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G76 for internal threading?


Jul 10, 2016
I have a 96 Hwacheon with Fanuc OT and mostly use a USB in tape mode but wanted to accomplish some internal threading using the G76 command. For internal threading is it simply change X(u) to the negative -Diameter?

FORMAT G76 P(m) (r) (a) Q(∆dmin) R(d)
G76 X(u) Z(w) R(i) P(k) Q(∆d) F(f)

ex) P 0 2 1 0 6 0 Repeating time, Chanfering volume 1.0 lead, Angle of thread face

P(m) : Repeating time before the final thread
(r) : Chamfering at the end part of thread
(a) : Angle between threads
Q( §Edmin) : Min. cut volume(Example : Calculate as Q100=NC and process at least more
than 0.1 for processing of one time)-0.1(Decimal point is vot allowed)
R( §Ed) : Finishing clearance(Final finishing clearance)
X(u) : Core diameter of thread
(Command the value of Outer diameter of thread-<height of threadx2>)
Z(w) : Z spindle coordinate at the end point of thread process
R(i) : For omitting, straight thread and R– : X+ and Taper thread
R+ : X– and Taper thread
P(k) : Height of thread(Omit the decimal point <Example>P900=0.9mm)
Q(d) : Initial cut volume (Omit the decimal point <Example>Q500=Designate) the radius
F(f) : Cutting feedrate(Lead)


Sep 10, 2010
Victoria Australia
For internal threading is it simply change X(u) to the negative -Diameter?

I can only see one question in your Post, that being the sign of the X coordinate in the second G76 Block. If your cutting tools (OD/ID Turning) operate on the + side of the machine's centre line, then the sign of the X value for an Internal Thread will be +. With an OD Thread, the X coordinate specifies the Minor Diameter of the Thread, whilst with an Internal Thread, the Major Diameter is specified by the X Coordinate.

The control determines whether an Internal or External Thread is being cut by comparing the X Start Coordinate of the Threading Tool and the X coordinate specified in the G76 Block.

You can still Drip Feed (Tape Mode) with a G76 Threading Cycle in the program.




Jun 7, 2021
I could be wrong but I thought the r value would be left zero on straight threads, and whatever value you need for tapered threads(like npt). I would think the taper at the first of threads would come from the turning profile.