CNC Lathe G33 Threading Program Example (Single-Pass Threading)
The following CNC lathe program demonstrates a simple external threading operation using the G33 threading cycle. In this example, the CNC lathe cuts an M20 × 2.0 metric thread over a 30 mm length in a single threading pass.
This program is intentionally kept very simple and uses a single threading pass without multiple cutting passes, making it easy for beginners to understand how G33 works and how the threading tool moves along the workpiece.
The workpiece is prepared with an Ø22 mm external diameter, and the thread is cut to approximately Ø20 mm major diameter with a 2.0 mm pitch over a 30 mm thread length.
O0001 (G33 SIMPLE THREADING)
G21 G99
T0101
G97 S500 M03
M08
G00 X22.0 Z2.0
G00 X19.6
G33 Z-30.0 K2.0
G00 X22.0
G00 Z2.0
M09
M05
M30G21 – Metric programming
G99 – Feed per revolution
G97 S500 – Spindle speed 500 RPM
G00 X22.0 Z2.0 – Position in front of the workpiece
G00 X19.6 – Move to the approximate thread minor diameter
G33 Z-30.0 K2.0 – Cut the thread
Z-30.0 = 30 mm thread length
K2.0 = 2.0 mm thread pitch
G00 X22.0 – Retract the tool
G00 Z2.0 – Return to the starting area
Single-Pass Threading vs Multiple-Pass Threading
This example uses only one threading pass:
G33 Z-30.0 K2.0This keeps the program short and makes the basic G33 operation easy to understand.
Cutting a complete thread to the final depth in one pass can be quite difficult and create cutting stress. In typical production machining, the threading tool typically removes material in several passes.
A typical multi-pass process would gradually reduce the X position:
Pass 1 → Light cut
Pass 2 → Deeper cut
Pass 3 → Deeper cut
Pass 4 → Deeper cut
Pass 5 → Finishing cutThe exact number and depth of passes depends on the material, thread size, insert geometry, machine rigidity, and spindle speed.
Threading can be easily cut using the G33 CNC command. In the example above, the tool is set to the desired cutting diameter and then a 30 mm long, 2.0 mm pitch external thread is produced using G33 Z-30.0 K2.0.
This example is of single-pass threading, so it is particularly useful for understanding the basic concept of G33. For actual production work, however, it is preferable to produce a better quality thread using multiple threading passes.
