SKFNN3034KMC481Super Precision Double Row Cylindrical Roller Spindle Bearing 170x260x67 mm, 1:12 Tapered Bore, Brass Cage, C1 Clearance

Product Description

What this part is

An SKF NN 3034 KMC/C481 super-precision double-row cylindrical roller bearing, 170 mm bore x 260 mm outside diameter x 67 mm wide, with a 1:12 tapered bore, a machined brass cage and an annular lubrication groove with three radial holes in the outer ring. This is a large machine-tool spindle bearing: 457 kN dynamic capacity and roughly 2 000 N/µm of radial stiffness in a 45 mm cross-section, which is a combination no ball bearing can approach.

Decoding the designation

NN — double row, three ribs on the inner ring, no ribs on the outer ring. The bearing therefore accommodates axial displacement in both directions.
30 — ISO dimension series 30 (medium section).
34 — 170 mm bore.
K — tapered bore, taper 1:12.
M — machined brass cage, prong type, roller-centred.
C481 — SKF special-execution suffix; the bearing is built to that special specification rather than the plain catalogue SP variant.

Internal clearance is C1 (reduced) as standard for this family, and the outer-ring lubrication feature is the same annular groove and three holes that SKF also designates W33.

What these specs mean in practice

The tapered bore is the whole point of the K suffix. Drawing the inner ring up a tapered spindle seat or an adapter/withdrawal sleeve expands it a controlled amount, so you set radial clearance — or a light negative clearance, i.e. preload — by measured axial travel. That is how a spindle builder hits a target running clearance repeatably. A straight-bore NN 3034 cannot do this and is not a substitute on a tapered seat.

Because the outer ring has no ribs, the bearing is non-locating. It carries radial load only. Axial location has to come from a thrust or angular-contact bearing elsewhere in the spindle; this bearing will not hold the shaft in position and must not be asked to.

C1 clearance and super-precision running accuracy mean it is intolerant of sloppy fits: an out-of-tolerance seat or an oversize housing bore consumes the clearance and the bearing runs hot. The machined brass cage suits the oil, oil-air or grease lubrication typical of large spindles and tolerates the temperature excursions.

Published ratings and mounting data

Basic dynamic load rating C: 457 kN
Basic static load rating C0: 815 kN
Fatigue load limit Pu: 83 kN
Attainable speed, grease: 3 200 rpm — oil: 3 600 rpm
Bore d 170 mm — OD D 260 mm — Width B 67 mm
Inner-ring shoulder diameter d1: 204 mm — outer-ring raceway diameter E: 236 mm
Lubrication groove width b: 8.9 mm — hole diameter K: 4.5 mm — nozzle position dn: 230.8 mm
Chamfers r1,2 min 2.1 mm — r3,4 min 1.1 mm — ra max 2 mm
Shaft abutment da min 181 mm — housing abutment Da 238–249 mm
Permissible axial displacement s: 2.5 mm max
Radial internal clearance C1 — bore taper 1:12 — rows 2 — open, no seals
Reference grease quantity: 105 g — Mass: approx. 12 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 brass cages. It is separable, so it comes apart into those two assemblies. They are a matched set and belong together.

Fitting notes

Mount cold and clean. Measure the inner-ring bore before and radial clearance after every increment of drive-up; do not chase a number by feel. The lubrication holes in the outer ring must line up with the housing feed, and the outer ring must be free to slide axially in its bore — that freedom is what makes it the floating bearing in the spindle. Handle the tapered bore carefully: a burr on the taper is a high spot that shows up as spindle runout for the life of the machine.

Interchange guidance

Dimensionally interchangeable with 170x260x67 mm double-row tapered-bore cylindrical roller spindle bearings: SKF NN 3034 K/SPW33, FAG NN3034-AS-K-M-SP, NSK NN3034K, NTN NN3034K, Nachi NN3034K, Koyo NN3034K. Confirm the tolerance class and clearance before ordering — a P0 commercial NN3034K is not a substitute for a super-precision unit in a spindle. Related sizes are not substitutes: the straight-bore NN 3034 will not set clearance on a tapered seat; NNU 4934 in a similar size class carries its ribs on the outer ring and mounts entirely differently; and a single-row NU 1034 or NU 234 has far lower stiffness. The C481 special execution should be matched if the machine builder specified it.