Timken2MMC9107WI DULHybrid Ceramic Super Precision Angular Contact Spindle Bearing Matched Pair, 35 x 62 x 14 mm each (28 mm set), 15 Degree, ABEC 7/9, Light Preload, Phenolic Cage

Product Description

What this part is

A factory matched pair of Timken Fafnir super precision angular contact ball bearings, 35 mm bore x 62 mm outside diameter x 14 mm wide each, supplied ground to a light preload for back-to-back or face-to-face duplex mounting. The rolling elements are silicon nitride ceramic balls in steel rings — a hybrid ceramic bearing, not a full ceramic one.

Decoding the designation 2MMC9107WI DUL

2MM – Fafnir super precision spindle bearing, 15° contact angle. The 25° equivalent would be 3MM.C (the extra letter in 2MMC) – hybrid ceramic ball complement. This is the whole reason the part exists and the reason it costs what it does.9107 – the 9100WI series, 35 mm bore. The ISO world part number for this bearing is C7007C-T-P4S-DUL: C for ceramic, 7007 for the envelope, C for 15°, T for the machined phenolic cage, P4S for the precision class, DUL for duplex universally ground with light preload.WI – Fafnir spindle bearing series designation.CR (as in the alternate designation 2MMC9107WICRDUL) – phenolic outer-land-riding cage. Same bearing; Timken’s own catalogue lists this part under the CR designation.DU – duplex, universally ground. Either bearing of the pair can go in either position, and they will mount back-to-back, face-to-face or in tandem without shims.L – light preload. M is medium, H is heavy.

What the ceramic balls actually do for you

Silicon nitride balls are roughly 40% the density of steel. Less mass means less centrifugal force at speed, which means less ball-to-outer-race contact stress, less heat, and less preload growth as the spindle warms up. That is why Timken publishes an operating speed uplift of about 120% of the steel-ball equivalent for the MMC ceramic spindle bearings, and why the limiting speeds here are 27,100 rpm on grease and 54,240 rpm on oil. Ceramic balls also do not gall against steel races the way steel does when lubrication is momentarily marginal, and they are electrically insulating — useful on motorised spindles and anywhere stray shaft current is a risk. What you give up is a slightly lower static rating and much less tolerance of shock loading: ceramic is harder and less forgiving than steel, so a dropped or hammered bearing is scrap.

Why 15 degrees and why light preload

The 15° contact angle is the high-speed choice. A shallower angle keeps ball spin and cage load down and lets the bearing run faster and cooler, at the cost of axial stiffness and thrust capacity compared with a 25° bearing. Combine that with light preload and you have a set specified for speed and thermal stability, not for heavy cutting thrust. If your spindle takes serious axial load — hard turning, heavy drilling — a 25° (3MM) medium-preload set is the correct part, not this one. Substituting a heavier preload into a position designed for light preload is one of the classic ways to cook a spindle.

Published ratings and mounting data (Timken)

Bore d: 35 mm. Outside diameter D: 62 mm (2.441 in). Width per bearing: 14 mm (0.551 in). Total width as a mounted set: 28 mm (1.102 in).Contact angle: 15°. Preload: light. Rows per set: duplex.Precision rating: ISO P4S, equivalent to ABEC 7/9.Dynamic radial load rating C1 (1 million revolutions): 21,200 N (4,760 lbf).C1 ISO dynamic radial rating per row: 19,300 N (4,340 lbf).Static radial load rating C0: 12,190 N (2,730 lbf).Limiting speed: 27,100 rpm grease, 54,240 rpm oil.Shaft backing shoulder diameter: 40.6 mm (1.600 in). Housing backing shoulder diameter: 56.6 mm (2.230 in).Maximum shaft fillet radius: 1 mm (0.039 in). Outer ring “to clear” radius: 1 mm (0.039 in).Cage: CR phenolic outer-land-riding, MBR cage material. Closure: open.

Quantity and configuration — verified from the goods

We photographed the actual item. The carton is marked 2MMC9107WI DUL with bore and OD grade marks (d-2, D-5) and lot number 2011747, and inside it there are two bearings still sealed together in the original factory wrap — an intact, unbroken matched pair. The bronze phenolic cage and the THRUST direction marking on the outer ring band are both visible in the photographs. This matters because DUL-marked cartons very often turn up with only one bearing left in them; this one has not been broken down.

One unit here = one complete matched pair = two bearings.

Fitting notes

Universally ground, so no shimming is needed and either bearing can take either position — but the THRUST marking on the outer ring must face the direction of the thrust load, and for a back-to-back set the two marked faces go outward. Do not separate the pair and mount the bearings in different positions in the machine; the preload was ground into them as a set. Handle with clean gloves, mount with a proper fitting tool or induction heater, and never press through the balls. Respect the backing shoulder diameters above — clamping onto the raceway land on a P4S bearing will destroy the running accuracy immediately. Grease fill should follow the spindle builder’s specification; over-greasing a 27,000 rpm bearing causes churning heat and preload runaway.

Interchange guidance

The ISO world part number is C7007C-T-P4S-DUL, and equivalents in the same envelope, angle, cage, class and preload include SKF 7007 CD/HCP4ADGA (HC = hybrid ceramic, CD = 15°, P4A, DGA = universally matched) and FAG/Schaeffler HCB7007-C-T-P4S-DUL. The steel-ball counterpart is 2MM9107WI DUL — dimensionally identical and considerably cheaper, but it will not reach these speeds and does not offer the electrical insulation. Do not cross to a plain 7007 industrial-class bearing; it shares only the boundary dimensions and none of the accuracy, cage or preload specification.