CNC lathe threading instructions G32, G92, G76 examples of explanation


Today, we analyze and analyze the three threading instructions G32, G92 and G76 in detail!

I. Threading preparation knowledge

1. Threading feed method:

Straight into the method: small pitch

2. Depth of cut type:

Constant type:

Decreasing type:

3. Speed up feed section δ2 and speed down exit section δ1 :

(Empty cutter introduction amount δ2 and empty cutter export amount δ1)

(Cutting distance δ2 and cutting distance δ1)

The speed up feed section δ1 and the speed down retract section δ2 are shown in the figure below:

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4. Calculation of each main dimension of triangular thread:

Empirical formula: d = d male - 0.1P

                 d:Actual major diameter

                 d1 = d male - 1.3×P

                 d1: small diameter of the thread

                 h = ( d - d1 )/2

                 h:Thread height

Theoretical formula: d1 = d male -1.0825×P

                 h = 0.6495

II. Equal pitch straight thread:

Instruction: G32;

Function: G32 instruction can cut and process cylindrical threads, conical threads and face threads of equal pitch;

Format: G32 X(U)____Z(W)____F____;

Explanation: ①X____Z____: coordinates of thread end point in absolute value programming;

          ② U____W____: coordinates of thread end point in incremental value programming;

          ③F____: thread lead or pitch;

Precautions about turning threads

1、Thread processing needs to be adapted to the spindle speed, too high a system response will not be able to keep up with the phenomenon of messy buckle threads, the experience of the spindle speed n <= 1200 / P-80

2、1 inch=25.4mm

3、The pitch of the imperial thread is expressed by the number of teeth per inch, such as 19/in---19 teeth per inch. Pitch = 1in/number of teeth = 25.4/number of teeth

4、When machining threads, the appropriate lead-in and lead-out lengths should be retained

5、When processing multi-head threads, F indicates the lead, and the pitch when processing single-head threads.

6、When machining multi-head threads, the tool should be moved one pitch to the left or right with G00 or G01 after machining one head, and then programmed according to the requirements.

When turning threads, the spindle speed should not be changed, otherwise it will affect the accuracy (sealing) of the threads.

8、Thread depth of one side h=0.6495Xpitch.

9. When cutting triangular threads at high speed, the extrusion of the turning tool will make the size of the outer thread diameter larger, so the diameter of the outer circle before turning should be smaller than the thread diameter.

10. When turning internal threads, the diameter of the inner hole will become smaller due to the extrusion of the turning tool, so the diameter of the hole before turning the internal threads should be larger than the basic size of the small diameter of the internal threads.

11、Low speed turning threads have high precision and small surface roughness value, but low efficiency.

④ When machining tapered thread, the thread lead is specified by the value in the Z-axis direction when its inclination angle α﹤45°; when the inclination angle 45°﹤α﹤90°, the thread lead is specified by the value in the X-axis direction, as shown in the following figure:

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Example 2.6.1: Machining the thread shown in the figure below:

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Third, thread cutting cycle:

Instruction: G92 (G82 for HNC-21T)

Function: G92 is a simple thread cycle instruction, which can simplify the program, and the instruction can cut and process cylindrical threads and conical threads;

Format：G92 X(U)___Z(W)___R___F___;

Description：1）X____Z____:the coordinates of the end point of thread in absolute value programming;

2）U____W____:the coordinates of the thread end point for incremental value programming;

3）R____:radius difference between thread cutting start point and thread cutting end point, can be omitted if R is 0 when turning cylindrical thread;

(4) F____: thread lead (pitch in case of single head thread) (positioning mm).

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Thread Cutting Compound Cycle

Instruction: G76

Function: G76 can complete compound thread cutting cycle.

Format：G76 Pmra Q△min (unit μm) Rd (unit mm);.

G76 X(U)____Z(W)____Ri(unit μm) P unit k(μm) Q△d F____;

Example 2.6.2: As shown in Fig. 2-10, for a section of cylindrical thread on the part drawing, the tooth height is 3.68 mm, the pitch is 6 mm, the thread closing length is 0.1 P, the tool tip angle is 60 °, the first depth of cut is 1.8 mm, the minimum depth of cut is 0.1 mm, the finish margin is 0.2 mm, the number of finishing operations is 1, and the outer cylindrical surface is finish turned before the thread cutting.