Adding a rotary 4th axis to an existing Fanuc 0i-MD or 0i Mate-MD machine is one of the most common upgrades we are asked about — it turns a 3-axis VMC into a machine that can index and contour on an A or B axis. The job has four parts: confirm the control can take another axis, install the amplifier / motor / cables, tell the CNC about the new axis (FSSB + servo + axis parameters), and give the PMC ladder the signals it needs. Below is the sequence we follow on 0i-D-generation controls, with the parameter numbers from Fanuc's 0i-D parameter manual (B-64310EN). Always keep a full parameter and ladder backup before you start.
1. Check the control can take a 4th axis
| 0i-MD | Up to 5 feed axes (4 simultaneous) + spindle. A 4th axis is within the standard axis count — usually only parameters are needed on the CNC side. |
| 0i Mate-MD | Standard 3 feed axes + spindle. A 4th feed axis is possible on most Mate-MD systems but needs the Fanuc option bit 1148#7 enabled and runs on βi amplifiers only. If 1148#7 is 0 on your control, the axis cannot be added by parameters alone — see the note at the end of this article. |
Also confirm the CNC option for rotary axis roll-over if you need 0–360° display, and polar coordinate / cylindrical interpolation only if you plan to program them. Pure indexing (A90., A180.) needs none of these.
2. Hardware you need
- Servo amplifier: on the 0i Mate-MD a βi SVM (e.g. A06B-6160-H00x / A06B-6164-H3xx) sized to the motor; on the 0i-MD either a βi SVM or a spare axis on an αi SVM. The amplifier sits on the FSSB optical fibre chain, so you also need one fibre cable (COP10A of the last amplifier → COP10B of the new one).
- Servo motor: a βiS or αiS motor with a 24 V brake is standard for rotary tables (shaft digit 3–5 in the A06B number) — the table must not creep when servos are off. Match the Pulsecoder type (αiA absolute is the normal choice) so no reference return is needed after power-up.
- Cables: motor power (with brake wires), Pulsecoder feedback (JF1 → motor), 24 V brake supply and relay, 200 V control power for the βi SVM, ESP / MCC wiring to the amplifier's CX29 / CX30 connectors, and the FSSB fibre.
- Rotary table: any mechanical table (Nikken, Kitagawa, Tsudakoma, local makes) with its gear ratio, clamp (hydraulic or pneumatic) solenoid and clamp-confirm switch. Note the ratio — you will need it for the feed-gear setting.
- Battery: absolute Pulsecoders need a battery — either the amplifier battery holder or a separate battery case on the motor cable.
Wire the amplifier into the emergency-stop chain exactly like the existing SVMs. Power up with the fibre connected and confirm the new amplifier's LED shows the normal ready state and no hardware alarm before touching parameters.
3. Tell the CNC how many axes it has
| 8130 | Number of controlled axes — set to 4 (set 1010 to 4 as well, or 0 to follow 8130). |
| 1020 | Axis name of the 4th axis: 65 = A, 66 = B, 67 = C. |
| 1022 | Axis attribute in the basic coordinate system — 0 (not one of the three basic axes). |
| 1023 | Servo axis number — 4 (must match the FSSB axis assignment below). |
Power the control off and on after changing 8130 — the CNC rebuilds its axis tables and the 4th axis appears on the position screen.
4. FSSB setting
Set parameter 1902#0 (FMD) = 0 for automatic FSSB setting, then open SYSTEM → FSSB. On the Amplifier screen the new SVM must appear in the chain with the correct amplifier type and max current; on the Axis screen assign the 4th axis to that amplifier slot and press (SETTING). If the amplifier does not appear, the fibre is reversed or not clicked in — alarm SV5136 "FSSB: number of amps is small" is the usual symptom.
5. Servo setting screen (motor initialisation)
Enable the screen with 3111#0 (SVS) = 1, then SYSTEM → SV-SET. For the new axis enter:
| Initial set bits | 00000000 (initialisation bit 1 cleared — the control initialises the motor on the next power-up) |
| Motor ID No. (2020) | From the motor's data sheet / nameplate table — e.g. βiS 4/4000 and βiS 8/3000 each have their own ID. A wrong ID gives SV0417 illegal servo parameter. |
| AMR | 00000000 |
| CMR (1820) | 2 (detection unit 0.001°) |
| Feed gear N / M | Table degrees per motor revolution ÷ 1000, reduced. Example: 1:90 table, 1 motor turn = 4° → N/M = 4000 / 1 000 000 = 1 / 250. Direct-drive with 1:1 = 360 000 / 1 000 000 = 9 / 25. |
| Direction (2022) | 111 or −111 — change the sign if A+ runs the wrong way (clockwise looking from +X toward the origin is A+ in the right-hand rule). |
| Velocity pulses / Position pulses | 8192 / 12500 for an αi/βi Pulsecoder on a semi-closed axis |
| Ref. counter (1821) | Pulses per motor revolution in detection units — e.g. 4000 for the 1:90 example (4° × 1000). |
Power off / on. If SV0417 or SV0301–SV0304 style alarms appear, re-check the motor ID and the N/M fraction; both must be integers after reduction.
6. Axis parameters for a rotary table
| 1006#0 ROTx | 1 — rotary axis |
| 1006#1 ROSx | 0 — rotary axis type A (coordinates roll over) |
| 1008#0 ROAx | 1 — roll-over function enabled |
| 1008#1 RABx | 0 = shortest direction in G90 absolute moves, 1 = follow the sign |
| 1008#2 RRLx | 1 — relative coordinates also roll over at 360 |
| 1260 | 360.000 — movement per rotation |
| 1320 / 1321 | Stored stroke limit — set to 99999999 / −99999999 for a continuous rotary; set real limits for a tilting (B) axis |
| 1420 | Rapid traverse (deg/min) — 3000–5000 is typical for a 1:90 table, check the table maker's rating |
| 1421 / 1423 / 1424 | F0 rapid override rate / jog feedrate / manual rapid rate |
| 1425 | FL rate for reference return (e.g. 300) |
| 1430 | Maximum cutting feedrate |
| 1620 / 1622 / 1624 | Acc/dec time constants — rapid / cutting / jog (100–200 ms to start, then tune) |
| 1815#5 APCx | 1 — absolute Pulsecoder fitted; 1815#4 APZx becomes 1 once the reference position is established |
| 1825 | Servo loop gain — 3000, same as the linear axes |
| 1826 / 1828 / 1829 | In-position width / positioning deviation moving / deviation stopped — copy from an existing axis to begin |
| 1851 | Backlash — measure with a dial indicator after the table is mounted |
| 1005#1 DLZx | 1 — reference return without a dog (absolute encoder: set position manually, see below) |
7. PMC ladder — the part people forget
The CNC will not move the axis until the PMC supplies the per-axis signals. Someone with the ladder tool (FANUC LADDER-III or the built-in PMC editor) needs to add:
- Interlock *IT4 (G130.3) — or set 3003#2 (ITX) = 1 temporarily to ignore per-axis interlocks while testing.
- Overtravel *+L4 / *−L4 (G114.3 / G116.3) — a continuous rotary has no limit switches, so either force them to 1 in the ladder or set 3004#5 (OTH) = 1 to ignore overtravel signals.
- Clamp / unclamp: M10 / M11 (or the builder's codes) driving the clamp solenoid, with the clamp-confirm switch feeding back to servo-off SVF4 (G126.3) so the servo releases while clamped and the table never fights the clamp.
- Brake control: the 24 V brake relay is normally released by the amplifier's MCC / servo-ready logic — never leave the brake permanently released.
- Detach function (optional): 1005#7 RMBx = 1 and 0012#7 RMVx let the operator remove the table and run 3-axis without servo alarms.
8. Reference position and first moves
- In JOG, with the clamp released, jog A+ and A− at low override. Correct the direction with 2022 if needed.
- Set the mechanical zero: for an absolute Pulsecoder set 1815#4 APZx = 0 → 1 at the desired position (power off / on when the control asks). Alarm DS0300 "APC alarm: need ref return" clears once APZ is set and the battery is good.
- Run G91 G28 A0. then G90 G0 A90. / A180. / A360. and confirm the display rolls over and the table returns to the same mark.
- Measure backlash and lost motion with a dial gauge on a known radius; enter 1851.
- Tune 1620 / 1622 downward only while the servo tuning screen shows no following-error overshoot and the motor stays cool.
Common alarms during a 4th-axis retrofit
| SV5136 | FSSB: number of amplifiers is small — fibre not connected / wrong direction, amplifier not powered, or 8130 set higher than the amplifiers present. |
| SV0417 | Illegal servo parameter — wrong motor ID, N/M not reducible, or initialisation bit not cleared. |
| SV0401 / SV0404 | V-ready off — ESP, MCC or 200 V control power not wired to the new SVM. |
| DS0300 / SV0300 | APC alarm: reference return needed — set APZ after the battery is fitted. |
| SV0410 / SV0411 | Excessive error at stop / in motion — brake not releasing, table clamped, or gear ratio (N/M) wrong by a factor. |
Important: Fanuc option 1148#7 (4th axis enable)
On many 0i-MD and 0i Mate-MD controls the 4th axis will not come alive even with every parameter above set correctly, because the CNC option parameter 1148 bit 7 is 0. This bit is a Fanuc option setting — it is not a user parameter and cannot be switched on from the MDI panel; it has to be enabled on the control itself.
Related guides
- How to identify a Fanuc servo motor — A06B order number decoded
- Setting the reference position / zero return on a Fanuc CNC
- Fanuc αi / βi servo amplifiers in stock
- Fanuc servo motors with brake (αiS / βiS)
- Fanuc Pulsecoders & batteries