Siemens SINUMERIK codes
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Siemens SINUMERIK Controller

Spindle · Intermediate · 30-120 minutes

Alarm 16751

Siemens 840D 16751 - Channel block spindle/axis SPCOF not executable

ALARM 16751 fires when an SPCOF (Spindle Position Control Off) command is attempted on a spindle that is not in open-loop control mode, or when position control cannot be safely deselected in positioning/axis mode. This typically occurs due to incorrect spindle operating mode configuration, active position control loops, or conflicting spindle function blocks in the NC program.

Siemens SINUMERIKSpindleIntermediate30-120 minutes

16751

Siemens 840D 16751 - Channel block spindle/axis SPCOF not executable

Channel block spindle/axis SPCOF not executable

Siemens SINUMERIK 840D alarm 16751: Channel block spindle/axis SPCOF not executable. This alarm indicates a program or channel-level error on the SINUMERIK control. The part program or machine function cannot be executed as commanded.

Root Cause Summary

ALARM 16751 fires when an SPCOF (Spindle Position Control Off) command is attempted on a spindle that is not in open-loop control mode, or when position control cannot be safely deselected in positioning/axis mode. This typically occurs due to incorrect spindle operating mode configuration, active position control loops, or conflicting spindle function blocks in the NC program.

Safety

  • Refer to Siemens documentation
  • Ensure qualified technician performs repairs

Causes and Fixes

  1. 1

    Access SINUMERIK NCK Parameter menu: Main → Parameters → Machine Data (MD) and search for MD 37000 (SPIND_MODE_MASK) for the affected spindle.

  2. 2

    Verify spindle mode bits: confirm spindle is not in positioning mode (bit 0) or axis mode (bit 1). If active, coordinate with machine builder to understand intended spindle configuration.

    Do not modify machine data without understanding application requirements; incorrect spindle mode can cause uncontrolled rotation.

  3. 3

    Check MD 37010 (SPIND_CTRL_TYPE): if set to closed-loop control, the spindle speed control is active and SPCOF cannot execute. Program must first switch to open-loop mode or remove speed control commands before SPCOF.

  4. 4

    Review NC program block %2: confirm SPCOF is not issued immediately after S-function spindle speed commands; insert appropriate dwell (G04) or spindle stop (M5) before SPCOF if needed.

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