Why You Get No Trigger on Probe After Full Movement and How to Fix It

It is the absolute worst feeling in the shop. You’ve spent twenty minutes setting up the workpiece, your G-code is verified, and you hit cycle start for the probing routine. The machine moves. The probe travels across the bed. It reaches the expected contact point, completes its full programmed stroke, and then... nothing. Silence. Then, the dreaded "Probe Open" or "Probe Fail" alarm hits the controller screen. Dealing with no trigger on probe after full movement isn't just a minor annoyance; it’s a production killer that usually points to a breakdown in the communication loop between your CNC controller and the sensing hardware.

Most machinists jump straight to the conclusion that the probe is dead. Honestly? It usually isn't. Probes from industry giants like Renishaw, Hexagon, or Blum are surprisingly rugged. They’re built to survive in environments full of flying chips and pressurized coolant. When a probe fails to trigger after it has traveled the full distance defined in your macro—like a G65 P9810 or G31 move—the problem is almost always tucked away in the settings, the interface, or a simple physical blockage you missed because you were in a rush.

The Logic Behind the Ghost Movement

To fix this, you have to understand what the machine thinks is happening. When you command a probing cycle, the controller sends a "skip" signal request. It tells the motor to move until it receives a 24V (usually) signal change from the probe interface. If the probe moves the full distance defined in the command—let's say 10mm—and that signal never changes, the software assumes the part isn't there or the probe is broken.

Think about the physical path. You have the stylus, the internal kinematic seat, the batteries, the optical or radio transmitter, the receiver mounted on the machine wall, the interface cable, and finally the I/O board on the CNC. A break anywhere in that chain results in a no trigger on probe after full movement.

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Sometimes the "full movement" part is the clue. If the probe actually touches the part but the machine keeps pushing until it alarms out, you have a signal transmission issue. If the probe never touches the part because the part is smaller than expected, you have a setup or macro issue. It sounds simple, but in the heat of a shift, people mix these up constantly.

Why Your Interface is Probably Lying to You

Communication is everything. Most modern shops use optical (infrared) or radio frequency (RF) probes. If you’re getting no trigger on probe after full movement, go look at your receiver first.

Check the LEDs. On a Renishaw OMM (Optical Machine Manned) receiver, you should see a green light when the probe is "on" and seated. If you see a red light while the probe is sitting still, the interface thinks the probe is already triggered. This is a "Probe Open" state. If the controller thinks the probe is already triggered, it won't "see" the new trigger when the stylus hits the part. It's essentially blinded by its own logic.

Batteries are the low-hanging fruit here. Don't just trust the "Low Bat" light on the screen. Lithium batteries used in probes can sometimes drop voltage just enough to stop the transmitter from working, but not enough to trigger a formal low-battery alarm on the CNC side. Swap them. It takes two minutes and saves you an hour of chasing ghosts in the wiring.

Macro Errors and the G31 Command

Sometimes the hardware is perfect, but the software is asking for the impossible. If you are using a Fanuc, Haas, or Heidenhain controller, your probing cycles rely on variables.

Look at your G31 or G65 block. If your Z or X value is too short, the probe will reach the end of its programmed path before it ever reaches the part. This technically results in a no trigger on probe after full movement because the "movement" was successfully completed without an interrupt signal.

• Check your Work Offsets: If your G54 is off by an inch, the probe is looking for a surface that isn't there.
• Verify the Search Distance: In Renishaw Inspection Plus, the Q value often defines the overtravel or search range. If Q is too small, the probe gives up too early.
• The "Start Position" Trap: If you start the probe too far away from the part, even a "full movement" won't bridge the gap.

I've seen guys spend all morning rewiring an interface only to realize the part was sitting 5mm lower in the fixture than the previous batch. The machine did exactly what it was told; it moved the full distance and reported that it found nothing.

Physical Interference and "Sticking" Stylus

Let's talk about the hardware itself. Probes use a kinematic seat—basically three pins resting on three pairs of balls. When the stylus moves, it lifts one of those pins, breaking the electrical circuit.

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If coolant has dried inside the probe body—which happens more often than people admit—the internal mechanism can get "sticky." If the pin doesn't lift cleanly, or if it's stuck in the "triggered" position because of gunk, the machine won't know what to do. You might get a no trigger on probe after full movement because the circuit never actually broke, or it stayed broken from the start.

Clean the stylus. Ensure there isn't a massive glob of thick grease or a stray chip wedged in the gap between the stylus holder and the probe body. It’s a precision instrument, not a sledgehammer. Treat it like one.

Infrared Line-of-Sight Blockage

If you’re using an optical probe (like an OMP40-2), line-of-sight is your biggest enemy. If a large fixture or a secondary spindle is blocking the path between the probe’s windows and the receiver, the "I'm hit!" signal will never reach the brain.

• Chip buildup: A pile of chips on the receiver lens is a common culprit.
• Coolant mist: Extremely thick coolant mist can sometimes scatter the IR signal, though this is rarer with modern modulated signals.
• Reflections: In very shiny stainless steel or aluminum setups, the IR signal can bounce off the walls and confuse the receiver.

If you suspect a line-of-sight issue, try rotating the probe in the spindle by 90 degrees. If the no trigger on probe after full movement error disappears, you know you had a blind spot in your signal transmission.

The Ghost in the Wiring: The Skip Signal

On the back end of the machine, there is a dedicated "skip" input. On a Fanuc, this is usually high-speed input X4.7. If the wire from the probe interface to the I/O board is frayed, or if a terminal screw has vibrated loose, the signal will never arrive.

You can test this by looking at the diagnostics page on your controller. Find the bit associated with the skip signal. Manually deflect the probe with your hand. Does the bit toggle from 0 to 1? If it doesn't move on the screen while you're moving the probe by hand, the problem is 100% electrical. It’s either the interface box, the cable, or the board.

Steps to Clear the Error and Get Running

When you're staring at the screen and the boss is walking by, follow this sequence to diagnose a no trigger on probe after full movement quickly:

1. Manual Trigger Test: Move the probe to a safe area. Activate it (M19 or the specific M-code for your machine). Manually deflect the stylus with your finger. Look for the lights on the probe and the receiver to change color.
2. Check the "Search" Distance: Look at your G-code. Is the Z-move actually long enough to reach the part? Add 10mm to the move and see if it catches.
3. Battery Swap: Just do it. Don't argue with the meter. New batteries eliminate a massive variable.
4. Clean the Windows: Wipe down the probe's glass ring and the receiver lens with a lint-free cloth.
5. Diagnostic Bit Check: Go into the CNC parameters/diagnostics and verify that the skip signal (G31 input) is actually toggling when the probe is triggered.
6. Review the Macro: If you recently updated your probing software or changed machines, ensure your M codes for turning the probe on and off are correct. An "off" probe will move its full distance and never trigger because its eyes are closed.

Nuance in Radio Probes

Radio probes (like the RMP60) are better for line-of-sight issues, but they suffer from frequency interference. If someone just installed a new high-powered Wi-Fi router in the shop or a new cell booster, it might be jamming the frequency. Most modern probes have a "Frequency Hopping" (FHSS) feature, but it isn't foolproof. If you get intermittent no trigger on probe after full movement errors, you might need to re-pair the probe to the receiver on a different channel.

Actionable Insights for Maintenance

To prevent this from happening in the middle of a hot job, implement a weekly probe check. This isn't just about calibration.

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• Monthly Battery Replacement: Don't wait for the alarm. If the machine runs two shifts, change them every 4-6 weeks.
• Inspect Stylus Integrity: A loose stylus can cause "chatter" in the signal, making the machine think it triggered when it didn't, or vice-versa.
• Air Blast Check: If your probe uses an air blast to clear the part before probing, ensure the nozzle hasn't moved and isn't blowing coolant into the receiver.

By systematically isolating the software (macro distance), the environment (line-of-sight), and the hardware (batteries and wiring), you can turn a three-hour mystery into a five-minute fix. Most of the time, the machine is just doing exactly what you told it to do—it's just that what you told it to do didn't match the physical reality inside the enclosure.