G71 Roughing Cycle in CNC Programming Explained

The G71 roughing cycle in CNC programming is a canned cycle used to remove large amounts of material from a workpiece in a series of rough cuts. It automates the process of rough turning by repeatedly following a defined profile until the final shape is reached.

How It Works

The G71 roughing cycle works like a smart helper that takes a rough shape and gradually carves it down to the desired profile. Imagine sculpting a block of wood by making several passes with a chisel, each time removing some material but leaving a little extra for finishing. The CNC machine uses the G71 command to repeat this process automatically.

It reads a series of points that define the shape you want, then makes multiple passes along that path, cutting deeper each time until the roughing is complete. This saves time and effort compared to manually programming each cut, and it ensures consistent material removal.

Example

This example shows a simple G71 roughing cycle to machine a profile defined by points in a subprogram.

cnc

N100 G71 (Start roughing cycle)
N110 G71 U2.0 R1.0 (Depth of cut 2mm, retract 1mm)
N120 G71 P200 Q210 U0.5 W0.2 F0.25 (Subprogram from N200 to N210, finishing allowance)
N130 G70 P200 Q210 (Finishing cycle)
N140 M30

N200 L X50 Z0
N210 L X20 Z-40
N220 L X0 Z-60
N230 M99

Output

The machine will perform rough cuts along the profile defined between N200 and N210, removing 2mm depth per pass with 1mm retract, then finish the profile with G70.

When to Use

Use the G71 roughing cycle when you need to remove large amounts of material quickly from a cylindrical workpiece. It is ideal for turning operations where the final shape is complex and requires multiple passes to avoid tool overload.

For example, when machining engine parts, shafts, or any part with a stepped or curved profile, G71 helps automate rough cutting before finishing passes. This reduces programming time and improves machining efficiency.

Key Points

• G71 is a rough turning canned cycle for removing bulk material.
• It uses a subprogram to define the profile to machine.
• Multiple passes are made with specified depth and retract values.
• Usually followed by a finishing cycle like G70.
• Saves time and ensures consistent roughing cuts.

Key Takeaways

G71 automates rough turning by making repeated passes along a defined profile.

It removes large amounts of material efficiently before finishing.

The profile is defined in a subprogram with coordinate points.

Depth of cut and retract values control the roughing passes.

G71 is commonly paired with G70 for finishing the part.