The Design of Rolling Bearing Mountings

11 CNC-lathe main spindleOperating dataInput power 25 kW;Speed range 31.5...5,000 min –1 .Apart from the Hertzian contact pressure, the servicelife of the bearings is mainly dictated by the greaseservice life. Main spindle bearings do not normally faildue to material fatigue but as a result of wear.Bearing selectionThe bearings must accurately guide the spindle radiallyand axially and be very rigid. This is achieved by selectingas large a shaft diameter as possible and a suitablebearing arrangement. The bearings are preloaded andhave an increased precision.At the work end a spindle bearing set FAGB7018E.T.P4S.TBTL in tandem-O-arrangement witha light preload is mounted as locating bearing.At the drive end there is a single-row cylindrical rollerbearing FAG N1016K.M1.SP as floating bearing.This bearing arrangement is suitable for high speedsand for high cutting capacities.Bearing dimensioningThe bearing size is primarily based on the spindlerigidity required, i.e. on the spindle diameter. Thefatigue life of the bearings is taken into account fordimensioning but it does not play a dominating role inpractice.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 aset preload results. The light preload UL meets thenormal requirements.The cylindrical roller bearing is adjusted with almostzero radial clearance by axially pressing the taperedinner ring onto the spindle.Lubrication, sealingThe bearings are greased for life with the FAG rollingbearing grease Arcanol L74V.Approximately 35% of the spindle bearing cavity andapproximately 20% of the cylindrical -roller bearingcavity is filled with grease.Sealing is provided by a labyrinth with set narrowradial gaps.Machining tolerancesBearing Seat Diameter Form tolerance Axial runout tolerancetolerance (DIN ISO 1101) of abutment shoulderSpindle bearings Shaft +5/–5 µm 1.5 µm 2.,5 µmHousing –4/+8 µm 3.5 µm 5 µmCylindrical roller bearings Shaft, tapered Taper 1:12 1.5 µm 2.5 µmHousing –15/+3 µm 3.5 µm 5 µm11: CNC-lathe main spindle23 FAG