Fanuc AC Servo Motor A06B-1404-B904#F302 A06B1404B904#F302 AO6B-14O4-B9O4#F3O2

Fanuc A06B-1404-B904#F302 | Special Alpha i AC Spindle Motor Ai 2/10000 — 2.2/3.7kW, Flange, Slick Shaft, MZi

Part Number: A06B-1404-B904#F302

Type: AC Spindle Motor — Special Configuration

Series: Alpha i (αi)

Model: Ai 2 / 10000

Configuration: Flange Mount, Slick Shaft, MZi Speed/Position Sensor

Speed Range: 1,500 – 10,000 RPM

Input Voltage: 123–220 VAC, 3-Phase

Condition: New / Refurbished / Surplus

Overview

The Fanuc A06B-1404-B904#F302 is a special configuration Alpha i series AC spindle motor built on the Ai 2/10000 platform — 2.2 kW continuous, 3.7 kW duty-cycle, 1,500 to 10,000 RPM, flange-mounted with a plain slick shaft and MZi speed and position sensor.

The B904 base code and #F302 suffix together identify this as an OEM-specific variant: a motor built to a particular machine tool manufacturer's specification, with modifications to the standard Ai 2/10000 architecture that differentiate it from the catalogue B103 version.

What that "SPECIAL" designation means in practice is that this motor was engineered to a defined machine builder's requirement rather than off a standard production shelf.

The specific modifications covered by #F302 — which may include wiring configuration, connector type, special mechanical features, or additional interface requirements — were agreed between the machine builder and Fanuc at the time of machine design.

The electrical core of the motor is the same Ai 2/10000 platform that powers compact CNC machining centres, drill-tap centres, and small turning centres across the Alpha i generation: 2.2 kW continuous, reaching 3.7 kW in short-duty and cyclic operating modes, with a 10,000 RPM ceiling that enables the high surface speeds needed for productivity on aluminium, light alloys, and small carbide tooling.

Like the standard B103, the B904#F302 carries flange mounting, a slick shaft, and the MZi sensor — the three installation and functional characteristics that determine how this motor sits in its machine and what spindle control functions the CNC can access.

Key Specifications

What "SPECIAL" Means in the Fanuc Spindle Motor Context

Fanuc produces a proportion of its spindle motor output to OEM specifications — motors that share the same electromagnetic core as the standard catalogue model but carry specific modifications agreed with individual machine tool builders.

These modifications can range from connector type and wiring routing to mechanical features, paint, nameplate content, or additional interface provisions not present on the catalogue motor.

The A06B-1404-B904#F302 is in this category. The B904 part number identifies it as a non-catalogue special within the A06B-1404 series, and the #F302 suffix defines the exact special configuration. The implications for sourcing and service are significant.

For sourcing: the #F302 must be matched exactly when replacing this motor. The catalogue B103 shares the same electrical specification and physical platform, but may differ in connector configuration, wiring, or other details that the machine's cable harness and drive system were designed around. Installing a B103 in place of a B904#F302 without verifying compatibility at the machine interface level carries the risk of an installation mismatch that is not visible until the machine is powered up.

If only the electrical performance matters and the interface differences can be managed, a B103 can serve as a functional substitute — but this requires confirmed verification rather than assumed interchangeability.

For repair: the Ai 2/10000 spindle motor's core failure modes — bearing wear, winding insulation degradation, MZi sensor fault, and cooling fan failure — are well-understood by specialist spindle repair facilities regardless of the special configuration suffix.

A B904#F302 can be fully rebuilt using standard Ai 2/10000 parts and procedures. The #F302 modifications are typically external to the motor's rotating and electrical core, so the service scope is the same as for any Ai 2/10000 refurbishment.

Ai 2/10000 Platform — Power, Speed, and Application Range

The Ai 2/10000 base specification — 2.2 kW continuous, 3.7 kW short-duty, 1,500–10,000 RPM — defines the application space of the B904#F302 as firmly as the special configuration suffix does.

At 2.2 kW S1, this is a compact spindle motor for compact machine tools. The machines it was specified for are characterised by small working envelopes, high spindle speeds, and the need to machine aluminium, non-ferrous alloys, plastics, and lighter structural materials with efficiency and surface quality.

At 10,000 RPM, a 10 mm carbide end mill runs at a surface speed of around 314 m/min — solidly in the productive range for aluminium profiling on a compact machining centre.

The 1,500 RPM lower bound marks the base speed below which the motor operates in constant-torque mode rather than constant-power.

Below 1,500 RPM, the maximum available torque is maintained but power decreases proportionally with speed.

This region serves low-speed threading, tapping, and turning operations where torque rather than surface speed is the governing parameter. From 1,500 RPM to 10,000 RPM, the motor operates in its constant-power zone across the full working speed range.

The 78% power factor is consistent with this motor's 4-pole induction design at this power class.

It is a parameter that matters for drive cabinet sizing and input power supply capacity — the spindle amplifier's apparent power draw exceeds the actual output by the inverse of this power factor.

Slick Shaft — Correct for This Application

The slick shaft on the B904#F302 is a plain-bore coupling interface — no keyway, torque transmission by clamping force. At 3.7 kW peak output, the coupling arrangement that pairs with this shaft handles the transmitted torque without the positive mechanical engagement that a keyway provides on heavier motors.

The practical benefit of the slick shaft at 10,000 RPM is rotational balance.

A keyway introduces an asymmetric slot in the shaft surface — a geometric discontinuity that creates a small but real imbalance in the rotating shaft.

At lower speeds this is largely inconsequential, but at 10,000 RPM, imbalance contributions from the shaft and its drive element compound in ways that affect vibration amplitude at the spindle. The slick shaft presents a symmetric rotating surface, simplifying precision balancing of the shaft-coupling assembly.

The coupling component — whether a pulley, toothed sprocket, or direct coupling hub — must be installed with the clamping force specified by the coupling manufacturer, not estimated.

Under-torqued clamping allows the hub to walk under repeated starting and stopping loads, accumulating microslip that eventually manifests as fretting on both shaft and hub bore and produces progressive shaft runout.

MZi Sensor — The Spindle Function Enabler

The MZi at the rear of the motor provides the speed and position feedback that the Alpha i spindle amplifier needs to support the full set of spindle control functions.

Speed regulation — keeping the spindle at commanded speed under varying cutting load — is its continuous role. Oriented stop, Cs-axis operation, and rigid tapping are all dependent on the MZi generating clean, consistent position reference throughout the motor's operating life.

The MZi sensor assembly includes a sensing ring mounted to the motor shaft and a pickup head fixed in the motor housing.

The air gap between ring and pickup is a precision dimension — too wide and signal amplitude falls; too narrow and mechanical contact risk rises.

On motors returned from service, the air gap setting is one of the standard checks performed during disassembly inspection.

A gap that has changed from specification — whether through bearing wear, assembly error on a previous service, or mechanical damage — produces degraded sensor output that can present as speed instability, oriented stop failure, or Cs-axis alarm codes before the sensor is identified as the root cause.

Drive and CNC Compatibility

The A06B-1404-B904#F302 is compatible with Fanuc Alpha i spindle amplifier modules from the 6111, 6112, 6141, and 6142 series in the current class appropriate for 3.7 kW peak. It integrates with Fanuc CNC controls including Series 0i-B, 0i-C, 0i-D, 16i, 18i, and 30i/31i/32i.

The amplifier must carry the motor type parameter for the Ai 2/10000 and have the MZi sensor interface enabled.

Given the special configuration nature of the B904#F302, verifying the specific amplifier and cable interface requirements of the machine before ordering a replacement is a worthwhile step — the machine builder's documentation or the original machine configuration record will confirm whether the standard amplifier pairing applies or whether the special configuration includes amplifier-side variations.

FAQ

Q1: What does the "SPECIAL" designation (B904#F302) mean, and does it affect repairability?

The B904 base code identifies this as a non-standard OEM variant of the Ai 2/10000 spindle motor, built to a specific machine tool manufacturer's specification. The #F302 suffix defines the particular special configuration.

The special designation typically covers external features — connector type, wiring routing, mechanical interface details — rather than the motor's electromagnetic core or rotating components.

Repair facilities experienced with Alpha i spindle motors work with the same core components regardless of special suffix, so the B904#F302 is as fully repairable as the standard B103.

Q2: Can the standard A06B-1404-B103 be used as a direct substitute?

The B103 shares the same electrical specification — 2.2/3.7 kW, 1,500–10,000 RPM, flange mount, slick shaft, MZi sensor. However, the special modifications encoded in #F302 may affect connector configuration, wiring routing, or mechanical interface dimensions.

Before substituting a B103, verify the cable harness connector compatibility and any mechanical differences at the machine interface. If these are confirmed compatible, the B103 is electrically equivalent and will operate on the same amplifier with the same parameters.

Q3: What Alpha i spindle amplifier is required?

The Ai 2/10000 operates with Fanuc Alpha i spindle amplifier modules from the 6111, 6112, 6141, and 6142 series in the appropriate current class for 3.7 kW peak output. It integrates with Fanuc CNC controls including Series 0i-B, 0i-C, 0i-D, 16i, 18i, and 30i/31i/32i.

The amplifier motor type parameter must be set for the Ai 2/10000 and the MZi sensor interface enabled.

If the machine's drive was configured for the special B904#F302 configuration, confirm whether any amplifier-side parameters differ from the standard B103 setup before commissioning a replacement.

Q4: What spindle functions rely on the MZi sensor, and what happens if it fails?

Oriented stop, Cs-axis (spindle-as-axis) operation, rigid tapping, and real-time speed regulation all depend on the MZi. If the MZi produces degraded or intermittent output, these functions will generate alarms or fail to activate — speed instability during cutting, oriented stop failures at tool change, or rigid tapping synchronisation faults are the typical presentations.

MZi failure does not always manifest as an immediate, clear alarm; degraded sensor output often appears first as intermittent functional faults before progressing to a persistent alarm. If such symptoms appear, MZi inspection — air gap, sensor ring condition, and output signal quality — is the appropriate first diagnostic step.

Q5: What inspection steps are most important for a used A06B-1404-B904#F302?

Inspect the slick shaft end for fretting or scoring from improper coupling installation, and check for any runout introduced by previous coupling damage. Inspect the MZi sensor pickup and sensing ring at the motor rear for mechanical damage and verify the air gap is within specification.

Measure winding resistance across all three phases for balance and check insulation resistance to earth — the 78% power factor design means the motor's windings operate at moderate current, and insulation checks after coolant exposure or long storage are worthwhile.

Confirm the cooling fan operates freely. A bench run-up on a compatible Alpha i spindle amplifier at incremental speeds to 10,000 RPM, with MZi signal monitoring and current tracking, is the correct final verification before the motor is returned to production service.