THE INITIAL CLEARANCE AND OPERATIONAL CLEARANCE
           The normal operation of rolling bearings mainly depends on its suitable operational clearance which is
       decided by initial radical clearance of the selected tolerance combination and temperature before assembling.

             The initial radical clearance of the rolling bearings is the position variation between the two top
        positions of the inner rings related to the outer ring in radical direction without radical force before 
        assembling.
             Normal initial radical clearance C0 of RTL needle bearings and cylindrical roller bearings are sel-
        ected as per the technical remarks before the dimension table or the recommended shaft and bearing seats 
        tolerances and the operational clearance under normal operational condition which will ensure to reach the
        normal functions.
             Under other assembling conditions and operational conditions, for instance, the interference combi-
        nation of the bearing bush rings, special bearing temperature etc,in such cases the required bearing ini-
        tial radical clearances are different from those normal ones. The  centripetal bearings with the initial 
        radical clearance different from the normal ones can be marked with supplemental codes listed in table 28.
             These supplemental codes (except C0) are added after the bearing codes or combined with the supplem-
        ental codes of the precision grades.
             Table 29 shows the clearance value of different groups of bearings. For the needle bearings without 
        inner rings supplied by RTL, the tolerance range of its inscribed cycle is F6.
             The initial radical clearance of C2 is only used for extremely special cases ,  for instance heavy 
       alternative loads and low speed  operation or the swinging movement. In these cases, greater heat will be 
       produced . So it is suggested that the bearing should be monitored during its operation.
             The initial radical clearances of C3 and C4 are used for the case of bush ring for interference co-
       mbination or greater temperature gradients between inner and outer rings, especially for the case of big
       bearings.

           Table 28  initial radical clearance codes

           Table 29  initial radical clearances of the needle bearings and cylindrical roller bearings

              The operational clearance of the bearings is defined as: the radical deviation of the shaft from the
         bearing outer ring under no load condition. Operational clearance is initial radical clearance subscribed 
         by the clearance variation caused by interference combination and heat expansion expressed with ΔS (μm  
         as its unit)

ΔS=ΔSP+ΔST    .............................(44)

               As the reduction quantity of the clearanceΔSp caused by interference combination can be got through
         equation (46) and the reductionΔST caused by heat expansion can be calculated through expression (46). The
         symbols of positive negative should be noticed during calculation.
               
               lNORMAL OPERATIONAL CLEARANCE
               Under normal operational conditions , if the bearing with inner ring are combinative with the bearings
         seats and shaft within the selected tolerance range in table 14 and table 15, the bearings with initial ra--
         dical clearance C0 usually can get normal operational clearance.
               lOPERATIONAL CLEARANCE SMALLER THAN NORMAL OPERATINAL CLEARANCE
               For rolling bearings, the smaller clearance can be only used in special cases, for instance, precision
         machine tools, measuring instruments or the cases with alternative loading.
               lOPERATIONAL CLEARANCE BIGGER THAN OPERATIONAL CLEARANCE
               Bigger clearance bearings are mainly used in the cases where relative slope and shaft bending exist.
　　　　　　　THE EFFECT OF COMBINATION ON THE OPERATIONAL CLEARANCE
　　　　　　　　The initial radical clearance reductionΔSp (μm) is the result of the expansion quantity of inner 
　　　　ringΔd and the subtraction of outer ring ΔD.

ΔSP=Δd +ΔD ...............................(45)

　　　　　　　　Practice shows that there are two ways to decide the interference quantity of the combinative parts: 
　　　　one is to take the mean deviation while the other is to take the deviation limit value close to the machining 
　　　　face then plus or minus 1/3 of the tolerance range value　.　 Again the mutual compressive value between the
　　　 surfaces in assembling must be subtracted. The mean value of the dimension variation are listed in table 30.
　　　　　　　　For the thin wall bearing seats and light metal bearing seats, the effective interference quantity 
　　　　can not be got reliably through calculation. In this case it is suggested to decide the reduction quantity 
　　　　of the initial radical clearance  through assembling tests.
                THE TEMPERATURE EFFECTS ON THE OPERATIONAL CLEARANCE
                Where there are bigger temperature gradient between inner and outer rings of the bearing, the vari-
        ation of the bearing operation clearance  will become rather big thus causing abnormal effect of the bearing
        normal functions. For example, take the steel heat expansion factor as α=0.000011 (K-1 ) , the temperature 

 ΔST≈0.11.dM.Δv    .........................(46)

               The temperature variation Δvbetween inner and outer rings can cause operational clearance  to decrease
        or increase. Therefore positive or negative symbols must be noticed when Δ    in Formula (46) is used. If the
        inner rig temp is higher than the outer ring, Δ    should be positive while negativeΔ    should be used vise 
        versa

　　　　　　　Table 30 the diameter variation caused by interference combination