The Haas G71 command is a powerful G-code used in CNC programming for lathes. It’s designed to simplify the process of roughing out material from a workpiece by automating repetitive cutting cycles.
Usage Format
The basic syntax for the G71 command is as follows:
G71 U (roughing depth) R (retraction distance);
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 retraction distance for the tool away from the workpiece.
- P and Q denote the start and end block numbers of the toolpath subroutine.
- W sets the finish allowance in the Z-axis, and F is the feed rate for the cycle.
Example
Consider a scenario where we need to rough out a cylindrical workpiece with a simple taper. Here’s how we might use the G71 command:
% (Program Start)
O1000 (Program Number)
T01 M06 (Tool Change to Tool 1)
G97 S500 M03 (Spindle Speed and Rotation)
G00 X100. Z5. M08 (Rapid Move to Start Position and Coolant On)
G71 U2. R1. (Roughing Cycle Depth and Retraction)
G71 P100 Q200 U0.5 W0.2 F0.15 (Roughing Cycle Parameters)
N100 G00 X90. (Start of Profile Subroutine)
G01 Z-50. (Linear Move to End of Part)
X80. Z-60. (Tapered Section)
N200 G00 X100. Z5. (End of Profile Subroutine)
G70 P100 Q200 (Finishing Cycle)
M30 (Program End)
%
In this example, the G71 line sets up the roughing cycle with a 2mm depth of cut and a 1mm retraction. The P and Q values reference the start and end of the profile subroutine, which is defined by N100 and N200. The U and W values leave a 0.5mm and 0.2mm allowance for finishing in the X and Z axes, respectively.
Here’s a text diagram to illustrate the profile:
Front View of the Workpiece
|<--- 50mm --->|
______________
/ \
| |
\______________/
Side View of the Tapered Section
|<--- 10mm --->|
__
\
\
\__
The front view shows the overall length of the workpiece, while the side view details the tapered section created by the G71 roughing cycle.