1. How to limit the position of the shaft, including radial and axial position, is the first issue to be considered. The general use of double-bearing shaft structure, the radial position of the shaft jointly defined by the two bearings, each bearing radial positioning should be the role of radial or angular contact bearings. Axial position can be limited by two bearings in each direction of the axial displacement can also be limited by a support axial displacement in both directions, in general, different axial positioning can get different operating accuracy. Therefore, the design of the support structure should be based on the accuracy of the operation of the shaft and working conditions, select the specific program of axial positioning. 2. In the case of radial load and axial load at the same time, the bearings are often installed in pairs with angular contact bearings and tapered roller bearings. Angular contact bearings installed in pairs of three arrangements. The two bearing outer ring wide end face relative mounting said back to back mounting. The two supporting forces point outside the supporting span. This arrangement due to the large span of support, when the shaft cantilever steel, the shaft elongation, the outer ring was detached trend, so the shaft will not be stuck, it is more widely used. However, if the preload installation, the amount of preload will be reduced when the shaft is heated. Two bearing outer ring relative to the installation of the narrow face that the face-to-face installation. The force point of the two supports lies within the support span. This arrangement is simple in structure, assembly and disassembly, commissioning are more convenient to use it is also more widely used, mainly for short axis and temperature rise is not high occasions, but be sure to be sure to have spare clearance. Axial clearance should not be too large, over the General Assembly to reduce the operating accuracy of the shaft. When the axial load is large, the need to bear multiple bearings at the same time, often using bearing outer ring width, narrow face relative to the series installed. The bearing force points are on the same side of the bearing so called the same arrangement, also known as series. When using this arrangement should pay attention to structural and manufacturing to ensure that each bearing can be as uniform as possible to bear the load. 3 machine is running, the general temperature of the spindle or drive shaft is higher than the adjacent parts temperature, so the shaft will heat up elongation. In order to maintain the flexibility of the shaft rotation, in the design of the support structure, in order to meet the axial positioning accuracy requirements, but also consider the shaft free heated telescopic requirements. Axial positioning and axial expansion of the corresponding way. 4. Adjust the bearing clearance is to control the operation of the shaft accuracy. Axis axial position adjustment is to meet the special requirements of some meshing transmission. For example, in a worm drive, the worm axis must fall within the mid-plane of the worm gear to ensure proper engagement and therefore require that the worm shaft be able to adjust its position in the axial direction. In a bevel gear drive, the conic cone vertices of the two bevel gears must coincide, thus requiring both bevel gear shafts to be axially adjustable.