FANUC SP9049 Alarm 49: Differential Speed Is Over Value

FANUC SP9049 means that, during differential spindle speed control, the speed received from the other spindle and converted for the local spindle exceeds the allowable motor-speed limit. The CNC may display SP9049 or SSPA:49 DEF. SPEED IS OVER VALUE, while the spindle amplifier displays 49.

FANUC calculates the converted differential-speed component by applying the active local spindle-to-motor gear ratio to the other, normally master-side, spindle speed. The correct response is to verify the commanded speed, motor-specific parameter data, active mechanical gear, and corresponding gear-ratio parameter. Do not increase a motor maximum-speed value merely to suppress the alarm.

For surrounding alarm numbers, see the FANUC Spindle Alarm Codes SP9034–SP9092.

What Does FANUC SP9049 SSPA:49 Mean?

Differential spindle speed control makes one spindle, called the slave or local spindle, rotate relative to another spindle, called the master or remote spindle. FANUC documents this function for applications such as rigid tapping at the center of a workpiece that continues rotating on the master spindle.

The slave-side control must translate the master-spindle speed into a speed meaningful for its own motor. If the slave spindle is connected to its motor through a gear train, the motor may need to rotate substantially faster than the spindle. A spindle speed that appears acceptable on the program screen can therefore become an excessive motor speed after conversion.

FANUC's 0i-D maintenance manual describes SP9049 as follows in practical terms:

• Differential speed mode is active.

• The speed of the other spindle is converted to the speed of the local spindle.

• The conversion applies the applicable gear ratio.

• The calculated value exceeds the allowable limit or maximum motor speed.

This is primarily a command-and-configuration range alarm. It does not, by itself, indicate a disconnected position coder, noisy feedback cable, defective spindle motor, or failed spindle amplifier.

How Differential Spindle Speed Control Affects Motor Speed

In a common differential rigid-tapping arrangement, the master spindle holds and rotates the workpiece at a constant speed. The slave spindle drives the tap. The slave-axis velocity is controlled relative to the master-spindle velocity so the tap has the required motion with respect to the rotating workpiece.

FANUC specifies two related limits that should not be confused:

1. Alarm 49 conversion check: the master/other spindle speed converted through the local slave-side gear ratio must not exceed the slave motor's maximum allowable speed.

2. Differential rigid-tapping operating limit: the sum of the master-spindle velocity and the slave-side rigid-tapping velocity command must not exceed the maximum speed of the slave spindle.

The first condition is the direct SP9049 definition. The second is a separate operating requirement that must also be checked when alarm 49 occurs during differential rigid tapping.

For a first-pass field calculation, the direct alarm condition can be screened as:

Converted master-speed component at the slave motor
= |master spindle speed| × |active slave motor/spindle ratio|

For example, if the master spindle runs at 2,400 min⁻¹ and the active slave-side ratio is 2.5 motor rotations per spindle rotation, the converted component is:

2,400 × 2.5 = 6,000 min⁻¹ at the slave motor

If the configured slave motor is allowed to run at only 5,000 min⁻¹, that operating point is invalid even though 2,400 min⁻¹ does not look high when viewed only as a spindle command.

This is a screening calculation, not a substitute for the exact FANUC and machine-builder calculation. Direction signs, the slave's own speed command, spindle selection, and machine-specific transmission arrangement also affect the complete operating state.

Why Parameters 4056–4059 Matter

On the FANUC systems covered by the applicable English parameter manual, parameters 4056 through 4059 define the ratio between the spindle motor and spindle for four possible gear states. The manual's first-spindle channel table selects them with the CTH1A and CTH2A input signals.

If the configured slave is another spindle channel, check that channel's corresponding CTH signals and spindle-parameter group. Do not assume that the A-channel signal names shown in the table apply to every master/slave assignment.

The standard scaling is the number of motor rotations for one spindle rotation multiplied by 100. A 2.5:1 motor-to-spindle ratio is therefore entered as 250. When parameter 4006#1 (GRUNIT) selects the higher-resolution increment system, the ratio is scaled by 1000 instead.

Do not assume that the number shown in 4056–4059 can be interpreted without first checking GRUNIT. A value of 250 represents 2.5:1 with the ×100 system but 0.25:1 with the ×1000 system.

The mechanical gear or clutch state must also agree with the CTH1A/CTH2A signals. All four parameter values can be numerically correct, yet the control can use the wrong one if the PMC reports an incorrect gear state or if a gear-change confirmation is missing or mistimed.

Parameter numbering is not universal across every FANUC generation. The cited B-65280EN/05 table uses 3056–3059 for Series 15i and 4056–4059 for the applicable 16i/30i columns. Older α-series documentation also lists 6556–6559 for certain controls. Use the English manual for the installed CNC and spindle software before editing any value.

1. Confirm the Exact Alarm and Operating State

Before changing the program or parameters, record:

• The full CNC message and 49 on the spindle-amplifier display

• The complete CNC series, spindle amplifier model, and spindle software series/edition

• Which physical spindle is the master and which is the slave

• The program block and commanded speeds active when the alarm occurs

• Whether the alarm appears when differential mode is selected, while the master accelerates, or when rigid tapping begins

• The selected mechanical gear on the slave side

• The applicable CTH1/CTH2 gear-selection states at the time of the alarm

• The exact slave spindle motor model and rated maximum speed

• Any recent motor, gearbox, spindle-amplifier, PMC, or parameter work

Confirm the number rather than diagnosing from the words “speed too high.” Standard spindle overspeed, differential speed, and spindle synchronization have different alarm numbers and calculation paths.

2. Check the Programmed Master-Spindle Speed

Review the executed program, not only the block visible at the cursor. Locate the command that establishes the master-spindle speed before differential mode is enabled. Also check macro variables, subprograms, spindle-speed overrides, constant surface speed, gear-selection M codes, and machine-builder cycles that may alter the effective speed.

Calculate the master-speed component at the slave motor using the active motor-to-spindle ratio. If it exceeds the verified motor limit, reduce the commanded master speed or select an approved operating gear according to the machine builder's process. Do not command the same high speed again merely to reproduce the alarm.

When differential rigid tapping is used, also verify the slave's rigid-tapping speed command. FANUC requires the master-spindle velocity plus the slave rigid-tapping velocity command to remain within the slave-spindle maximum. The master spindle must remain at a constant speed during the tapping operation; it must not accelerate or decelerate while the cycle is active.

Do not solve the problem by applying an arbitrary spindle override. The final commanded speed, gear state, tap pitch, feed relationship, and machine limits must remain valid for the entire entry, cutting, reversal, and withdrawal sequence.

3. Verify the Active Gear and Parameters 4056–4059

Use the machine electrical drawing and PMC diagnostics to identify the actual gear or clutch state and the corresponding CTH1/CTH2 inputs for the slave channel. Then compare the selected parameter with the real mechanical ratio.

Check for:

• A ratio entered for the wrong gear range

• Numerator and denominator reasoning reversed when the value was calculated

• A decimal-scaling error caused by the GRUNIT setting

• A 1:1 default value left in a machine that has a geared spindle

• A gear parameter copied from another machine with different pulleys or gearing

• Applicable CTH1/CTH2 signals that do not match the engaged gear

• An incorrect gear selection after PMC ladder, contactor, gearbox, or spindle work

• A parameter backup restored from a different spindle configuration

Do not simply reduce 4056–4059 until the alarm disappears. These values describe real machine mechanics. An intentionally false ratio can corrupt speed conversion and cause unexpected spindle behavior, including incorrect orientation or failure to stop as expected.

4. Confirm the Motor-Specific Spindle Parameters

The field advice to “confirm the spindle motor initialization parameters” is valid only when treated as a verification step. Compare the current spindle data with:

• The complete motor model and every suffix on the nameplate

• The exact spindle-amplifier and motor combination

• A verified machine backup or machine-builder commissioning record

• The applicable English FANUC Spindle Motor Parameter Manual, such as B-65280EN for the installed generation

• The specified maximum motor speed and motor-model data

In the cited parameter manual, parameter 4020 is the maximum motor-speed setting for applicable 16i/30i systems, with its standard value depending on the motor model. Other CNC generations can use a different displayed parameter number. The value must agree with the actual motor specification and any hardware-specific restriction.

Do not raise the maximum motor-speed parameter above the motor or spindle specification. That would conceal the calculation problem while removing a designed protection boundary.

5. Do Not Initialize Spindle Parameters Blindly

Parameter initialization can be appropriate after confirmed data loss, an incompatible amplifier replacement, or a motor change when the exact motor code and commissioning procedure are available. It is not the first universal remedy for SP9049.

Initialization can overwrite machine-specific settings for the motor, sensor, gear ratios, orientation, rigid tapping, speed limits, gains, and spindle options. Before any initialization:

1. Make a complete, readable backup.

2. Record the current spindle software series and edition.

3. Confirm the exact motor and amplifier models.

4. Obtain the correct initialization procedure and motor code from the applicable English manual.

5. Preserve and restore machine-builder values that are not part of the motor's standard data.

6. Compare the resulting parameters line by line before enabling spindle rotation.

If the machine operated correctly until one program, speed, or gear was changed, investigate that change before considering initialization.

6. Check Differential-Control Configuration Only When Relevant

On supported αi systems, the parameter manual identifies settings such as DEFFNC for enabling differential spindle speed control and DEFDRT for master-side feedback direction. These are configuration parameters, not routine alarm-clear controls.

Verify them only if the fault began after commissioning, option restoration, PMC work, or parameter loss. An incorrect polarity or sequence can create an unsafe or unintended relationship between the two spindles. Do not toggle these bits experimentally.

Also confirm that differential speed mode is being entered only in an allowed operating mode. FANUC documents it for speed control and rigid tapping, not simultaneously with Cs contouring, spindle synchronous control, or spindle orientation.

7. Retest at a Verified Safe Speed

After correcting the program, gear selection, or parameter data, start with a speed that has been calculated to remain comfortably below both the slave motor and slave spindle limits. Qualified personnel should monitor:

• Master-spindle actual speed

• Slave-spindle and slave-motor speed

• Active gear and CTH signals

• Entry into and exit from differential mode

• Rigid-tapping synchronization, reversal, and withdrawal where applicable

• Any new CNC or amplifier alarm

Increase speed only within the approved commissioning procedure. If a different alarm appears, diagnose that alarm separately rather than continuing to treat it as SP9049.

What Not to Do for SP9049

• Do not increase the maximum motor-speed value beyond the motor specification.

• Do not alter 4056–4059 merely to make the calculated speed smaller.

• Do not reinitialize all spindle parameters without a backup and exact motor data.

• Do not bypass gear-selection interlocks or force CTH signals.

• Do not continue high-speed testing after the calculation shows an invalid operating point.

• Do not replace the position coder, feedback cable, spindle motor, or spindle amplifier based on alarm 49 alone.

An encoder or amplifier problem should be investigated when its own alarm, unstable actual-speed data, or measured evidence supports it. SP9049 itself identifies an out-of-range calculated differential speed.

Difference Between SP9043, SP9049, and SP9050

For the feedback-signal fault, see the FANUC SP9043 Alarm 43 Differential Position Coder guide. Alarm 49 is not the correct reason to begin replacing the SP9043 feedback cable.

FANUC SP9049 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm SP9049/SSPA:49 on the CNC and 49 on the spindle amplifier.

2. Record the master and slave spindle assignments, commanded speeds, active program block, physical gear, applicable CTH1/CTH2 states, and exact motor model.

3. Multiply the master/other spindle speed by the active slave motor-to-spindle ratio and compare the result with the verified motor maximum.

4. If the result is excessive, reduce the programmed speed or select an approved operating gear.

5. Verify which of parameters 4056–4059 is active and confirm its value against the real transmission ratio.

6. Check the GRUNIT scaling and confirm that the actual gear or clutch state agrees with the CTH input signals.

7. Compare motor-specific data and the maximum motor-speed setting with the correct English FANUC manual and a known-good machine backup.

8. Initialize spindle parameters only if the data is proven missing or wrong and the exact procedure is available.

9. For differential rigid tapping, separately verify that the master speed plus slave tapping command stays within the slave-spindle limit and that the master remains at constant speed.

10. Retest at a calculated safe speed under the machine builder's procedure.

Technical References

• FANUC Series 0i-MODEL D / 0i Mate-MODEL D Maintenance Manual, B-64305EN/03, SP9049 / SSPA:49 alarm description

• FANUC AC Spindle Motor αi/βi Series Parameter Manual, B-65280EN/05, Differential Spindle Speed Control and spindle-to-motor gear-ratio parameters

• FANUC α Series Servo/Spindle Amplifier Maintenance Manual, B-65165E/02, Alarm Code 49 troubleshooting

All references above are English-language FANUC manuals. Always use the edition that applies to the exact CNC, spindle amplifier, spindle software, motor, transmission, and machine-builder configuration.

Need Help With FANUC SP9049 Alarm 49?

REACO CNC provides independent troubleshooting, testing, repair, compatibility checking, and replacement support for FANUC spindle systems. Send us the CNC alarm screen, spindle-amplifier display, complete CNC and amplifier models, spindle software information, master/slave assignment, motor nameplate, active gear, parameters 4056–4059, CTH signal state, and the program block that produces the alarm.

If testing identifies a drive-hardware requirement, browse FANUC servo, spindle, and power drives. For diagnostic assistance, visit the FANUC Technical Support Center or contact REACO CNC.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable speed limit, gear ratio, parameter number, calculation, and commissioning procedure depend on the exact CNC, spindle software, motor, gearbox, and machine.