Practical answer
A FANUC-controlled machine can often be evaluated for an indexed external fourth axis, but “FANUC compatible” is not a complete technical conclusion. The exact CNC model, software version, machine-builder PMC ladder, available M-codes, I/O or communication resources, cabinet wiring and mechanical load determine what can be delivered safely.
This checklist is intended for 3+1 or 3+2 indexed positioning. If the rotary axis must move continuously with X, Y and Z during cutting, the project must be evaluated as a native interpolated-axis or dedicated simultaneous multi-axis application.
1. Record the complete machine and CNC identity
- machine builder, complete model, serial number and year;
- complete FANUC control model, not only the FANUC brand;
- software and version screens;
- machine electrical manuals, ladder backup or signal documentation when available;
- photographs of the control panel, handwheel and electrical cabinet.
The machine builder determines the PMC ladder, safety logic, M-code assignments and cabinet terminals. Two machines using the same FANUC control can therefore require different integration work.
2. Define the machining requirement before choosing hardware
Write down the real process:
- workpiece dimensions and weight;
- fixture weight and center of gravity;
- required indexing angles;
- maximum acceptable indexing time;
- cutting torque and tool direction;
- horizontal, vertical or dual-position mounting;
- production quantity and duty cycle;
- indexed positioning or simultaneous interpolation.
These inputs determine the rotary table, servo system, brake and controller architecture. Motor power must not be selected from the CNC brand or table diameter alone.
3. Confirm the command path
The design must state exactly how the FANUC machine requests an angle and how the external controller responds.
| Method | Best suited to | Checks required |
|---|---|---|
| M-code and digital I/O | Fixed-angle indexing and clear handshake sequences | Available M-code, output assignment, return input, timeout and alarm logic |
| RS232 or supported serial communication | Sending angle or program data when the machine supports the workflow | Port, protocol, data format, error recovery and program access |
| Ethernet or supported network communication | Projects requiring more flexible data exchange | Available interface, permissions, protocol and machine-builder implementation |
Do not select a communication method before confirming the exact machine configuration. A physical port does not guarantee that the required CNC or PMC function is available.
4. Define every handshake and interlock signal
| Signal or state | Purpose | Unsafe result if omitted |
|---|---|---|
| Index request accepted | Confirms that the external controller has started the requested cycle. | The CNC may wait indefinitely or issue repeated requests. |
| Rotary axis busy | Shows that positioning is in progress. | The machine may assume the table is already stationary. |
| In position | Confirms the requested angle is within tolerance. | Cutting may start at the wrong angle. |
| Clamp released | Allows rotation only after the mechanical clamp is open. | The servo may fight the clamp and damage the drive or table. |
| Clamp complete | Confirms the table is mechanically held before cutting. | Cutting may start without sufficient rigidity. |
| Servo ready / alarm | Blocks the cycle when the servo cannot operate correctly. | The program may continue with a faulted rotary axis. |
| Origin and limits | Supports reference return and safe travel. | Manual movement may exceed the permitted range. |
| Machine permission | Combines mode, door, emergency stop and safe-position conditions. | The table may move while the machine is not safe. |
| Cycle complete | Allows FANUC to resume the machining program. | The CNC may resume before positioning and clamping are complete. |
The FANUC program or PMC sequence should include a timeout. A missing completion signal must generate an alarm, not an automatic continuation.
5. Evaluate original-handwheel operation
The original FANUC machine handwheel can be retained only on compatible configurations. Confirm:
- access to the required handwheel, axis-select and multiplier signals or variables;
- clear separation between the external rotary axis and native machine axes;
- machine mode and safety permission for manual movement;
- servo-ready, clamp, origin and limit logic; and
- machine-builder wiring and PMC behavior.
If these conditions cannot be verified, use an independent handwheel. Never promise original-handwheel operation from the FANUC name alone.
6. Match the rotary table, servo and controller
Selection should treat the mechanical and electrical system as one package.
Rotary table
Confirm table diameter, center height, mounting direction, bore, fixture envelope, load, cutting torque, indexing accuracy, repeatability and clamp type.
Servo system
Calculate required torque, speed, inertia, acceleration, braking and duty cycle. Include the workpiece and fixture, not only the empty table.
Controller architecture
YD-1 uses a separate axis-card controller, matched servo drive and motor architecture, with no fixed servo-power range. CSD700 integrates the controller and servo drive and supports matched systems from 400 W to 1 kW.
Review the full comparison in YD-1 vs CSD700.
7. Build the automatic indexing sequence
- FANUC completes the current machining block and moves the tool to a safe position.
- The PMC verifies machine permission and sends the index request or angle.
- The external controller acknowledges the request.
- The rotary-table clamp is released and confirmed.
- The servo moves to the target angle.
- In-position status is confirmed within the specified tolerance.
- The table is clamped and clamp-complete feedback is verified.
- The external controller returns cycle complete.
- FANUC resumes the machining program.
Alarm recovery must define what happens if power is lost, the servo alarms, the clamp does not release, the table fails to reach position or the completion signal is lost.
8. Perform dry-run and cutting acceptance
- verify rotation direction and reference position;
- test every required angle without a workpiece;
- confirm spindle, tool, enclosure and fixture clearance;
- test clamp release and clamp complete;
- trigger servo, communication and timeout alarms;
- verify emergency stop and door response;
- check that manual movement is disabled in automatic cutting mode;
- run a complete dry cycle;
- machine a first article and inspect angular features; and
- record final parameters, I/O list and recovery procedure.
Common quotation mistakes
Quoting from “FANUC machine” only
The control and machine model are incomplete, so command method and PMC work cannot be defined.
Choosing the table from diameter only
Center height, fixture envelope, overhang, load, torque and clearance may make the selected table unsuitable.
Ignoring the clamp circuit
Position accuracy alone is not enough. Cutting rigidity depends on a correctly selected and confirmed clamp or brake.
Calling indexed 3+1 “simultaneous 4-axis”
These are different system architectures and should be quoted separately.
Information to send for assessment
- Machine nameplate and full model.
- FANUC control model and version screen.
- Control panel and handwheel photographs.
- Electrical cabinet and interface photographs.
- Available M-code, I/O, serial or Ethernet information.
- Rotary table, motor or drive information if already selected.
- Workpiece drawing, fixture, total load and center of gravity.
- Required angles, index time, accuracy and production cycle.
- Indexed or simultaneous machining requirement.
Use the CNC retrofit assessment form. Yidai will confirm the command path, interlocks, table, servo and supply scope before preparing a quotation.
Frequently asked questions
Can every FANUC machine use an external fourth axis?
No. Many machines can be evaluated, but compatibility depends on the exact control, PMC, interfaces, wiring and application.
Can the original FANUC handwheel always be retained?
No. It is possible only when the required signals, permissions and machine-builder logic are compatible.
Is M-code triggering enough by itself?
No. The design also needs accepted, busy, in-position, clamp, alarm, timeout and completion logic.
Can this system perform simultaneous four-axis cutting?
The standard external solution is for indexed positioning. Simultaneous cutting requires a native or dedicated multi-axis architecture.
