Fafnir3MM9114WIDULSuper Precision Angular Contact Ball Bearing, Duplex Pair, 70 x 110 x 20 mm, 25° Contact Angle, Light Preload, Phenolic Outer-Land-Riding Cage, ABEC 7/9

Product Description

What this part is

A super precision angular contact ball bearing for machine tool spindles, supplied as a universally ground duplex pair at light preload. Each bearing is 70 mm bore by 110 mm outside diameter by 20 mm wide; assembled the pair is 40 mm wide. This is a spindle bearing, not a general-purpose or automotive ball bearing: the tolerance grade, the phenolic cage and the ground faces exist to hold a shaft concentric at high rpm under a combined radial and axial load.

Decoding the designation

3MM — Fafnir/Timken super precision metric series with a 25° contact angle.
9114 — 9100WI dimension series, 70 mm bore.
WI — the standard Fafnir super precision spindle angular contact ball bearing series.
CR — phenolic outer-land-riding cage (Timken cage designation MBR).
DU — duplex universally ground, a matched pair that mounts in any orientation without shims.
L — light preload.
MM prefix — implies ISO P4S (ABEC 7/9), not P4.

Correcting the source data

The original listing carried a model string reading “3MM 9114 WI CR DUL / 7014 E T SUL P4 / 7014A / 7015A5”, and most of it was wrong. Timken’s own published world part number for this bearing is 7014E-T-P4S-DUL. Four corrections follow from that.

P4 should be P4S. The MM prefix carries the P4S grade, so a world number written with P4 is the error.
SUL should be DUL. The old string contained both, and they are mutually exclusive — SU is a single bearing, DU is a matched pair. The part number itself, the carton form and Timken’s catalogue all say DUL, so the stray SUL is a transcription error and the item is a duplex pair.
7014A is not Timken’s designation. The letter after the series number is the contact angle, and 3MM means 25°, which is E. Timken publishes 7014E. The 7014A form is retained as a search term only, not as an equivalent.
7015A5 has been deleted outright. It refers to the 7015 series, a 75 x 115 x 20 mm bearing — a different bore, a different outside diameter and a different part. Leaving it in place would invite a wrong-part substitution, so it has been removed rather than demoted.

The “Manufactured in: United States” claim has also been removed. Nothing in Timken’s published data or in the carton markings establishes an origin, and Fafnir cartons have read England.

What these specs mean in practice

The 25° contact angle is the rigidity-biased choice. Against a 15° bearing in the same envelope, the steeper angle carries substantially more thrust and deflects less axially under load, which is what a spindle taking real cutting thrust needs. What it costs is speed: a steeper angle raises ball spin, gyroscopic moment and cage loading, so the limiting speed and the heat generated at a given rpm are both worse than the 15° part. Choose 25° for stiffness, 15° for rpm.

Light preload pulls the other way, and the combination is deliberate. Pairing a stiff 25° contact angle with the lightest preload class gives you the thrust capacity and axial rigidity of the steep angle while keeping friction, heat generation and grease consumption to a minimum — a sensible compromise for a spindle that must be both reasonably stiff and reasonably fast. Preload class is not a free substitution: fitting a DUM or DUH set where the machine was designed around DUL will change both the stiffness and the thermal behaviour of the spindle.

The phenolic outer-land-riding cage is what keeps a 25° bearing viable at speed. Phenolic is light and mildly self-lubricating, so it generates far less heat than a steel cage, and riding on the outer ring land lets centrifugal force stabilise the cage rather than load it. Two practical rules follow: never clean these in solvents that attack phenolic, and never run them dry.

Published ratings and mounting data

Contact angle: 25°
Precision: ISO P4S (ABEC 7/9)
Preload: light
Rows per set: duplex (two)
Bore 70 mm, outside diameter 110 mm, width 20 mm per bearing, total assembled width 40 mm
Dynamic radial load rating C1, 1 million revolutions: 10,700 lbf / 47,600 N
C1 ISO dynamic radial rating per row: 9,730 lbf / 43,300 N
Static radial load rating C0: 8,730 lbf / 38,800 N
Limiting speed, grease: 11,600 rpm
Limiting speed, oil: 21,000 rpm
Maximum shaft fillet radius: 1 mm
Shaft backing shoulder diameter: 77.7 mm
Housing backing shoulder diameter: 102.4 mm
Outer ring “to clear” radius: 1 mm

These are Timken’s own published catalogue figures for 3MM9114WI DUL. They belong to the 25° 3MM variant; the 15° 2MM9114WI carries different ratings and the two must not be interchanged on paper.

Quantity and configuration

DUL designates a duplex pair, so the sale unit is two bearings ground and matched to each other as a set. They are supplied and priced as one set and cannot be split without losing the matched preload. Because matched pairs do get separated in surplus handling, confirm both bearings are present before fitting if the application depends on it.

Fitting notes

Universally ground rings let the pair be mounted back-to-back, face-to-face or in tandem, but they must be assembled in the orientation the machine calls for and clamped square. Preload is developed by clamping the ground faces solidly together, so a burr, a dirt film or an out-of-square abutment on the shaft or housing shoulder translates directly into wrong preload and lost running accuracy — and on a light-preload set there is very little margin before the preload is lost altogether. Respect the 77.7 mm shaft and 102.4 mm housing backing shoulder diameters and leave the 1 mm fillet clearance. Handle by the outer ring, keep the pair in its packaging until the moment of assembly, and run the spindle in progressively before applying full speed.

Interchange guidance

Timken’s published world equivalent is 7014E-T-P4S-DUL, where E denotes the 25° contact angle, T the phenolic cage and P4S the precision grade. A valid substitute must match on contact angle, precision grade, preload class, cage material and the duplex arrangement together — matching only the 70 x 110 x 20 mm envelope is not enough, and a 15°, steel-caged or clearance-graded 7014 is a different bearing in the same box size. Fafnir super precision bearings are now supplied under the Timken brand, so Fafnir and Timken designations of this form are the same product line.