Lecture 10 | Program for Multiple Turning Cycle | Roughing Cycle | G71 | CNC Machining Programming
The G71 roughing cycle enables us to remove material quickly on a CNC Lathe while also writing the cutter path as a subroutine that can be reused during the finishing cycle (G70).
The syntax for this is:-
G71 U R;
G71 P Q U W F;
Here,
U – Depth of cut in X axis
R – Relief (Retraction) amount
P – Starting block of the profile
Q – Finishing block of the profile
U – Finishing allowance in X axis
W – Finishing allowance in Z axis
F – Feed Rate
G71 is our G-Code that lets the controls know that we wish to use a roughing cycle and that the following information applies to that.
The U on the first line of code is the depth of cut of each roughing pass. The R refers to how far the tool will retract from the part in X when returning in rapid to the start of the cycle.
The 'P' and 'Q' values define the start and end point of our subroutine respectively. These values can be any 1,2,3 digit value as long as it matches the 'N' numbers of the subroutine. This is easier to explain with examples.
Suppose we are taking
N10;
SUBROUTINE OF PROFILE;
N20;
In the above example, 'P' would be P10 and 'Q' would be Q20 so they match the 'N' numbers.
The 'U' on the second G71 line tells the machine the amount we wish to leave on for a finishing pass in X while the 'W' is the finishing allowance in Z.
Finally 'F' is our feed rate in mm/min. or in mm/rev.
G70 finishing cycle, calling the subroutine:-
Because we used a subroutine during writing our roughing cycle, writing the finish pass is extremely simple
G70 P10 Q20;
It's as easy as that.
This single line of code tells the machine that we wish to use a finishing cycle (G70) and that the tool should follow the path of the subroutine that can be found between the N10 and N20 within our program.
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