Fafnir2MM9517WIDUMSuper-Precision Angular Contact Ball Bearing Duplex Set of 2 – 85 mm Straight Bore, 130 mm OD, 24 mm Width Each, 15° Contact Angle, Open, Phenolic Outer-Land-Riding Cage, Medium Preload

Product Description

What this part is

Fafnir 2MM9517WI-DUM super-precision angular contact ball bearings, 85 mm bore, 130 mm outside diameter, 24 mm width per bearing. Single row each, open on both faces, machined phenolic outer-land-riding cage. Fafnir 9500 WI series. Two pieces, supplied as a duplex set.

Decoding the designation

2MM sets a 15° contact angle in the Fafnir WI super-precision scheme, and the MM prefix carries P4S precision — ABEC 7 dimensional tolerances with ABEC 9 running accuracy. WI is the ground spindle-bearing execution, CR the phenolic outer-land-riding cage, and DUM a duplex arrangement at medium preload.

What these specs mean in practice

Basic dynamic capacity is 72 kN (16,186 lbf) and static capacity 65 kN (14,612 lbf), with a limiting speed of 9,000 rpm. The 15° angle favours speed and radial stiffness; a 25° bearing of the same envelope would take more thrust and turn slower. The phenolic cage rides on the outer-ring land, which stabilises it at speed and tolerates oil-mist lubrication. Medium preload is the middle setting, chosen where a spindle needs stiffness under cutting load without the thermal penalty of a heavy setting.

Quantity and configuration

Two bearings, 24 mm wide each, 48 mm total mounted width as a duplex stack. Universally ground faces, so the pair mounts back-to-back, face-to-face or in tandem.

Fitting notes

Straight bore on an interference fit to the spindle journal, outer rings clamped square in the housing bore. The ground faces are stacked with the marked faces oriented together per the chosen arrangement, and the medium preload is developed by the ground offsets. Operating range is –30 to 120 °C on oil or grease.

Interchange guidance

The 9500 WI series at this size runs 24 mm wide. The ISO 7017 bearings from other super-precision makers — FAG B7017-C-T-P4S-DUM, SKF 7017 CD/P4ADGB, NSK 7017CTYDUMP4, RHP 7017ETDUMP4 and GMN S6017 C TA P4 — share the 85 mm bore, the 130 mm outside diameter, the 15° angle and the medium preload, but measure 22 mm wide. The 2 mm difference in width per bearing changes the stack height of a duplex pair by 4 mm.