Nachi-Fujikoshi 1928: Bearings from Tools

Among the bearing enterprises founded in Japan in the early 20th century, Nachi-Fujikoshi occupies a distinctive position because its bearings grew out of machine tools and cutting tools rather than out of textiles or automotive hubs alone. The company dates to the late 1920s, when Japanese industry was building its own capacity for the tools that make other tools. That origin shaped a culture oriented toward precision, hardness and the working of hard materials, which in turn shaped the bearings it would produce. The result is a firm whose identity spans bearings, cutting tools, hydraulics and robotics, united by a common obsession with surface quality and dimensional accuracy.

This article explains why a tooling heritage is not a marketing footnote but a technical advantage, and it uses that thread to walk through the hardest bearing duty in general engineering - the machine-tool spindle - and the precision language that governs it.

1928: when cutting tools came before bearings

Machine tools and cutting tools sit at the base of every manufacturing chain. Before a country can mass-produce anything precise, it needs machines that can cut hardened steel accurately and tools that stay sharp while they do it. Firms that emerged in this sector developed unusual competencies: an understanding of tool and die steel, of heat treatment, of grinding and of the measurement of very small deviations. The company now known as Nachi-Fujikoshi grew from that foundation in the late 1920s, and bearings were a later branch of the same tree.

Those competencies transfer directly. A bearing ring is, in effect, a very carefully ground and hardened piece of steel, and the same grinding wheels, gauges and metallurgical knowledge that make a good cutting tool make a good raceway. A toolmaker moving into bearings therefore carries a natural advantage in the hardest part of the problem: holding a dimension and a surface finish that few others can reproduce in volume. The same pattern appears in Europe, where the Fischer grinding machine turned precision balls into the founding of FAG.

Why a toolmaker already knew how to grind

Grinding is where a bearing is really made. The geometry is fixed at the drawing, but the running quality, the noise and the life are set by how accurately and how smoothly the raceways are finished. A cutting-tool maker grinds hardened steel all day, to tolerances that a general machine shop never touches, and it treats a deviation of a few microns as significant rather than negligible.

That is why a tooling-first company can enter a demanding bearing segment without first building from nothing.

The spindle: the hardest general-engineering duty

A machine tool spindle is one of the most demanding bearing applications in existence. It must rotate a cutting tool or a workpiece at high speed while holding runout to a fraction of a micrometre, resisting cutting forces without deflecting, and dissipating heat without thermally distorting the machine. Bearing stiffness, precision and thermal behaviour determine the achievable accuracy of the parts the machine produces.

Runout measured in micrometres

Runout is the error that matters most. If the spindle axis wanders by even a micron as it turns, every surface the tool cuts inherits that error. The bearing therefore has to be accurate in ways that a general-purpose part is not, and its accuracy has to survive the preload and the fit that hold it in place. This is precisely the discipline a tooling culture already practises.

Preload is set cold

Spindle bearings are preloaded to remove all internal play and to raise stiffness. The setting is chosen at assembly, when the machine is cold, and it changes as the spindle warms because the shaft grows faster than the housing. A maker with metallurgical depth understands that shift and accounts for it; a maker that treats preload as a single number does not. The preload guide sets out the trade-off, and the angular contact range shows the matched-set forms.

Angular contact pairs and hybrid ceramic balls

Bearings for spindle duty are usually angular contact ball bearings arranged in matched sets. A single angular contact bearing takes thrust in one direction only, so pairs are used to carry combined radial and axial load and to locate the shaft. In the fastest spindles, hybrid ceramic bearings - steel rings with ceramic balls - reduce centrifugal loading on the outer ring and cut heat generation, which is what allows the speed to rise without the bearing skidding or overheating.

The families and classes involved are the tightest in the industrial catalogue. The relevant classes are the ones ISO 492 defines as P5 and P4, the load rating behind them is computed to a method such as ISO 281, and the boundary dimensions are shared under ISO 15. Our hybrid ceramic guide shows how the arrangement and the ball material interact, and the class comparison explains what each precision grade actually tightens. Spindle duty is described in the trade with a DN figure, the bore in millimetres multiplied by the speed in revolutions per minute, and a hybrid set can push that figure higher than an all-steel set of the same size.

A spindle of 70 mm bore turning at 15,000 rpm reaches a DN of just over one million, and at that point the contact angle and the ball material matter as much as the size. Steeper angles shift capacity from radial to thrust, which is why spindle sets are chosen as much by their angle as by their class.

Steeper contact angles trade radial capacity for thrust capacity.

From cutting tools to hydraulics and robotics

The portfolio broadened along a logic that is easy to follow. Cutting tools led to coatings and hard materials; hard materials led to hydraulics and precise machine elements; precise machine elements led to industrial robots and to the bearings those robots need. A robot arm is, in engineering terms, a chain of joints with reducers and bearings, and a firm that can make a machine tool can make the components of a machine that is essentially a movable machine tool.

Cycloidal and harmonic reducers: where the bearings sit

Industrial robots have become a defining application for high-precision bearings. Each articulated axis relies on a reducer, commonly a cycloidal or harmonic drive, whose internal bearings carry high torque at low speed. The reducer's own bearings take the eccentric and oscillating loads of the mechanism, while the output bearing must resist the overturning moment of the arm.

The output bearing carries the moment

A crossed roller or thin-section bearing at the joint output is what lets the arm carry a load at reach without the joint deflecting, and the robot's repeatability is limited by the play and stiffness of exactly those components. Collaborative robots add a further constraint: low backdrive torque and quiet running, so a human beside the machine is not endangered and the actuator can be finely controlled. That pushes the design toward low-friction, precisely preloaded bearings that a general-purpose part cannot match. Our robotics joint overview covers the joint by joint.

Surface finish is the quiet specification

Two properties dominate bearing performance: hardness, which resists fatigue and wear, and roundness, which controls vibration, noise and load distribution. Achieving both in volume requires controlled steel, controlled heat treatment and controlled grinding, and it requires measurement at a resolution finer than most machine shops ever need. A tooling heritage means the company was already invested in all three before it ever made a bearing.

The practical consequence is that surface finish is often the least visible and most decisive line on a drawing. Two bearings can share a designation and a load rating yet differ in the raceway finish that sets their noise and their grease life. The roller internal geometry section and the type selection guide both treat finish as a first-order variable rather than a detail, and our cylindrical roller range lists it where it matters.

The recurring mistakes in this area are consistent across the trade:

• Buying on the designation alone. Two bearings with the same number can differ in finish and internal clearance, which changes noise and life.
• Ignoring the preload shift. A preload set cold but never rechecked warm leads to either slack or seizure as the spindle grows.
• Using an all-steel set at high DN. Without the lighter ceramic ball, centrifugal load and heat rise faster than the speed does.
• Under-specifying the class. A normal class in a spindle position shows up as runout the machine cannot remove by any other means.
• Assuming a fit is enough. Spindle accuracy depends on the seat as well as the bearing, so the housing bore matters as much as the part.
• Trusting a logo over the process. A brand name does not by itself confirm grinding and measurement discipline at the plant that made the part.
• Splitting a matched pair. Two bearings of the same class do not share load automatically, and a factory-matched pair adjusted as a unit fails once its halves are swapped between positions.

What to ask a supplier of precision bearings

The lesson of a tooling-first bearing maker is that precision is a system property, not a single number. It depends on steel, heat treatment, grinding, assembly cleanliness, lubrication and measurement, and it degrades if any one of those is neglected. When selecting a bearing for a demanding application, it is therefore worth asking not only for the size and tolerance class but for the evidence behind the claimed performance.

Evidence beats heritage

For everyday industrial replacement, a standard bearing from a reputable maker is almost always the practical answer, and the specification reduces to size, clearance, seal and precision class. For spindle, robot and metrology applications, the tighter classes and the maker's process discipline genuinely matter. The questions that separate suppliers are therefore the same at every desk: which standard governs the tolerance, how is the rating computed, and what documentation travels with the part. Our technical section lists the standards that let you ask those questions precisely, the NACHI brand page lists the current ranges, and the industry pages show where precision duty concentrates.

The arc of a precision culture, read today

From a tool workshop in the 1920s to a portfolio spanning bearings, cutting tools, hydraulics and robotics, the arc is coherent rather than random. Each step preserved the same underlying demand: manufacture to a tolerance that few others can hold, and serve customers for whom that tolerance is the difference between working and failing.

That is why machine-tool heritage remains a meaningful signal in the bearing trade. It implies a culture that measures, that treats heat treatment as a science, and that takes grinding seriously. The bearing selector is the quickest way to move from an envelope to a shortlist once a class has been fixed.