Needle-roller bearings

NTN's HK2016F uses a nominal 20 mm hardened shaft raceway when installed without an inner ring. The optional IR17×20×16.5 has a 17 mm shaft seat and a 20 mm raceway diameter. With the ring, the shaft supports its bore. Without it, the shaft surface runs directly on the rollers. Verify raceway properties, housing fit and clearance after mounting. HK2016F row on NTN B-40, physical page 100.

What makes a roller a needle roller?

Long, slender rollers provide a low cross-section and low inertia. NTN includes oscillating motion among their applications. NTN, Needle Roller Bearings, A-4, physical PDF page 8.

Load passes from the shaft or inner ring through the rollers to the housing. A cage assembly without rings uses both mating surfaces as raceways, while a drawn cup provides an outer raceway. NTN, A-4 and B-32, physical pages 8 and 92.

A thrust needle-roller arrangement has a different geometry. Its rollers lie radially in a flat cage between axial raceway surfaces, supporting axial load in one direction. NTN describes thrust assemblies with bearing washers or suitably prepared direct shaft/housing raceways. This axial load path is distinct from that of a radial needle bearing; the radial bearing's rating does not establish thrust capacity. NTN, B-242, physical page 302.

Drawn cups, machined rings and cages

These distinctions come from NTN, A-4, B-32, B-34 and B-56, physical pages 8, 92, 94 and 116. Removing a cage or adding an inner ring changes the arrangement; it does not supply a universal multiplier for load capacity, speed or life. The HCK full-complement description is not a second rating for an HK bearing.

The shaft can be a bearing raceway

A shaft serving directly as a raceway needs a bearing-quality surface, not merely a diameter that passes through the rollers. NTN specifies HRC 58–64 for a shaft or housing used as a raceway, together with an appropriate hardened depth. Its hardness discussion also describes a reduction of basic dynamic load rating when sufficient surface hardness cannot be obtained. Hardness alone therefore does not establish the original catalog rating or adequate support beneath the contact surface. NTN, A-16 and A-40, physical pages 20 and 44.

Geometry and finish have separate roles. NTN's recommended direct-raceway shaft accuracy is IT5, with IT4 shown for higher rotational accuracy; maximum roundness and cylindricity are IT3, or IT2 for that higher-accuracy case. Table 8.4 gives the surface-roughness notation 0.2a for shaft diameters of 80 mm and below. These are the catalog's raceway recommendations, distinct from its recommendations for an ordinary shaft seat beneath a separate inner ring. They are not measured properties of any particular shaft. NTN, A-40, Tables 8.3–8.4, physical page 44.

Alignment also affects the roller contact. NTN gives an inclination guideline of 1/2,000 for radial needle-roller bearings and 1/10,000 for thrust bearings, while explaining that the allowable inclination depends on bearing type, load and internal clearance. Even a small inclination can reduce life or damage the cage. These ratios are conditional design guidance, not self-aligning capability or universal assembly tolerances. NTN, A-40, Table 8.6, physical page 44.

Fits and clearance after installation

A thin drawn cup depends on the housing bore for its final form. NTN explains that the post-press-fit inscribed roller diameter depends on housing material and rigidity. For sufficiently rigid housings, its recommended fits give an inscribed diameter near the F8 range and approximately ordinary radial clearance. That statement does not define an exact running clearance for every material, wall thickness or temperature. NTN, B-35, physical page 95.

Free clearance, installed clearance and running clearance describe different states. Interference fits and temperature differences between inner and outer portions change the operating clearance; excessive negative clearance can generate heat and shorten life. The numerical clearance table on A-30 is specifically for machined-ring needle bearings, not a clearance table for every drawn cup. NTN, A-30, physical page 34.

The inspection fixture is another distinct condition. NTN evaluates drawn-cup inscribed diameter after pressing the bearing into a specified ring gauge. The gauge dimensions on B-36 characterize that inspection method; they are not substitutes for the installed housing fits on B-35. This matters because a loose, unmounted thin cup can be deformed without representing its supported working geometry. NTN, B-36, physical page 96.

Exact example: NTN HK2016F

The following example uses the open-ended, caged NTN HK2016F, without an inner ring. In this catalog, the suffix F identifies the Premium Shell construction. It is distinct from the neighboring closed-end BK2016 row, the longer HK2020F row, and sealed L/LL constructions. NTN, B-32 and B-40, physical pages 92 and 100.

All values in this table belong to the HK2016F row on NTN B-40, physical page 100. The dimensions are nominal except for the stated width tolerance; the mass is approximate. None is an inspection result. The derived nominal radial envelope is (26 − 20)/2 = 3 mm; this is neither the roller diameter nor the radial clearance.

For this no-inner-ring example, the arrangement is a nominal 20 mm hardened shaft raceway in a sufficiently rigid iron housing with nominal 26 mm bore. NTN's HK/BK fit table recommends N6 (N7) for an iron housing, R6 (R7) for a light-alloy housing, and h5 (h6) for the shaft without an inner ring. The parenthesized choices are printed alternatives; B-35 does not explain their selection. Its housing-bore recommendations include roundness and cylindricity of IT4 or less and maximum roughness notation 1.6a. These fit symbols describe tolerance zones, not an actual measured interference or installed clearance. NTN, B-35, Tables 1–2, physical page 95.

The optional inner ring changes the shaft interface

B-40 lists IR17×20×16.5 as the reference inner ring for HK2016F and identifies the bearing-plus-ring arrangement as HK+IR. The ring has nominal bore d = 17 mm, raceway diameter F = 20 mm with +0/−0.009 mm tolerance, and width B = 16.5 mm. Its footnote relates the raceway-diameter tolerance to ordinary clearance when combined with the corresponding no-inner-ring bearing. NTN, B-40 and B-131, physical pages 100 and 191.

This is an alternative 17 mm shaft-seat arrangement, not an extra ring fitted over the original 20 mm shaft. The roller raceway remains at nominal 20 mm, while the shaft now supports the ring bore. NTN's B-35 table prints k5 (j6) for the shaft with an inner ring. The ring's diameter tolerance and this shaft fit do not by themselves establish the complete operating clearance. NTN, B-35 and B-131, physical pages 95 and 191.

Dynamic rating, static rating and life are different quantities

NTN defines basic dynamic rating as the load corresponding to a basic rating life of one million revolutions: radial load for a radial bearing and axial load for a thrust bearing. Basic rating life has a 90% statistical rolling-fatigue survival basis for a group of identical bearings under identical conditions. It is not the guaranteed life of one bearing. NTN attributes this basic-life basis to ISO 281; this article does not establish compliance with the full standard. NTN, A-14, physical page 18.

For roller bearings, NTN gives:

L10  = (C/P)^(10/3)                     million revolutions
L10h = [10^6/(60 × n)] × (C/P)^(10/3)  hours

Here C and P are the applicable basic dynamic rating and bearing load in the same force units; n is constant rotational speed in min⁻¹. The hours equation is for constant-speed rotation. Oscillation has a separate treatment and is not equivalent to substituting an arbitrary rpm. NTN, A-14, equations 2.1 and 2.5, and A-16, physical pages 18 and 20.

Illustrative arithmetic, not an operating recommendation: assume the HK2016F direct-raceway arrangement above, a constant pure radial load P = 1,000 N, and n = 3,000 min⁻¹. Assume adequate raceway hardness and depth, geometry, housing support, clearance, lubrication and ordinary temperature, without adverse contamination. With C = 12,500 N, the ratio C/P = 12.5 gives:

L10  = 12.5^(10/3) = 4,532.8 million revolutions
L10h = 4,532.8 × 10^6/(60 × 3,000) ≈ 25,182 hours

These are derived basic fatigue-life quantities using the NTN model rating, B-40, and life equations, A-14. They are not measured service life, a maintenance interval or approval of the assumed installation. NTN separately discusses lubrication, contamination and temperature adjustments, and failures such as wear, corrosion and seizure are outside the basic rolling-fatigue calculation. NTN, A-14 and A-16, physical pages 18 and 20.

Static rating concerns deformation rather than that fatigue-life equation. NTN's roller-bearing definition uses calculated contact stress of 4,000 MPa and resulting permanent deformation approximately 0.0001 times the roller diameter. Its static safety factor is S0 = C0/P0,max. The catalog states a lower factor of 3 for ordinary NTN drawn cups and 2 for Premium Shell bearings, the category identified by this example's F suffix. Thus 19,200/2 = 9,600 N is algebra at that factor, not a universal allowable running load. Shock, accuracy requirements and the actual maximum static load remain separate influences. NTN, A-19 and B-32, physical pages 23 and 92.

Speed, lubrication and sealing limits

The HK2016F speeds above are conditional limiting speeds, not typical speeds or evidence of a tested duty cycle. NTN's basis includes correct mounting and appropriate internal clearance, a good-quality lubricant supplied and replaced at suitable intervals, ordinary operating temperature, and load P ≤ 0.09Cr. Limiting speed also depends on cage, dimensions, acceleration/deceleration, load, lubrication and cooling. NTN, A-36, physical page 40.

For the hypothetical load above, 0.09 × 12,500 = 1,125 N, so 1,000/12,500 = 0.08 meets that one load-ratio assumption. It does not establish the other speed conditions. The 8,000 and 12,000 min⁻¹ entries are not interchangeable merely because a bearing contains some lubricant. NTN, A-36 and B-40, physical pages 40 and 100.

Lubricant film separates rolling and sliding surfaces, reduces wear and frictional heat, and helps protect against corrosion. Seals retain lubricant and exclude water and foreign matter; their suitability depends on the operating environment and lubrication method. HK2016F is the open construction in this example. NTN's sealed L/LL drawn cups have their own grease and temperature conditions, and same-size sealed versions can have shorter rollers and lower ratings. Their limits are not automatically those of the open bearing. NTN, A-41, A-46 and B-32, physical pages 45, 50 and 92.

Evidence scope

The technical source is NTN's manufacturer-hosted Needle Roller Bearings catalog. Its cover prints CAT. NO. 2300-X/E and the copyright page prints 2011. The download URL contains 2300E_all.pdf; the file's 2020 modification metadata is not a printed technical revision date. Citations here identify printed A/B page numbers alongside one-based physical PDF pages. NTN, cover and copyright, physical pages 1 and 4.

This historical catalog example does not establish current-production specifications, cross-brand interchangeability, current-lot properties, or a customer's installed shaft, housing, lubricant or duty cycle. Actual operating clearance, temperatures, contamination, shock loading and raceway condition are unspecified here. The worked life and static-factor arithmetic illustrate the catalog relationships; they do not establish an application-wide load, speed or service-life envelope.