Do you know the standard for selecting the dimension datum of shaft sleeve parts
According to the use basis: 1. Design basis. The point, line and surface used to determine the position of the part in the 6014 cross shaft bushing machine are called design datum. 2. Process benchmark. The selected datum for processing, measuring and inspection of parts. According to the form of datum: ① datum point, a point on the part surface. ② Datum line, the axis of the turning surface on the part. ③ A certain surface on the part, including the main assembly surface and supporting surface on the part; Main machining surfaces (locating surfaces, contact surfaces) on parts; The symmetry plane of the part (symmetrical in a certain direction).
2、 Selection of datum
In order to reduce errors and ensure the design requirements of parts, it is better to make the design reference coincide with the process reference when selecting the reference of stainless steel shaft sleeve. If it is impossible to coincide, the functional dimensions of the parts shall be marked from the design datum, and the unimportant dimensions shall be marked from the process datum or according to the shape analysis method. When the stainless steel welding sleeve of the part is complex, it is often not enough to select only one datum in one direction, and some datum should be added. Among them, the one that plays the main role is called the primary benchmark, and the one that plays the auxiliary role is called the auxiliary benchmark. There should be connection dimensions between the main datum and the auxiliary datum.
3、 Selection standard of dimension datum for shaft sleeve parts
1. Selection of radial dimension datum
According to the structural characteristics of this part, the shape is relatively simple and regular, and most of them are composed of cylindrical revolving bodies of different sizes but coaxial. Steps formed by unequal diameters can be used for axial positioning of parts installed on the shaft. Due to the needs of design, processing and assembly processes, such parts often have chamfers, fillets, threads, thread undercuts, grinding wheel overtravel grooves, keyways, etc. The shaft sleeve shall be processed accurately. Most of the machining (rough machining, semi finishing) shall be performed on the lathe, and a few of the machining (finishing) shall be performed on the grinder or other machine tools. Lay the axis horizontally on the main view according to the processing position, and select the axis of the axis according to the radial dimension datum, so as to unify the design requirements and the process datum during processing.
2. Datum selection for axial dimensions
Since there are many dimensions in the length direction, which end face is selected as the main datum in the length direction. The main function of the bearing on the shaft is to support the mechanical rotating body, which is used to reduce the friction coefficient during the power transmission process and maintain the fixed position of the shaft center. Therefore, its performance in all aspects directly affects the transmission of power and torque of the shaft, so the dimensional accuracy of the connecting end faces of the shaft and bearing is required to be high.
3. Look at the pictures and use analogy; Multi practice and contrast method;
In order to properly point out the dimensional datum in all directions for the given drawing of shaft sleeve parts, it is necessary to understand the characteristics and functions of the structural shapes of the components, their mutual positions in the machine and their functions. In fact, we should pay more attention to the drawing "analogy". Machining is a highly empirical work. In actual production practice, we should analyze and compare the original design ideas and add new design ideas. Rely on the "comparison method" to design, and look at the drawings of the same type. How these drawings deal with this problem is helpful to understand the problem of dimension datum selection.
The selection of part datum is determined by the processing technology or on-site processing conditions of the part. The shaft sleeve processing shall be targeted at Tihao. The shaft sleeve parts are rotary parts. Considering that most of its processing (rough machining, semi finishing) is carried out on the lathe, the main view generally selects the horizontal axis for projection. When selecting the datum, the axis of the part is often used as the radial dimension datum, so that the design requirements and the process datum during processing (when the shaft parts are processed on the lathe, the central hole of the shaft is held by the tip at both ends) are unified, while the main datum in the length direction often selects the important end face (the face with the highest processing accuracy), contact face (shaft shoulder) or important processing surface, Other benchmarks set for ease of processing and measurement are auxiliary benchmarks.