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Understanding Fanuc Parameter 1860: Reference Position and Absolute Encoders

Fanuc Parameter 1860 stores the absolute position of an axis within the current rotation of the encoder. It is a critical, read-only system parameter used by the CNC to track exactly where an axis is relative to its reference (home) position. If the value in Parameter 1860 is lost or incorrect—often due to a battery failure—the machine will lose its "sense" of where it is, leading to homing alarms. What is the Function of Parameter 1860?

In Fanuc CNC systems, Parameter 1860 acts as the machine's memory for axis position data when using absolute pulse coders (APC). Unlike incremental encoders, which must hit a "limit switch" or "dog" every time the machine starts up, absolute encoders always know their position.

Role in Homing: When an axis is successfully homed (set with Parameter 1815.4 APZ), the current encoder count is saved into Parameter 1860.

Data Type: It typically uses modular arithmetic, meaning the value "wraps around" based on the encoder's pulses per revolution.

Reference Completion: If the system detects a discrepancy between the physical position and the value in 1860, it may trigger a "Request for Reference Position Return". How Parameter 1860 Works During Startup

When you power on a Fanuc machine equipped with absolute encoders:

Verification: The CNC reads the current value from the encoder.

Comparison: It compares this value against the stored data in Parameter 1860.

Validation: If they match within a certain tolerance, the machine "remembers" its position immediately without requiring a manual zero return. Troubleshooting Common 1860 Issues

Most issues related to Parameter 1860 arise after a battery failure or motor replacement.

Alarms 300-349 (APC Alarms): These indicate that the absolute position data has been lost.

Reference Position Incomplete: If you reset Parameter 1815 but the machine doesn't move to the correct spot, the value in 1860 will often change automatically once a new reference point is established. fanuc parameter 1860 work

Soft Overtravel Alarms: If the stored position in 1860 suggests the machine is outside its travel limits upon startup, you may need to power on while holding "P" and "CAN" (Cancel) to bypass the check and re-home the axis. Step-by-Step: Setting the Reference Position

Because Parameter 1860 is a system-generated value, you do not "type in" a value manually. Instead, you perform a procedure to let the CNC update it:

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Fanuc Parameter 1860 is a critical coordinate system setting that manages the relationship between the machine’s mechanical zero and its absolute position detection system. This parameter is specifically used on machines equipped with absolute pulse coders (APCs) to ensure the control always knows exactly where the tool is, even after a power cycle. Core Function and Purpose

Parameter 1860, along with its counterpart Parameter 1861, defines the reference position for each axis. When an absolute encoder is used, the CNC must know the offset between the encoder's "internal zero" and the physical machine zero.

Coordinate Alignment: It tells the CNC how to calculate the machine coordinate value from the pulse data provided by the absolute encoder.

Reference Return (Zero Return): Unlike incremental systems that require a physical trip to a limit switch (homing) every morning, systems using Parameter 1860 "remember" their position. This parameter stores the necessary data to maintain that reference. How Parameter 1860 Works in Practice

In most modern Fanuc controls (such as the 0i, 16i, 18i, and 21i series), the process of setting this parameter is often automated during a zero-point establishment procedure.

Detection System: For this parameter to be active, Parameter 1815 #5 (APC) must be set to 1 (indicating an absolute pulse coder is in use).

Home Position Setup: When you perform a manual zero return to set the home position, the CNC calculates the difference between the current encoder reading and the desired machine zero.

Automatic Update: Once the APZ (Parameter 1815 #4) bit is toggled to 1 following a restart, the CNC often updates 1860/1861 automatically to reflect the precise physical location of the axis. Troubleshooting and Maintenance

If your machine loses its home position (common after a battery failure or encoder replacement), you will likely see a 300 APC Alarm. To fix this: Motor Replacement: Swapping an old motor for a

Enable Parameter Writing: You must set PWE (Parameter Write Enable) to 1 on the SETTING screen to make changes.

Manual Adjustment: While usually updated by the system, technicians may manually adjust Parameter 1860 to "shift" the machine zero without physically moving the encoder or motor.

Scale Synchronization: On axes with separate linear scales that do not hold rotation data, Parameter 1815 #6 (NRT) determines if the reference position is updated when coordinates pass the value stored in 1860. Related Parameters for Work Offsets

While 1860 handles the machine's "foundation" coordinates, operators use different tools for daily job setups:

G54–G59: These work coordinate systems (WCS) are offsets relative to the machine zero established by 1860.

Parameter 1201–1202: Often used for manual absolute settings that affect how the absolute position display behaves during tool changes or G43 height compensations.

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FANUC Parameter 1860 is a critical axis-specific parameter used to store the absolute position data (machine coordinate) of an axis equipped with an absolute pulse coder (APC).

When a machine is equipped with absolute encoders, it does not need to be homed every time it is powered on because the CNC "remembers" the current position by reading the value stored in this parameter. Core Function and Mechanics

Data Storage: This parameter holds the current machine coordinate value for each axis. When you power off the machine, the encoder's battery keeps the internal pulse count active. Upon restart, the CNC compares the encoder's data with the value in Parameter 1860 to re-establish the absolute position without physical movement. Interaction with Parameter 1815:

Bit 5 (APC): If set to 1, the CNC knows the axis has an absolute encoder.

Bit 4 (APZ): This is the "Reference Position Established" flag. When this bit is 1, the CNC considers the value in Parameter 1860 to be valid and synchronized with the physical machine position. When Does It Change? G99 G01 Z-50.0 F0.2 )

Automatic Updates: During normal operation, the CNC constantly updates this value as the axis moves.

Homing/Zero Return: When you perform a manual reference position return, the system sets the current physical position as the "zero" point and updates Parameter 1860 accordingly while flipping 1815#4 (APZ) to 1.

Loss of Position: If the encoder battery dies or the encoder is disconnected, the system loses the synchronization between the mechanical position and Parameter 1860. This triggers a 300 APC Alarm, requiring you to re-set the reference position. Setting or Resetting Procedure

If you lose your home position (e.g., after a battery failure), you must re-synchronize Parameter 1860. You can find detailed technical guidance in the official PARAMETER MANUAL. A typical reset involves: Enabling Parameter Write (PWE = 1).

Setting Parameter 1815 Bit 4 (APZ) to 0 for the specific axis.

Jogging the axis to the physical home position (often marked on the machine). Setting Parameter 1815 Bit 4 (APZ) back to 1.

Powering the machine off and back on to finalize the new position in Parameter 1860.

Important Safety Note: Because Parameter 1860 defines where the machine "thinks" it is, an incorrect value can cause soft overtravel alarms (e.g., Alarms 500 or 501) or, worse, a physical crash. Always verify your coordinates after modifying this parameter.

Are you currently dealing with a 300 APC Alarm on a specific axis? How to Enable Parameter Write Enable (PWE) on a Fanuc CNC

2. When do you need to change it?

You typically only touch this parameter during:

1. Motor Replacement: Swapping an old motor for a new one with a different encoder.
2. Scale Replacement: Replacing a linear glass scale with a different resolution model.
3. Retrofitting: Installing a new CNC control on an old machine.
4. Pitch Error Compensation Failure: If the machine consistently drifts or cannot finish the pitch error compensation cycle.

Best Practices for Managing FANUC Parameter 1860

1. Document the baseline. Before any mechanical maintenance, record Parameter 1860 and 1861 values.
2. Use a consistent test piece. Keep a standard aluminum block with a pre-drilled hole for rigid tapping validation.
3. Consider temperature. Machine warm-up affects spindle expansion. Always set Parameter 1860 after the spindle has been running for 20 minutes at typical operating speed.
4. Combine with servo parameters – In multi-axis machines, Parameter 1860 works in tandem with servo parameters 2021–2024 (for C-axis synchronization). Misalignment in either will cause errors.

3. Parameter Details

| Parameter Number | Data Type | Unit | Valid Range | | :--- | :--- | :--- | :--- | | 1860 | Word Integer (2-byte) | Percentage (%) | 0 – 100 (or higher depending on specific Fanuc Series/Option) |

• Typical Setting: 100 (Disables override increases; locks feed at 100%).
• Default Setting: Often set to 150 or 200 by machine tool builders (MTB).

Prerequisites

• FANUC Series 0i, 15i, 16i, 18i, 21i, 30i, 31i, or 32i control (Parameter 1860 exists on most, but confirm in the manual)
• A known good reference tool or dial indicator with magnetic base
• MDI mode access
• Parameter write enable (set PWE = 1)

Guide: Fanuc Parameter 1860 (Feed per Revolution Override)

1. What is Parameter 1860?

Parameter 1860 controls the Feed per Revolution (FPR) Override limit.

When your G-code program commands a feed rate based on spindle revolutions (e.g., G99 G01 Z-50.0 F0.2), the operator can adjust this feed rate using the Override knob on the control panel (usually 0%, 10%, ..., 150%, 200%).

Parameter 1860 sets the maximum percentage of override the operator can select. Any override selection higher than this parameter’s value will be ignored or clamped to this maximum.