How to add 4th axis on Fanuc?

First, we must determine whether our existing CNC machine can support the addition of a 4th axis. Currently, commonly seen Fanuc systems on the market include the 0 series, 0i-A series, 0i-B series, 0i-C series, 0i-D series, and 0i-F series. Due to their age, machines with 0, 0i-A, and 0i-B systems generally have little value for retrofitting and will not be discussed here.

So let’s take a look at the table below to see if your machine can support the addition of a 4th axis:

No.	System	4th Axis Addition	Remarks
1	0i-MC	Yes
2	0i-MATE-MC	No
3	0i-MD	Yes
4	0i-MATE-MD (C pkg)	Optional	Option diagnosis 1148#7=1
5	0i-MATE-MD (5 pkg)	Optional	Option diagnosis 1148#7=1, 1233#1=1
6	0i-MF	Yes

From the table above, you can determine whether your machine supports adding a 4th axis. (Some machines may already use the 4th axis for functions like a servo tool magazine—such cases are outside the scope of this discussion.)

Once the system requirements are met, we look at the motor and drive. Currently, the common types are the ai series and bi series. Motors from the ai and bi series are generally interchangeable and require little attention. However, drives must be selected carefully.

Our basic principle is to match the 4th axis drive to the same batch as the existing three axes. For example, if the first three axes use A06B-6114-HXXX, then the 4th axis should preferably also use A06B-6114-HXXX. Fanuc does offer some compatibility; for instance, the standard drive for the 0i-MD is A06B-6117-HXXX, but A06B-6240-HXXX can also be used. However, for the newer 0i-MF, only A06B-6240-HXXX is supported. So, as a general rule, stick with the same batch when possible.

Once the hardware is selected, we’ll talk about parameters and PLC. The Fanuc 0i series parameters are largely consistent with only minor differences. Refer to the table below for guidance:

No.	Parameter	Description	Remarks
1	1100 = 4	System controls 4 feed axes	0i-MC exclusive
2	1130 = 4	System controls 4 feed axes	0i-MC and 0i-MD
3	987 = 4	System controls 4 feed axes	0i-MF exclusive
4	1902#1 = 0	FSSB auto matching
5	1005#1 = 1	Zero return without stopper (for absolute motors)
6	1006#0 = 1	4th axis is a rotary axis
7	1008#0,#2 = 1	Rotary axis cycle function
8	1020	4th axis program name	Depends on axis location
9	1022	Axis in the basic coordinate system
10	1023	Servo axis number	Usually 4
11	1260	Movement per rotation	Usually 360
12	1320	Positive software limit	999999
13	1321	Negative software limit	-999999
14	1420	Rapid traverse speed	4000
15	1421	Rapid override F0 speed	100
16	1423	JOG feed speed	4000
17	1424	Manual rapid speed	4000
18	1428	Return reference speed	4000
19	1430	Max cutting feed speed	4000
20	1620	Rapid accel/decel time constant	100
21	1622	Cutting feed accel/decel time constant	322
22	1624	JOG feed accel/decel time constant	100
23	1815#4,#5=1	Absolute position setting	Set APC first, then APZ
24	2000	Initialization	Servo screen quick setting
25	2020	Motor code	Servo screen quick setting
26	2001	AMR	Servo screen quick setting
27	1820	Command multiplier	Servo screen quick setting
28	2084	Flexible gear numerator	Servo screen quick setting
29	2085	Flexible gear denominator	Servo screen quick setting
30	2022	Motor direction	Servo screen quick setting
31	2023	Speed pulse	Servo screen quick setting
32	2024	Position pulse	Servo screen quick setting
33	1821	Reference counter capacity	Servo screen quick setting
34	1825	Position loop gain	3000
35	1826	In-position width	10
36	1828	Position deviation limit during motion	10000
37	1829	Position deviation limit when stopped	500

Finally, regarding the PLC — since all CNC machine PLC programs on the market are custom-designed by their manufacturers, there is no unified standard. We can only provide a general overview.

As we are retrofitting a finished CNC machine, many signals don’t need to be handled manually. Just pay attention to the following internal PLC signals:

No.	Signal Content
1	G18.2 – 4th axis handwheel selection
2	G100.3 – 4th axis positive direction
3	G102.3 – 4th axis negative direction
4	G126.3 – 4th axis servo off
5	G130.3 – 4th axis interlock signal
6	F102.3 – 4th axis in-motion signal

In addition, you will need to handle:

4th axis unclamp detection signal
4th axis clamp detection signal
4th axis solenoid valve control signal

These three signals are not standardized and must be configured based on the actual situation by the installer.

Given the wide variety of CNC machines on the market and the differing design philosophies across manufacturers, installation personnel must continually summarize and accumulate experience to handle different scenarios effectively.