The G71 rough turning cycle is a powerful G-code function used in CNC programming for lathes. It allows for efficient and precise material removal during the roughing phase of turning operations. This cycle automates the process of cutting a component to its rough dimensions before the finishing passes.

Usage Format

The G71 cycle is typically written in two lines:

G71 U(depth of cut) R(retract amount);
G71 P(start of profile) Q(end of profile) U(finish allowance in X) W(finish allowance in Z) F(feed rate);

Explanation

• U specifies the depth of each roughing pass.
• R defines the retract distance away from the part between passes.
• P and Q denote the start and end line numbers of the shape subroutine.
• F sets the feed rate for cutting.

The cycle follows a defined profile, which is programmed as a separate subroutine within the G-code.

Example

Here’s a simple text diagram and example code for a G71 rough turning cycle:

% Text Diagram:
%
%        _________
%       /         \
%      /           \
%     /             \
%    /               \
%   /                 \
%  /___________________\
%
% G-code:
O0001 (Program number)
T0101 (Tool selection and offset)
G97 S500 M03 (Spindle speed and direction)
G00 X100 Z5 (Rapid move to start position)
G71 U2.5 R0.5 (Roughing cycle parameters)
G71 P100 Q200 U0.1 W0.1 F0.2 (Roughing cycle definition)
N100 G00 X90 Z2 (Start of profile subroutine)
N110 G01 Z-50 F0.2 (Linear move to Z-50)
N120 X80 Z-60 (45-degree chamfer)
N130 X70 (Straight line to X70)
N140 G02 X60 Z-65 R5 (Radius to X60)
N150 G01 Z-100 (Linear move to Z-100)
N160 G00 X150 Z200 (Rapid move away from part)
N200 M30 (End of program)

This example demonstrates the use of the G71 cycle to rough turn a profile with a chamfer and a radius. The cycle parameters dictate the depth of cut, retract distance, and finishing allowances, while the subroutine (N100 to N150) outlines the profile to be machined.