The Design of Rolling Bearing Mountings

10 NC-lathe main spindleOperating dataInput power 27 kW;maximum spindle speed 9,000 min –1 .Main spindle bearings do not normally fail due to materialfatigue but as a result of wear; the grease servicelife is decisive.Bearing selectionThe main requirements on this bearing arrangementare an extremely good speed suitability, rigidity, andaccurate guidance of the work spindle. At the workend, a spindle bearing set FAG B7017C.T.P4S.DTLin tandem arrangement is provided; at the drive end, aspindle bearing set FAG B71917C.T.P4S.DTL intandem arrangement.The bearings are lightly preloaded (UL) and have anincreased precision (P4S).The arrangement has no floating bearing; it is a rigidlocating bearing system. Both bearing groups togetherform an O arrangement.Bearing clearanceFAG spindle bearings of universal design are intendedfor mounting in X, O or tandem arrangement in anyarrangement. When mounting in X or O arrangement adefined preload results. The light preload UL meetsthe normal requirements.The original preload remains in the bearings due toouter and inner spacer sleeves of identical lengths.With a good bearing distance, the axial and radial heatexpansions of the work spindle compensate each otherso that the bearing preload remains unchanged underany operating condition.Bearing dimensioningThe size of the bearings is primarily based on the spindlerigidity required, i. e. on the largest possible spindlediameter. The fatigue life of the bearings is takeninto account for dimensioning but it does not play adominating role in practice.Lubrication, sealingThe bearings are greased for life with the FAG rollingbearing grease Arcanol L74V and about 35 % of thecavity is filled.Sealing is provided by labyrinth seals with defined gaps.Machining tolerancesBearing Seat Diameter Form tolerance Axial run-out tolerance oftolerance (DIN ISO 1101) abutment shoulderSpindle bearings Shaft +5/–5 µm 1.5 µm 2.5 µmDrive end/work end Housing +2/+10 µm 3.5 µm 5 µm10: NC-lathe main spindleFAG 22