced process engineers, it is often easy to be in the finishing process in accordance with the requirements of the customer's drawings labeled dimensional tolerance control, ignoring the impact of surface treatment on the dimensional control, and the surface treatment of the surface treatment. Many inexperienced process engineers often tend to control the dimensional tolerance according to the customer's drawing labeling requirements in the finishing process, ignoring the dimensional impact of the surface treatment, which ultimately leads to the parts tolerance can not be guaranteed, rework or scrap.

Machining tolerances must be combined with the production process and surface treatment to set, if it involves the assembly process, it should also consider the size of the assembly changes, choose what kind of assembly, different assembly for the size of the change is different, these need to be based on the actual changes or experience to determine the surface treatment of the same way, the same way, different surface treatment companies, the pH of the tank fluid is not the same as the actual changes. The same surface treatment method, different surface treatment enterprises, different pH of the bath solution, the actual change is also different.