Detailed usage of CNC lathe threading instructions G32, G92, G76

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CNC controlled lathes are capable of machining straight threads, tapered threads, and threads on end faces, as can be seen in the illustrations given. At the level of the way and method of machining, it is divided into a single-stroke thread cutting method, a simpler thread cutting cycle and a combined thread cutting cycle.

(1) Single-stroke thread cutting G32

Instruction format: G32 X(U)____Z(W)

The X(U) and Z(W) in the command are the endpoint coordinates of the thread, and F is the thread lead. The parameters to be determined before applying the G32 command are as shown in Fig. a. The meaning of each parameter is as follows:

In the case of tapered threads, the thread lead is L. In the X and Z directions, the one with the larger thread lead is selected.

α: Taper angle of the taper thread, if α is zero, it is a straight thread;

δ1 and δ2, which are the cut-in and cut-out amounts, are generally taken in the range of 2 to 5 mm, while δ2 is equal to (1/4 to 1/2) times δ1.

Figure a

Figure b

There is an example of thread machining, presented in Fig. b, which shows that the pitch of the thread is L equal to 3.5 mm, and the height of the thread is actually 2 mm, which involves a spindle speed of N of 514 rpm, a value of δ1 of 2 mm, and a value of δ2 of l mm, and it is to be turned twice, with a depth of l mm each time, and the machining programme is as follows:

N0 G50 X50.0 Z70.0 Setting the workpiece origin at the left end face

Designate N2, designate S514, designate T0202, designate M08, designate M03, and the spindle speed is 514r/min. Here, the thread turning tool is to be adjusted.

N4, G00, the X-axis moves to the 12.0 position and the Z-axis moves to the 72.0 position, thus going quickly to the point where thread turning is said to begin, the point with the coordinates (12.0, 72.0).

N6 G32 X41.0 Z29.0 F3.5; thread turning

N8 G00 X50.0; rapid return along the X axis

N10 Z72.0; rapid return along the Z axis

N12 X10.0; fast walk to start of second thread turning

N14 G32 X39.0 Z29.0; second thread turning

N16 G00 X50.0; rapid return along the X axis

N18 G30 U0 W0 M09; back to reference point

N20 M30; end of programme

(2)Thread cutting cycle instruction G92

G92 is a thread cutting cycle, which belongs to the simple thread cycle, it can cut taper threads and cylindrical threads, it is basically the same cycle route compared with the single-shape fixed cycle mentioned before, only that the subsequent feed amount of F has become the pitch value. Its instruction format is:

G92 X(U) ____Z(W);

As shown in the figure, it is the graph of thread cutting cycle, the tool starts from the starting point A, and then follows the path from A to B, then to C, then to D, and finally back to A. The dotted line in the figure shows that the tool moves rapidly, and the solid line means that the tool moves according to the working speed specified by F. X and Z are the values of coordinates of the end point of the thread, that is, the point C, and U and W are the incremental value of the starting point to the end point, and R is the difference between the radius of the end point of the taper thread and the radius of the starting point, and the positive and negative values of R are judged in the same way as G90. U and W are the incremental values from the starting point to the end point, R is the difference between the radius of the end point and the radius of the starting point of the taper thread, the judgement of the positive and negative values of R is the same as that of the G90, the cylindrical thread can be omitted when R is equal to 0, F is the pitch value, and the angle of the thread cutting back is 45°.

Example of thread machining: Machining a thread as shown in figure b above. The procedure is:

N0 G50 X50.0 Z70.0; set the workpiece origin at the left end face

For N2, specify S514, T0202, M08, M03, where S stands for a spindle speed of 514 r/min, and T calls out the thread turning tool.

Place N4, G00 and X is 12.0, Z is 72.0, and go quickly to the start point of thread turning, which has coordinates (12.0, 72.0).

N6, G92, X41.0, Z29.0, R29.0, F3.5 for thread turning.

N8 X39

N10 G30 U20 W20 M09; back to reference point

N12 M30; end of programme

(3) Thread cutting multiple cycle instruction G76

The G76 thread cutting multi-cycle instruction is more concise than the G32 and G92 instructions, in which only one relevant parameter needs to be specified in the programme, and then the thread machining process will be carried out automatically. The execution process of the instruction is shown in the figure below, and the format of the instruction is as follows:

The G76 thread cutting instruction, the format of which, requires two instructions, to be defined, looks like this:

G76 P(m)(r)(a);

The significance of the relevant geometric parameters in Eq. is shown in the figure, and the definition of each parameter is as follows:

m: number of fine turning repetitions from 1-99, this parameter is a modal quantity.

r, that is, the value of the thread end chamfer, its value can be set in the range from 0.0L to 9.9L, the coefficient should be 0.1 as a multiple of the integer, need to be in the 00 to 99 between the two integers to be expressed, where L refers to the pitch, this parameter belongs to the modal quantity.

a: The tool angle, which can be selected from the six angles 80°, 60°, 55°, 30°, 29° and 0°, is expressed as a two-digit integer and is a modal quantity.

Use address P to specify m, r, and a together; for example, m equals 2, r is 1.2L, a is 60°, and the presentation is.

Q: The minimum turning depth, which is specified by programming the radius, is (Δd - Δd ) for each turn in the turning process and is locked in if the calculated depth is less than this limit value. This parameter is a modal quantity.

R: Finishing margin, specified by radius programming. This parameter is a modal quantity that

X(U), Z(W): Thread endpoint coordinates

i: Thread taper value, specified by radius programming. If R=0 it is a straight thread.

k: Thread height, specified by radius programming.

Δd: First turning depth, specified by radius programming.

L: Pitch.

In the above two instructions, the values after the Q, R, and P addresses are expressed without a decimal point.

A set of examples of Group of Seven related thread turning is presented, which shows a section of direct threading on a component shaft, the thread has a height of three point six eight millimetres, the pitch is six millimetres, the chamfer at the end of the thread is one point one L, the angle formed by the tip of the tool is sixty degrees, the depth of the first turning is one point eight millimetres, and the minimum depth of the turning is zero point one millimetre. The procedure is as follows:

n16 g76 q100 r200;

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