Thread Content
The amount of variation in size allowed by the tolerance is called dimensional tolerance, or tolerance for short. The tolerance of the hole is represented by Th and the tolerance of the shaft is represented by T s. Tolerance is an absolute value, while deviation is an algebraic value. Tolerances and deviations cannot be confused. Tolerance is a value that is not equal to zero and has no positive or negative sign. therefore, * It is inappropriate to conventionally say "zero tolerance", "positive tolerance", and "negative tolerance". Machining accuracy refers to the degree of compliance between the actual geometric parameters (size, shape and position) of the part after processing and the ideal geometric parameters. Accuracy that is too high or too low is unreasonable. Economic accuracy of machined parts is based on tempered ferrous metal materials: The dimensional accuracy of rough turning is IT8~IT10, and the dimensional accuracy of finishing turning is IT7~IT8. The surface roughness of turning processing is Ra1.6. The surface roughness of non-ferrous metal turning is increased by 0.5 to 1 level. The dimensional accuracy of economical precision rough milling of milled parts is IT11~IT13, and the dimensional accuracy of fine milling is IT8~IT11. The surface roughness of milling is Ra3.2. The surface roughness of non-ferrous metal milling is increased by 0.5 to 1 level. The economic precision of the clamped parts is 0.2mm to 0.3mm, and the surface roughness is Ra3.2. The surface roughness of the reamed hole is Ra1.6. The dimensional accuracy of economical precision grinding of grinding parts is IT6~IT7. The grinding surface roughness is Ra0.4~0.8. The surface roughness of surface grinding and inner hole grinding is 0.5 levels lower than that of cylindrical grinding. Tolerance = 1 upper deviation - lower deviation 1 (that is, the absolute value of the upper deviation - the lower deviation), which is also equal to the absolute value of the maximum limit size minus the minimum limit size. For example, let me give a simple example. You will understand that the design size is 100 diameter, the upper deviation allowable range is +0.010, and the lower deviation allowable range is -0.005, then its maximum limit size is 100.1, and the minimum limit size is 99.995. The tolerance is +0.010-(-0.005)=0.015. The processing accuracy refers to the degree of compliance between the actual geometric parameters (size, shape and position) of the part after processing and the ideal geometric parameters. In the design of parts, the amount of variation in the size of the part that is allowed is called a tolerance. Tolerance is represented by uppercase letters for the axis. Tolerance is represented by lowercase letters for the axis. The number following the letter is the accuracy level. The accuracy level of each letter is different, but most of them include level 5, level 6 and level 7. The larger the number, the greater the allowable variation in size, and the less precise it is. The marking method is: basic size + letter + accuracy level. If it is a circle, add Φ in front of it. 21 of the 26 English letters are used in the tolerance. I forgot which five are not included. If it is simply expressed by numbers, such as ±0.03, it is called the limit deviation. You can also not mark the tolerance or limit deviation, then it will be based on the allowable error specified in the data. The difference is used to determine whether the workpiece is qualified. This is called free tolerance. For parts with matching, in order to meet the requirements of matching and replacement of spare parts, the difference between its actual size and nominal size will be given, including upper and lower deviations. The sum of the absolute values of the upper and lower deviations is the dimensional tolerance. There are also geometric tolerances, and shape tolerances include shape: roundness, flatness, etc. Position tolerance includes coaxiality, verticality, etc.