Fafnir2MM9118WI-DULSuper-Precision Angular Contact Spindle Bearing, Matched Pair, 90 x 140 x 24 mm, 15 Degree, ABEC-7, Light Preload

Product Description

What this part is

This is a MATCHED PAIR of super-precision angular contact ball bearings – two bearings, 90 mm bore x 140 mm outside diameter x 24 mm wide each, the 7018 envelope. Both are present and still in the sealed factory bag.

The designation decodes element by element against Timken’s Fafnir lettering system. The leading 2 is the contact angle: 2 means 15 degrees, 3 means 25 degrees. MM is the precision level, superprecision to ABEC-7. 9118 is the 9100 extra-light series with bore code 18, which is 18 x 5 = 90 mm. WI means angular contact with the low shoulder counterbored into the OUTER ring. DUL is the important one: Duplex, Universal, Light preload.

What the 15 degree angle trades away

A shallow contact angle puts more of the ball load into the radial direction and less into thrust, so a 15 degree bearing carries less axial load than a 25 degree one – but it runs faster, generates less heat and gives higher radial stiffness. That is exactly the compromise a machine-tool spindle wants: high speed, tight radial runout, modest thrust. If your spindle is thrust-dominated, such as a heavy drilling or boring head, the 25 degree 3MM9118WI is the correct part and this one is not.

What DUL means for how you fit it

Universally ground means the faces of both bearings are flush-ground to a controlled offset, so the same pair can be stacked back-to-back (DB) for maximum moment stiffness, face-to-face (DF) for tolerance of slight misalignment, or in tandem (DT) to double thrust capacity in one direction. You choose the arrangement at assembly; the bearings do not care. Light preload sets the residual load that removes internal clearance without cooking the bearing at speed – light is the high-speed, low-heat end of the range.

The outer ring is marked THRUST with a direction arrow. On a preload-matched pair that marking is not decoration: it tells you which way round each ring goes so the preload lands where the designer intended. Mount them against the marking and keep the pair together – once separated and mixed with bearings from another set, the matched grinding is worthless and the preload is gone.

Handling

these are open bearings, no seals or shields, because a super-precision spindle bearing is lubricated by the spindle system, not by grease trapped behind a seal. Keep them bagged, clean and dry until the moment of assembly, and mount with proper tooling – a hammer on an ABEC-7 ring destroys it.

Cross-references for the same envelope and duty

7018 is the ISO base number, and the equivalent world designation for a 15 degree, ABEC-7, universally ground light-preload duplex pair is written 7018C-T-P4S-DUL. Fafnir is now part of Timken, so current-catalogue equivalents carry Timken numbering. Also written 2MM-9118-WI-DUL, 2MM9118WIDUL and 2MM9118WI DUL.