How To Cut Trapezoidal Thread?

The Methods Of Cut Trapezoidal Thread

Trapezoidal thread is a widely used transmission thread, which is mainly processed by CNC machine tools. Because of the higher accuracy requirements for trapezoidal threads, the machining process will be more difficult due to accuracy and other reasons. The main problems will be boring or piercing. If the tool is damaged, the machine will be damaged. But as long as the machining technology analysis is reasonable, effective machining methods are used, and proper programming instructions are used, qualified trapezoidal threads can be made.

It’s important to start. If you want to make a good trapezoidal thread, you need to know how to calculate the trapezoidal thread.

Tooth angle: 30 ° stipulated in China’s standard, pitch: regulated by thread standard.

Crest width: f = 0.366P.

Alveolar bottom width: w = 0.366P-0.536αc

External trapezoidal thread: large diameter (nominal diameter) d; middle diameter d2 = d-0.5P; small diameter d3 = d-2h3; tooth height: h3 = 0.5P + αc

Code of trapezoidal thread: The code of trapezoidal thread is represented by the letter “Tr” and the nominal diameter × pitch, the unit is mm. The left-hand thread needs to be marked with “LH” after the size specification, and the right-hand thread does not need to be marked.

Come directly to the important-CNC car G76 dry trapezoidal thread.

Programming format with G76 instruction

G76 P (m) (r) (α) Q (△ dmin) R (d)

G76 X (U) Z (W) R (i) P (k) Q (△ d) F (L)

m: thread finishing times 00 ～ 99 (unit: times).

r: chamfering amount of thread tail, the value can be set between 00 and 99 (unit: 0.1 × L, L is lead).

α: Angle of blade tip. You can choose one of 80 °, 60 °, 55 °, 30 °, 29 ° and 0 °.

△ dmin: The minimum back-feeding amount (radius value) when the thread is rough turning, unit: μm. When the amount of back-feeding during cycle operation is less than this value, the amount of back-feeding is locked at this value.

d: Machining allowance (radius value) of thread finishing, unit: mm.

X, Z: Coordinate of thread cutting end point.

U, W: Incremental coordinate value of thread end point relative to cycle start point.

i: Thread radius difference (starting point of thread cutting relative to end point of thread cutting), unit: mm.

k: thread height (radius value), unit: μm. Calculate by k = 0.6495P.

△ d: the amount of knife eaten by the first thread back, unit: μm.

L: thread lead, unit: mm.

Live to learn, use nonstop, take Tr36X6 as an example to actually use G76

Tooth height h3 = 0.5P ＋ αc = 3.5

Large diameter d = 36;

Small diameter d = d-2h3 = 36-2 × 3.5 = 29

Turning trapezoidal thread

(1) Write a program to set the minimum back-feeding amount of rough turning trapezoidal thread to 0.05mm, and the remaining amount of finishing turning to 0.06mm

Write a trapezoidal thread NC program.

O0001;

T0303 (trapezoid knife);

M03 S400;

G43 G99 G40;

G00 X38 Z5;

G76 P020530 Q50 R0.06; (Set the finishing twice, the chamfering amount is equal to 0.5 times the pitch, the profile angle is 30 °, the minimum back-feeding amount when the thread is rough turning is 0.05mm, and the finishing turning margin is 0.06 mm.)

G76 X29 Z-38 P3500 Q600 F6; (The thread height is set to 3.5mm, the first knife cutting depth is 0.6mm.)

G00 X100;

Z100;

M05;

M30;

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Link to this article：How To Cut Trapezoidal Thread?

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