SKFNN3011KMSPDouble-Row Cylindrical Roller Bearing 55 x 90 x 26 mm, 1:12 Tapered Bore, Machined Brass Cage, Super-Precision SP

Product Description

What this part is

An SKF NN 3011 KM/SP double-row cylindrical roller bearing, 55 mm bore x 90 mm outside diameter x 26 mm wide, built to super-precision tolerances with a 1:12 tapered bore and a machined brass cage. Two rows of cylindrical rollers in a 17.5 mm cross-section give 85.5 kN dynamic capacity and high radial stiffness — roughly three times the radial rating of a 6011 ball bearing in the same envelope. This is a machine-tool spindle and precision gearbox bearing.

Decoding the designation

NN — double row, three ribs on the inner ring, ribless outer ring. Radial load only, with axial displacement accommodated in both directions.
30 — ISO dimension series 30.
11 — 55 mm bore.
K — tapered bore, taper 1:12.
M — machined brass cage, roller-centred.
SP — SKF super-precision: ISO tolerance class 5 dimensional accuracy with class 4 running accuracy.

What these specs mean in practice

The 1:12 tapered bore is the working feature of this design. On a cylindrical NN bearing the tapered inner ring seats directly on a tapered spindle journal, with no adapter sleeve in the assembly. Drawing the ring up the taper expands it a measured amount, so radial clearance — or a light preload — is set by axial travel rather than by selecting a clearance class. That is how a spindle builder reaches a repeatable running clearance.

The ribless outer ring makes this the floating position in a two-bearing arrangement: the outer ring slides in its housing bore as the shaft grows with temperature, and axial location comes from a thrust or angular-contact bearing elsewhere in the shaft. The machined brass cage suits oil, oil-air and grease lubrication and tolerates the temperature excursions of a hard-worked spindle. Super-precision running accuracy pairs with tight fits: the shaft and housing seats carry the bearing’s accuracy through to the workpiece.

Published ratings and mounting data

Bore d: 55 mm — Outside diameter D: 90 mm — Width B: 26 mm
Basic dynamic load rating C: 85.5 kN
Basic static load rating C0: 96.5 kN
Limiting speed, grease: 6 700 rpm — oil bath: 8 000 rpm
Outer-ring raceway diameter EW: 81 mm
Chamfer r min: 1.1 mm — ra max: 1 mm
Shaft abutment da min: 61.5 mm — spacer sleeve abutment d1a min: 62 mm
Housing abutment Da: 83–83.5 mm
Rows: 2 — rolling element: cylindrical roller — open, no seals or shields
Bore taper 1:12 — cage: machined brass — tolerance class: SP
Mass: approx. 0.65 kg

Quantity and configuration

Sold as 1 Pc — one complete bearing: the ribless outer ring, and the tapered-bore inner ring carrying both roller rows and both cages. The bearing is separable into those two assemblies, which are a matched pair.

Fitting notes

Mounting is cold and clean, onto a tapered journal ground to the matching 1:12 taper. Inner-ring bore expansion is measured at each increment of drive-up, and radial clearance is checked between increments until the target figure is reached. The outer ring stays free to slide axially in the housing bore, which is what makes this the non-locating position. The tapered bore surface is a precision reference face: it stays free of nicks and burrs, since a high spot there reads as spindle runout for the life of the machine.

Interchange guidance

Same-specification equivalents at 55 x 90 x 26 mm with a 1:12 tapered bore and machined brass cage: FAG NN3011-AS-K-M-SP, NSK NN3011KM, NTN NN3011K, Koyo NN3011K, Nachi NN3011K, Rollway NN3011KM. Related sizes, not substitutes: the straight-bore NN 3011 M seats on a cylindrical journal and sets clearance by class rather than by drive-up; NNU 4911 in a comparable envelope carries its ribs on the outer ring and mounts the opposite way round; the single-row NU 1011 and N 1011 have a fraction of the radial stiffness. A commercial-tolerance NN3011K holds a different accuracy class from an SP bearing.