In mechanical design, how are base hole system and base shaft system chosen?

Answer:

The shaft size is important, the base shaft system is chosen, and the hole size is important, so the base hole system is selected. For example, a shaft and shaft, the shaft is important, the size of high precision, choose the basic shaft system (also facilitate the processing of shaft sleeve hole). If the size of the inner bore of the shaft sleeve requires high accuracy, the base hole shall be used

Another example: there is a box on the outer circle of the bearing hole, you don't have to change when the hole of the bearing processing to realize the coordination, so only the basic shaft system (with cylindrical bearings as the base, change the pore size to realize the coordination)

Generally speaking, we should take the basic system as the first priority, but not the special case, so as to use the basic hole system. This is because it is more difficult to process the same size than the shaft.For example, the bearings of the bore and shaft coordination, as a result of general circumstances, you can not change the bearing bore to achieve coordination, so only the choice of base hole system. (with the bore as the base, change the size of the shaft to achieve alignment)

This should be divided into several cases to deal with, we must first understand what is called the base hole system, what is called the basic axis system?. The so-called base hole system is the size of the hole must change the size of the shaft to meet the needs of the coordination. Similarly, the so-called base axis system is the size of the shaft must change the size of the hole to meet the needs of the match.