Talk about with the shaft, bearing assembly - Loosely - bearing knowledge base hole system

Transmission system, driving system, that is to say, cannot leave the bearing rotating part, also cannot leave the hole and shaft. Learning mechanical knows that bearings and shaft are generally base hole system, because the bearing is standard parts, is according to the actual situation to carry on the design of the shaft. About base hole system, we understand the base hole system as hole deviation is 0, the deviation is a certain value, tolerance zone, code-named H, a certain tolerance level. But it may not seem like it for rolling bearing. For example, 6204 of centripetal ball bearings, he is the inner diameter of 20 mm, for the base hole system, he should be lower deviation is 0, the actual situation is not so, centripetal ball bearings on deviation is 0, the deviation is negative. I looked at the mechanical design manual: in order to prevent the bearing inner ring and shaft, outer ring and shell holes produce should not have the relative sliding when the machine is running, must choose the right fit. Usually axis and the inner ring with proper fit is to prevent shaft and the inner ring relative sliding of the most simple and effective method. Especially for thin wall ring bearing, using appropriate tight fit can make the bearing ring in sports uniform stress, and give full play to the bearing capacity. But with the bearing and can't be too tight, due to the elastic expansion of inner ring and outer ring contraction makes bearing radial clearance, reduce or even eliminate thus affect the normal operation. Bearing and shaft diameter d, base hole system, but the tolerance zone located below the zero line, the upper deviation is 0, compared with the general base hole system, in conjunction with the same name are more likely to get more close cooperation. Diameter D cooperate with shell hole of shaft basis, its tolerance zone is the same as general shaft basis, located below the zero line, the deviation is 0, but compared with the general tolerance system, its tolerance zone are not identical. Bearings with holes compared with shaft are loose. The above two paragraphs from mechanical design manual in the first paragraph said in need of a tight fit, but not too tight. There is a degree that there is a tight. The second paragraph is the base hole system, but different from that of general base hole system. Same with added black, I mean is: in general base hole system clearance fit, the bearing fit to transition fit, in general base hole system transition fit, the bearing fit can reach interference fit, or it is the largest gap become smaller, the greater than surplus.