Here is a question:
When threading using the G76 cycle:
The thread height is 1.8 mm, and the finishing allowance is 0.06 mm.
You want to split the roughing process into 9 passes.
What value should be entered for Q in the second line?
Answer: Q580
Calculation method:
Depth of the first pass
= Total roughing depth ÷ √Number of roughing passes
First, calculate the total roughing depth:
1.8 – 0.06
= 1.74 mm
Then, calculate the depth of the first pass:
1.74 ÷ √9
= 1.74 ÷ 3
= 0.58 mm
So, write this in the second line:
Q580
(Note: The Q value does not include a decimal point.)
This formula can also be used to reverse-engineer someone else's program.
If the second line reads:
Q500
The depth of the first pass is:
0.5 mm
To estimate the number of roughing passes:
N = (1.74 ÷ 0.5)²
= 12.11
Assuming the minimum cutting depth parameter in the first line does not intervene, a 13th pass would be required to reach the total roughing depth.
Remember these two formulas:
If the number of passes is known, calculate Q:
d₁ = h′ ÷ √N
If Q is known, estimate the number of passes:
N = (h′ ÷ d₁)²
Where:
d₁: Depth of the first pass
h′: Total roughing depth
N: Number of roughing passes
One final reminder:
The actual number of passes may also be influenced by the minimum cutting depth setting (in the first line), the number of finishing passes, and system parameters.
Use this formula to:
Determine the Q value or analyze a program.
First, check the thread height, finishing allowance, and planned number of passes, then calculate your own values.
