Imagine how a CAM program might work for the lathe. You draw the profile that you want to turn on a part, push a button, and out comes g-code that converts that profile into the right moves to cut the profile in multiple passes based on the depth of cut for each pass you specified. G71 and its cousins are some of the most useful canned cycles you’ll ever come across for the lathe, because they essentially do what I’ve just described. The difference is that instead of specifying a profile in a CAD program, you specify the profile using g-codes.

Here is a very simple profile:

Simple G71 Profile

A simple profile consisting of 3 G01 segments with a G00 to the starting point…

This profile consists of 3 G01 line segments with a G00 rapid move to the starting point of the profile. The code associated with the profile is trivial:

N1 G0 X1.6
N2 G1 Z-4.0
N3 X2.5 Z-5.0
N4 G1 X4

Now here is a G71 command to rough turn that profile as simulated by our G-Wizard CNC Simulator and Editor:

G71 Simulation

The simulated G71 makes 2 roughing passes and then cuts the profile…

And here is the code that was simulated:

% Top to bottom, right to left
( One line G71 )
G0 X4 Z1.0 (Start Position before commanding the cycle)
G71 P1 Q4 D1.0 F2 U0.2 W0.1
N1 G0 X1.6
N2 G1 Z-4.0
N3 X2.5 Z-5.0
N4 G1 X4

There’s not much more needed than the profile to get the job done. G71 can save you a whole bunch of time and make it pretty easy to crank out some parts without needing to access a CAM program. Before we dive into exactly how to program a G71, we need to cover the different flavors of G71 you may run into.

If you’re interested in learning more about G71, check out our new tutorial on it. It’s part of our G-Code tutorial course.


Like what you read on CNCCookbook?

Join 100,000+ CNC'ers!  Get our latest blog posts delivered straight to your email inbox once a week for free. Plus, we’ll give you access to some great CNC reference materials including:

  • Our Big List of over 200 CNC Tips and Techniques
  • Our Free GCode Programming Basics Course
  • And more!

Just enter your name and email address below:

Full Name
Email *
100% Privacy: We will never Spam you!

Rate this post