1. Definition of part tolerances Part
tolerance refers to the allowable range of changes in the size of the part, that is, under certain accuracy requirements, the size of the part is allowed to have a certain range of change. Tolerances are usually divided into basic tolerances, general tolerances and limited tolerances. Different types of tolerances are suitable for different parts.
2. Common tolerance types and scope of application
2.1 Datum tolerance Datum tolerances are often used to ensure properties such as isometric, symmetry, flatness, and roundness of a part. Its range is IT01~IT16, where IT is the code name of the international machinery manufacturing standard, and the number indicates the size of the tolerance value. This tolerance applies to parts such as shafts, pins, threads, etc. that are smaller in diameter or length.
2.2 General tolerances General tolerances have a wider range than datum tolerances and generally apply to most parts, such as straight lines, angles, surface roughness and other characteristics. In international standards, general tolerance is usually represented by the letter T, and its range is IT01~IT18. In addition, there are some special general tolerance types, such as cylindricity tolerance, flatness tolerance, verticality tolerance, etc.
2. 3 Limiting tolerances Limit tolerances include clamping tolerances and interference tolerances. Clamping tolerance is usually used for mating parts, and its range is H7~H13; interference tolerance is often used for connecting parts, and parts that need to be tightened during disassembly and installation, its range is P5~P11.
3. Select the appropriate tolerance range
When selecting a tolerance range, consider the specific application of the part and the environment in which it will be used. If the parts require high-precision processing, such as precision equipment or high-precision measuring instruments, the datum tolerance should be selected to ensure the stability and accuracy of the parts. For some general application parts, such as machine tools, vehicle manufacturing, etc., general tolerances can meet the requirements; for connecting parts that need to be disassembled and installed, interference tolerances are more appropriate. It is worth noting that during part processing, the selection of the tolerance range may affect the cost and manufacturing cycle of the part. Too strict tolerance selection will increase manufacturing difficulty and cost, while too loose tolerance will affect the reliability and performance of the part.
4. Summary
Part tolerances are an inevitable part of the manufacturing process and can effectively control the variation range of part dimensions to ensure the accuracy and quality of the parts. When selecting the tolerance range, it is necessary to select the appropriate tolerance type and range based on the specific application and working environment of the part.
