FAGB7028CAP4ULSuper Precision Angular Contact Ball Bearing 140 x 210 x 33 mm, 15° Contact Angle, P4S Tolerance, Phenolic Cage, Universal Light Preload

Product Description

What this part is

A super precision angular contact ball bearing in the 7028 envelope — 140 mm bore, 210 mm outside diameter, 33 mm width. This is FAG’s spindle bearing range: single row, open, universally ground, and made to the tolerance grade that machine tool builders specify for main spindle positions.

Decoding the designation

B — FAG spindle bearing series, a higher-precision execution than a standard 70-series angular contact bearing.
7028 — ISO boundary dimensions, 140 x 210 x 33 mm.
C — 15° contact angle in FAG nomenclature. This is the single most important character in the number and the one most often misread.
T — phenolic (textile laminate) cage.
P4S — super precision tolerance, ABEC 7 running accuracy with tighter bore and outside diameter control, plus matched width for universal grinding.
UL — universal grinding, light preload. Any two bearings of this designation clamped together produce the specified light preload with no shims.

What these specs mean in practice

The 15° contact angle is the speed-biased choice. A shallow angle keeps the ball from climbing the raceway shoulder, which reduces ball spin, friction and heat, so the bearing runs faster and cooler than the 25° (FAG suffix E) version of the same envelope. What you trade away is thrust capacity and axial stiffness. If your spindle’s limiting factor is rpm — high-speed milling, grinding, precision turning — 15° is right. If it is deflection under heavy cutting load, the 25° variant is the better tool.

The phenolic cage reinforces the same priorities. At roughly a fifth the density of brass it puts far less centrifugal load on itself at speed, and the laminate holds a small oil reserve that helps the bearing survive a brief lubrication interruption. In exchange it does not tolerate sustained high temperature, so lubrication needs to be clean and grease fills need to be light.

Light preload keeps friction and heat generation to a minimum. It is the standard choice for the majority of spindle positions; medium (UM) and heavy (UH) trade speed for rigidity.

Quantity and configuration

The UL suffix denotes a universally ground single bearing, and one bearing is what ships. Universal grinding is what makes that useful: two or more of these can be clamped into a back-to-back (DB) set for maximum moment stiffness and two-direction thrust, a face-to-face (DF) set where housing alignment is imperfect, a tandem (DT) set to double one-direction thrust, or a triplex stack. Each combination develops the specified light preload automatically. Buy one to replace a damaged half of an existing pair, or the matching count to build a complete set.

Fitting notes

Super precision bearings only deliver their accuracy on seats ground to match. Hold shaft journal and housing bore runout and roundness to a few microns and keep abutment faces square. Mount with controlled heat on the inner ring or a press acting only on the ring being fitted — never drive load through the balls. When building a set, keep the marked faces oriented as intended; reversing a bearing changes the preload and can turn a light-preload stack into a clamped one. Lubricate with a spindle grease or an oil mist or oil-air system sized for the bore and speed, and resist over-filling.

Interchange guidance

Same-envelope 15° super precision equivalents include NSK 7028C, SKF 7028 CD/P4A, NTN 7028C and Fafnir/Timken 2MM9128WI — the Fafnir 2MM prefix is 15°, which matches. Note that Fafnir 3MM9128WI and FAG B7028-E are the 25° versions of the same envelope; they share dimensions but not the contact angle, so they are carried here as dimensional cross-references rather than direct substitutes. The source designation B7028CA.P4.UL is retained as a searchable reference; the base identity, contact angle, cage and preload are as decoded above.