Fafnir2MM9115WIDULSuper Precision Angular Contact Ball Bearing, 75 x 115 x 20 mm, 15 Degree Contact Angle, Light Preload, Phenolic Outer-Land-Riding Cage, Universally Ground, ABEC 7/9

Product Description

What this part is

Fafnir 2MM9115WI, a Timken super precision angular contact ball bearing for machine tool spindles. Brand: Fafnir (Timken). Bore: 75 mm. Outside Diameter: 115 mm. Overall Width: 20 mm per bearing. Contact Angle: 15°. Preload: Light. Precision Class: ISO P4S, ABEC 7/9. Cage Material: Phenolic, Timken cage designation MBR. Cage Type: CR, outer-land-riding. Mounting Arrangement: Universally ground. Number Of Rows: 1 row per bearing. Rolling Elements: Steel balls. Bearing Material: Chrome steel. Closure Type: Open. Bore Type: Straight. Series: 9100WI, 2MM super precision metric. Base Number: 2MM9115WI. Design Units: Metric. Harmonization Code: 8482.10.50.28. This is a spindle bearing: the tolerance grade, the cage and the universally ground faces exist to hold a shaft concentric at high rpm under a combined radial and axial load.

Published ratings and mounting data

Dynamic Radial Load Rating C1 at 1 million revolutions: 11,600 lbf, 51,600 N. C1 ISO Dynamic Radial Rating per row: 10,500 lbf, 46,800 N. Static Radial Load Rating C0: 9,790 lbf, 43,500 N. Limiting Speed: 11,000 rpm on grease, 22,000 rpm on oil. Maximum Shaft Fillet Radius: 1 mm. Shaft Backing Shoulder Diameter: 82.7 mm. Housing Backing Shoulder Diameter: 107.3 mm. Outer Ring To-Clear Radius: 1 mm. Operating Temperature Range: -20 °C to 120 °C. These are Timken’s published catalogue figures for 2MM9115WI and are the same for the CRSUL and CRDUL executions. They belong to the 15° 2MM variant; a 25° 3MM9115WI carries different numbers.

Decoding the designation

2MM: Fafnir and Timken super precision metric series, 15° contact angle. 9115: 9100WI dimension series, 75 mm bore. WI: the standard Fafnir super precision spindle angular contact ball bearing series. CR: phenolic outer-land-riding cage, Timken designation MBR. SU: single universally ground. DU: duplex universally ground, a matched pair. L: light preload. The MM prefix carries ISO P4S, ABEC 7/9. Searchable variants: 2MM9115WI, 2MM9115WI-SUL, 2MM9115WICRSUL, 2MM-9115-WI-CR-SUL, 2MM9115WI-DUL, 2MM9115WICRDUL, 2MM-9115-WI-CR-DUL, 2MM 9115 WI CR DUL.

What these specs mean in practice

The 15° contact angle is the speed-biased choice. A shallower angle runs the ball load line closer to radial, which reduces ball spin, gyroscopic moment and cage load, so the bearing runs cooler and faster than the 25° equivalent. It trades away axial stiffness and thrust capacity: for a given preload a 15° set deflects more under thrust than a 25° set. 15° buys rpm and thermal headroom; 25° buys rigidity under heavy cutting thrust.

Light preload continues in the same direction. It gives the lowest friction, the least heat and the longest grease life of the three preload classes, at the cost of axial stiffness and load-sharing rigidity. It is the normal choice for high-speed grinding and finishing spindles. Preload class is part of the spindle design: a spindle designed around DUL runs hotter and loses life with a DUM or DUH set, and one designed for DUH loses its designed stiffness with a DUL set.

The phenolic outer-land-riding cage is the enabling detail for that speed. Phenolic is light and mildly self-lubricating, so it generates much less heat than steel, and riding on the outer ring land lets centrifugal force stabilise the cage instead of loading it. Phenolic is attacked by some solvents and degrades in prolonged heat.

Fitting notes

Universally ground faces allow mounting in any orientation and pairing with another universally ground bearing of the same designation without shims. Preload develops by clamping those ground faces solidly and squarely, so a burr, a dirt film or an out-of-square shoulder translates directly into wrong preload and lost accuracy. The 82.7 mm shaft and 107.3 mm housing backing shoulder diameters apply, with 1 mm fillet clearance. Handling is by the outer ring, in the original packaging until assembly, with a progressive run-in before full speed and full lubricant flow.

Interchange guidance

Timken’s published world part numbers are 7015C-T-P4S-SUL for the single and 7015C-T-P4S-DUL for the pair, where C denotes the 15° contact angle, T the phenolic cage and P4S the precision grade. The MM prefix carries P4S. A substitute matches on contact angle, precision grade, preload class and cage material together, alongside the 75 x 115 x 20 mm envelope. A 25° 3MM9115WI or 7015E in the same envelope is a related size. Fafnir super precision bearings are supplied under the Timken brand, so Fafnir and Timken designations of this form are the same product line.