RHP7008ETDUMP4Super-Precision Angular Contact Ball Bearing Duplex Pair – 40 mm Bore, 68 mm OD, 15 mm Width, 25 Degree Contact Angle, Medium Preload, Phenolic Cage, ABEC 7, Open

Product Description

What this part is

An RHP super-precision angular contact ball bearing, 40 mm bore, 68 mm outside diameter, 15 mm width per bearing, supplied as a duplex pair with medium preload. RHP is the British line of NSK and shares its super-precision nomenclature. The 7008 designation places it in the ISO 70 light series at the 08 bore code, so the boundary dimensions follow the ISO standard.

Decoding the designation

This bearing carries two factory designations and they cross-confirm each other. In 7008-E-T-DUM-P4 the E denotes a 25° contact angle in the RHP scheme, T a fabric-base laminate phenolic cage, DU a duplex pair, M medium preload, and P4 the precision class. In the alternative B-series designation B7008X3TADUMEP7 the X3 independently denotes 25°, and EP7 is the same precision class as P4. Two separate designations agreeing on both angle and class is the useful property of RHP cartons.

What these specs mean in practice

A 25° contact angle sits between the 15° high-speed setting and the 40° high-thrust setting. It carries appreciably more axial load than a 15° bearing of the same envelope and runs at a lower ceiling speed, which is the usual compromise for a spindle that must take cutting thrust as well as turn quickly. Medium preload gives more stiffness than light preload at the cost of higher running torque and more heat, so it suits shorter or more heavily loaded duty cycles. A phenolic cage is light and self-lubricating, tolerates marginal lubrication better than steel, and is the standard choice for high-speed super-precision bearings; its ceiling is temperature rather than load.

Load ratings and speed

Dynamic load rating 17.5 kN (3,935 lbf), static load rating 11.5 kN (2,585 lbf), limiting speed 24,000 rpm on oil. Operating range −30 °C to 120 °C.

Thrust direction and arrangement

A single-row angular contact ball bearing takes thrust in one direction only. Assembled as a duplex pair the arrangement carries thrust in both directions and the ground ring-face offset sets the medium preload. Universal grinding means any two bearings of this designation may be arranged back-to-back, face-to-face or in tandem and will develop the specified preload when clamped.

Quantity and configuration

2 Pcs, one duplex pair. The 15 mm width is per bearing, giving 30 mm across the assembled pair. Open on both faces, no snap ring groove.

Fitting notes

Preload develops as the ground faces are clamped together, so shaft and housing shoulders act as the datum and clamp load must reach the ring faces squarely. Phenolic cages set a temperature ceiling on the assembly, which makes the lubrication regime and the resulting running temperature the governing constraint at high speed.

Interchange guidance

Fafnir 3MM9108WI-CR-DUM is a genuine interchange: the 3MM prefix denotes 25°, the CR a phenolic outer-land-riding cage and DUM a medium-preload duplex pair, matching this bearing on all four counts. Same-envelope 7008 bearings at 15° (C or X2) or 40° are related sizes rather than interchanges, as are light or heavy preload variants of the same number.