Deep groove ball bearing hole system, minus tolerance is why?

From the deep groove ball bearing is due to buy several bearing 6204 these days. Rolling bearing branch of the following is the centripetal bearing, centripetal bearings include deep groove ball bearings or centripetal ball bearings. Base hole of the bearing inner hole size is minus tolerance. The following two paragraphs or taken from 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. Add black is sound in a word, can think bearing base minus tolerance of hole system is to get more closely cooperate in conjunction with the same name, which cooperate with unapt too tight influence bearing function. That arrive at the clearance fit with the same name can reduce the interval or in transition fit, transition fit can reach the interference with the same name and and affect the bearing not much interference in operation. We seldom useful to figure 1 common rolling bearing the same name with the interference fit, ordinary once in the clearance or interference of the same name with a certain amount of interference. Same centripetal ball bearings of the tolerance zone is different from ordinary base hole system, the purpose is to fit for the fitting and and not too tight. Normal level 0 bearing normal not to mark on the bearing. Graph one about the bearing outer ring and the hole with same also USES the basic shaft system, the basic shaft system and ordinary, the bias of 0, but different from ordinary level 0 bearings tolerance zone of tolerance zone. As shown in figure 2, the level 0 6204 bearing outer ring size is 47, under his bias is 0. 009, related to the smaller figure 3 h7, so cooperate with clearance is small, also is the largest gap clearance fit quantity is small, which is with the same name will be tight. Figure 2 in figure three line '/>