How to define the position of the axis, including the radial and axial positions, is the first problem to be considered.In general, the shaft adopts double support structure, the radial position of the shaft is limited by two supports, and each support should have radial orientation of the centripetal or angular contact bearings.The axial displacement of one direction can be limited by two supports, and the axial displacement of two directions can be limited by one support. In general, different axial positioning methods can obtain different operating accuracy.Therefore, the concrete scheme of axial orientation should be selected according to the operating accuracy and working conditions of the shaft when designing the supporting structure. 

Under the condition of bearing radial load and axial load at the same time, angular contact bearing and tapered roller bearing are usually installed in pairs.Angular contact bearings are arranged in pairs in three ways.Two bearings outer ring wide end face relative installation said back to back installation.The points of action of the two supporting forces fall out of the supporting span.This arrangement because the support span is big, when the shaft cantilever steel is good, when the shaft is heated elongation, the inner and outer rings show the trend of detachable, thus the shaft will not be stuck, so it is widely used.However, if the pre-tightening installation is used, the pre-tightening amount will be reduced when the shaft is heated.Two bearings outer ring narrow end face relative installation said face - to - face installation.The two supporting force points fall within the supporting span.This arrangement is simple in structure, convenient in installation and disassembly and debugging, so it is widely used. It is mainly used in short shaft and low temperature rise, but it must be noted that there must be spare clearance.Axial clearance should not be too large, too much will reduce the operating accuracy of the shaft.When the axial load is large and multiple bearings are required to bear it at the same time, the series installation method with a wide outer ring and a narrow surface is usually adopted.Each bearing force action point falls on the same side of the bearing, so it is said to be arranged in the same direction, also known as series.In this arrangement, attention should be paid to the structure and manufacture to ensure that each bearing can bear the load as evenly as possible. 

Machine in operation, the temperature of the general spindle or drive shaft is higher than the temperature of the adjacent parts, so the shaft will heat up elongation.In order to maintain the flexibility of shaft rotation, in the design of support structure, while meeting the requirement of axial positioning accuracy, the requirement of free expansion of shaft under heat should also be considered.There is a correspondence between axial positioning and axial scaling. 

The clearance of the bearing is adjusted to control the running accuracy of the shaft.The axial position of the shaft is adjusted to meet the special requirements of some meshing drives.For example, in the worm drive, the worm axis must fall in the middle plane of the worm wheel to ensure that it meshes correctly, so the worm wheel shaft is required to adjust its position in the axial direction.In bevel gear transmission, the notional taper taper of two bevel gears must coincide, so it is required that both bevel gear shafts can be adjusted axially.