G76 Threading Cycle Explanation

G76 is a canned cycle that simplifies single point threading. It generates multiple passes to gradually cut a thread to its full depth.

G76  P010060  Q0015  R0.001

G76.1  X0.2075  Z-0.500  P0212  Q0090  F0.0357  R0.0

G76 consists of 2 lines of code that fully define the desired thread, these lines are called out by the G76 and G76.1 G-codes.

Note: The cutting tool should be positioned where the threading passes will start before the G76 sequence is initiated.

Line 1 (G76):  The “P” specifier controls 3 parameters. The first 2 numbers following the P specify the number of dead passes. The middle 2 numbers specify the pullout angle in degrees. The last 2 numbers specify the angle of the thread. Each of these parameters must be expressed using a 2-digit number.

The “Q” specifier controls the minimum depth of cut on any intermediate pass. This value must be entered as a 4 digit number and is received by the control as the 4 digits the follow the decimal place (0.xxxx).

The “R” specifier controls the depth of cut on the final cutting pass. This number can be smaller than the programmed “Q” minimum depth of cut pass.

Line 2: The “X” specifier controls the minor diameter of the thread. The “Z” specifier controls the end coordinate of the thread in the Z direction.

The “P” specifier controls the radial depth of thread - half the diameter difference between the major and minor diameter. This value must be entered as a 4 digit number and is received by the control as the 4 digits that follow the decimal place (0.xxxx).

The “Q” specifier controls the depth of the first threading pass. This value must be entered as a 4 digit number and is received by the control as the 4 digits the follow the decimal place (0.xxxx).

The “F” specifier controls the pitch of the thread.

The “R” specifier controls the taper adjustment of the thread. This value is entered in inches diametrically that thread size will increase over the thread length. When creating a tapered thread the “X” specifier that controls the minor diameter will likely need to be adjusted to gauge properly.

The code in the data block above creates a ¼-28 thread 0.500” deep with a first pass of 0.009”, last pass of 0.001”, with no intermediate pass smaller than 0.0015”, one dead pass, no pullout angle, and no taper.