Talk about with the shaft, bearing assembly - Base hole system is not rigorous

Transmission system, driving system, that is to say, turn the local cannot leave the bearings, also cannot leave the hole and shaft. Learning mechanical people all know that the bearing and shaft are ordinary base hole system, because the bearing is standard parts, shaft is designed according to the practice situation to stop. On base hole system, we understand the base hole system seems to be the hole under bias is 0, the bias is a certain value, the tolerance zone, code-named H, a certain tolerance level. But if not so for rolling bearing. For example, 6204 of centripetal ball bearings, he is the inner diameter of 20 mm, about the base hole system, he should be under bias is 0, the practice condition, is not the case, the centripetal ball bearings on bias is 0, the bias is negative. I looked at the mechanical design manual: to avoid 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 avoid shaft and the inner ring relative sliding of the most simple and effective way. Especially the thin ring of bearing, adopting appropriate tight fit can make the stress when the bearing ring is moving average, so that the bearing of the bearing to get its full play. But with the bearing and can't be too tight, because elastic contraction of inner ring and outer ring shrinkage reduce bearing radial clearance so that a complete alleviation, thus affect the normal operation. Bearing and shaft diameter d, base hole system, but the tolerance zone located below the zero line, the bias of 0, compared with common base hole system, in conjunction with the same name are more likely to get more closely cooperation. Cooperate with shell hole diameter D shaft basis, its tolerance zone is the same as ordinary shaft basis, located below the zero line, the bias of 0, but compared with the general tolerance system, the tolerance zone is incomplete. Cooperate with hole and shaft bearing compared to common is loose. The above two paragraphs from mechanical design manual said in the first paragraph needs tight fit, but not too tight. Here is a tight one. The second paragraph is the base hole system, but also different from ordinary base hole system. Same name with I add black, meaning is: in common base hole system clearance fit, the bearing fit to transition fit, in ordinary base hole system transition fit, the bearing fit interference fit can arrive, or it is the largest gap become smaller, the greater than surplus.