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CNC axis following error (excess error)

Technical review pending. This guide is based on the cited manufacturer documentation; check it against the manual for your exact model and firmware before acting.

A following error alarm means an axis fell too far behind where the control commanded it to be. Every control has one: FANUC SV0411 (moving) and SV0410 (stopped), Haas 103 AXIS SERVO ERROR TOO LARGE, SINUMERIK 25050 contour monitoring and 25040 standstill monitoring. The alarm says the axis could not follow; when and where it happens tells you why.

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Where it shows up

Likely causes and how to tell them apart

1Mechanical binding, crash damage or chips

Points to it
One axis; same position each time or after a collision; rough when jogged slowly.
Check
With the axis locked out, check ways, way covers, ballscrew, coupling and bearings for binding.

2Motor brake not releasing

Points to it
Vertical or braked axis; alarm on the first move after servo-on.
Check
Check brake supply and release (Haas: 20–30 VDC across the brake leads after RESET, none in E-stop).

3Power or encoder cable fault

Points to it
Intermittent; at positions where the cable flexes; comes with encoder, short-circuit or ground-fault alarms.
Check
Inspect connectors and test the cables; insulation-test motor and cable only with them disconnected from the amplifier.

4Load or acceleration beyond the axis

Points to it
Only in heavy cuts or fast rapids; overload alarms (FANUC SV0436, Haas 108) in the history.
Check
Compare the position error or load during the move with the limit; review feeds, cut depth and acceleration.

5Amplifier dropped out

Points to it
An amplifier alarm (FANUC SV0401, Haas 161, SINUMERIK 25201) comes with the following error.
Check
Fix the amplifier or drive alarm first; the following error is a consequence.

6Tuning or limit parameters wrong

Points to it
Started after a parameter load, motor change or tuning session.
Check
Compare gains and following-error limits with the builder’s backup before changing anything.

Diagnostic sequence

  1. Read every alarmNote the axis and any amplifier, encoder or overload alarms logged at the same time; those usually come first.
  2. Moving or stopped?Moving (FANUC SV0411, SINUMERIK 25050, Haas 103 during a move) points to load, binding or tuning; stopped (FANUC SV0410, SINUMERIK 25040) points to gravity, brakes, clamps or external force.
  3. When in the move?First move after servo-on: brake. Same position every time: mechanics or a flexing cable. Only at high speed or heavy cut: load, acceleration or limits.
  4. Watch the errorUse the control’s position-error display (FANUC DGN 300, the axis load display on Haas, a trace on SINUMERIK) on a slow and a fast move.
  5. Check mechanics before parametersWidening the following-error limit hides a mechanical problem; only the machine builder should change it, and only after mechanics, brake and cables are cleared.

Evidence to collect

Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.

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