Timken2MM9109WITUMSuper Precision Angular Contact Ball Bearing, Triplex Matched Set of 3, 45 x 75 x 16 mm, 15 Degree Contact Angle, Medium Preload, Phenolic Outer-Land-Riding Cage, ABEC 7/9

Product Description

What this part is

Timken Fafnir 2MM9109WI-TUM, a super precision angular contact ball bearing for machine tool spindles, supplied as a universally ground triplex set of three matched bearings. Brand: Timken (Fafnir). Bore: 45 mm. Outside Diameter: 75 mm. Overall Width: 16 mm per bearing. Total Width: 48 mm as an assembled triplex set. Contact Angle: 15°. Preload: Medium. Precision Class: ISO P4S, ABEC 7/9. Arrangement: TU, triplex universally ground. Number Of Rows: three, one row per bearing. Cage Material: Phenolic, Timken cage designation MBR. Cage Type: CR, outer-land-riding. Rolling Elements: Steel balls. Bearing Material: Chrome steel rings and balls with a phenolic cage. Closure Type: Open. Series: 9100WI, 2MM super precision metric. Base Number: 2MM9109WI. Design Units: Metric. This is a machine tool spindle bearing: its tolerance grade, phenolic cage and 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: 6,080 lbf, 27,000 N. C1 ISO Dynamic Radial Rating per row: 5,530 lbf, 24,500 N. Static Radial Load Rating C0: 4,330 lbf, 19,300 N. Limiting Speed: 17,900 rpm on grease, 35,800 rpm on oil. Maximum Shaft Fillet Radius: 1 mm. Shaft Backing Shoulder Diameter: 51.3 mm. Housing Backing Shoulder Diameter: 69.3 mm. Outer Ring To-Clear Radius: 1 mm. These are Timken’s published catalogue figures for 2MM9109WI TUM and belong to the 15° 2MM variant; a 25° 3MM9109WI carries different ratings.

Decoding the designation

2MM: Fafnir and Timken super precision metric series, 15° contact angle. 9109: 9100WI dimension series, 45 mm bore. WI: the standard Fafnir super precision spindle angular contact ball bearing series. CR: phenolic outer-land-riding cage, Timken designation MBR. TU: triplex universally ground, three bearings ground as one matched set; the family runs SU single, DU duplex pair, TU triplex, QU quadruplex. M: medium preload. The MM prefix carries ISO P4S, ABEC 7/9.

The letter T does two jobs in this family. In the arrangement suffix TUM the T means triplex. In Timken’s world part number 7009C-T-P4S-TUM the standalone T between the series and the precision grade means the phenolic cage. Searchable variants: 2MM9109WI-TUM, 2MM9109WITUM, 2MM-9109-WI-CR-TUM, 2MM9109WICRTUM, 2MM 9109 WI TUM, 2MM9109WI, 7009C-T-P4S-TUM, 7009C.

What these specs mean in practice

A triplex set solves a problem a pair cannot. Three bearings are normally arranged two in tandem against one, so the two sharing the same direction roughly double the thrust capacity and axial stiffness on that side while the third handles thrust the other way and keeps the set located. That suits a spindle with a strongly one-directional cutting thrust, or a vertical spindle carrying its own weight. The cost is width, heat and complexity: three rows generate more friction than two, and the whole stack clamps as a unit.

The 15° contact angle keeps the set fast. A shallower angle holds the ball load line closer to radial, reducing ball spin, gyroscopic moment and cage load, so the bearing runs cooler and higher than a 25° equivalent. It trades away axial stiffness per row, which is why a triplex arrangement is a sensible way to recover thrust capacity without a steeper, slower angle.

Medium preload is the middle of the three classes. It gives more axial stiffness and better load sharing between rows than light preload, with less friction, heat and grease consumption than heavy. On a three-row set that balance matters more than usual, because friction losses are already multiplied by the extra row. Preload class is part of the spindle design: a TUL or TUH set changes both the stiffness the machine relies on and its thermal behaviour.

The phenolic outer-land-riding cage is the high-speed enabler. Phenolic is light and mildly self-lubricating, so it generates far less heat than steel, and riding on the outer ring land lets centrifugal force stabilise the cage rather than load it. Phenolic is attacked by some solvents.

Quantity and configuration

Unit Quantity: 1 matched triplex set, three bearings. The three are ground and matched to each other and are supplied and priced together; the ground preload relationship exists across the set as a whole.

Fitting notes

Universally ground faces allow assembly in the arrangement the machine calls for without shims. The ground faces go together in the sequence and direction the spindle design specifies, and the three-row stack clamps solidly and square. Preload develops from that clamping, so a burr, a dirt film or an out-of-square shoulder on the shaft or housing translates directly into wrong preload across all three rows and lost running accuracy. The 51.3 mm shaft and 69.3 mm housing backing shoulder diameters apply, with 1 mm fillet clearance. Handling is by the outer ring, in the original packaging until assembly, with the stack order marked before separation and a progressive run-in before full speed.

Interchange guidance

Timken’s published world equivalent is 7009C-T-P4S-TUM, where C denotes the 15° contact angle, T the phenolic cage and P4S the precision grade. The MM prefix carries P4S. A matching substitute carries a 15° contact angle, ISO P4S, a phenolic cage, medium preload and the triplex arrangement together. A duplex pair, a 25° 3MM9109WI or 7009E, and a steel-caged 7009 in the same 45 x 75 x 16 mm envelope are related sizes. 2MMV99109WN shares the envelope with a different cage and design execution, its own published ratings and a much higher speed limit. Fafnir super precision bearings are supplied under the Timken brand, so Fafnir and Timken designations of this form are the same product line.