Configuring Fanuc 18-M Repeat Runs During DNC Drip Feed

After a drip-fed cycle finishes, pressing Cycle Start on the Fanuc 18-M does not run the job again. The PC transmission has ended, the control has consumed the streamed blocks, and another cycle requires the sender and machine to be reset and armed again. The correction depends on whether the complete program can reside in CNC memory or must remain a DNC stream.

Where does the repeat path stop?

Follow the packet. The PC application reads the program file, transmits each block across the communications link, and the Fanuc 18-M consumes those blocks while operating in Tape mode. Once execution reaches the end of the transmission, both endpoints have changed state: the sender is at end-of-file, while the CNC no longer has the earlier blocks available for another pass.

Layer one first. A successful first cycle shows that the link can carry the program, but it does not prove that the sender and receiver can rearm for a second transmission. Record the installation-specific communication values from both endpoints rather than changing them while diagnosing the restart sequence.

Path item	PC/DNC side	Fanuc 18-M side	Passing check
Physical interface	Selected PC interface and cable	Connected CNC input interface	One complete program transfers without a communication alarm
Port or route	Port selected by easy DNC	Active input source	Data reaches the intended CNC input
Communication format and timing	Read configured values	Read matching configured values	No missing, corrupt, or stalled blocks
End state	Sender reaches end-of-file	Control completes the streamed cycle	Both endpoint states are recorded before any reset

Complete one uninterrupted first pass. If that fails, repair the physical or communication path before investigating repeat operation.

Which receive mode is active?

The decisive distinction is storage. In Tape mode, the control executes streamed blocks and releases earlier blocks from its working buffer. Cycle Start cannot restart a program whose beginning is no longer present. A branch or “go to” near the end has the same limitation: its target was consumed earlier in the stream.

Operating method	Where the full program remains	What happens after completion	Repeat requirement
Tape drip feed	PC file	CNC has consumed the preceding blocks; PC is at end-of-file	Rearm the receiver and retransmit from the PC
Memory execution	Fanuc memory	Program remains addressable by the control	Select the retained program and press Cycle Start again

Confirm the active operating mode at the control. If the job repeats when loaded into memory but fails only when streamed through Tape, the data path and NC program are functional; the missing function is coordinated stream restart.

Can the complete job run from CNC memory?

Use memory execution when the program fits. It directly matches the requirement for one completed part per Cycle Start because the control retains the program between runs.

1. Check the program size against the free memory reported by the control.
2. Transfer the complete program into CNC memory rather than starting a live Tape stream.
3. Select the stored program and verify that its normal end returns the control to a state from which Cycle Start can run it again.
4. Complete one cycle, then press Cycle Start without retransmitting the file.

If the file does not fit, the architectural choices are a memory upgrade or DNC software that can coordinate another transmission. Do not shorten or split the program until restart boundaries, modal state, offsets, and tool state have been reviewed; starting a fragment with inherited state can produce different motion from starting the complete program.

The check passes when the second memory-resident cycle begins without PC intervention.

Should M30 be replaced by M99?

M99 can repeat a program that remains in CNC memory, while M30 provides the ordinary completed-program boundary. These codes do not recover blocks already discarded during drip feeding. Placing M99 or a backward branch at the end of a Tape stream does not reconstruct the beginning of the file.

The requested behavior also matters. If the operator must press Cycle Start for every part, retain a completed-program boundary in a memory-resident program. Using M99 as a loop command can initiate another pass without the requested operator gate; its exact main-program behavior must be checked on the control configuration before production use.

1. Test the selected end code with motion inhibited or under the site’s controlled proving method.
2. Observe whether the control stops at the end, returns to the program start, or immediately repeats.
3. Select the behavior that preserves the required operator action between parts.

The check passes only when one Cycle Start produces exactly one intended cycle.

How should the DNC sender restart the stream?

When the program must remain on the PC, repetition becomes a two-endpoint state problem. The sender must return to the first block, and the Fanuc must be in Tape receive-ready state before retransmission begins. Repeating bytes continuously is not enough if the CNC is still in its completed or reset state.

Inspect the documentation and settings for the installed easy DNC version for a documented repeat, retransmit, queue, or cycle-restart function. Setting names and behavior vary by DNC application, so use the function described by that software rather than assuming an M99 in the NC file controls the PC.

Observed stop	Stopping point	Required correction	Proof
PC remains at end-of-file	DNC application	Configure its documented restart or automated resend workflow	The sender returns to the first block without manual file reopening
PC restarts but CNC accepts nothing	CNC receive state	Place the control in the required Tape receive-ready state before transmission	The first block of the new pass is accepted
Both endpoints require manual reset	Coordination between endpoints	Use cycle-aware DNC software or revise the operating procedure	Sender and receiver rearm in the correct order
No suitable sender function exists	DNC capability	Use different DNC software or add CNC memory	A second cycle starts without manually resending the file

The check passes when the sender is ready at the first block and the control is ready to accept it before Cycle Start.

How is the complete repeat sequence verified?

1. Record the selected operating mode, input source, DNC file, and communication settings.
2. Run one complete cycle under the machine’s controlled commissioning conditions.
3. At program completion, do not reset the PC, reopen the file, or manually reselect receive mode.
4. Press Cycle Start once.
5. Confirm that transmission begins at the first program block, the CNC accepts it without a communication alarm, and the second cycle follows the same programmed path.
6. Stop after the second completion and confirm that no unintended third cycle starts.

If the PC does not leave end-of-file, correct the sender workflow. If the PC transmits but the CNC does not accept the first block, correct the receive-ready sequence. If both endpoints restart but execution begins at the wrong location, correct the file-start or program-selection workflow.

FAQ