CNC Lathe | G33 and G34 Thread Cutting

G33 and G34 Codes Introduction

The following preparatory functions are available for cutting threads.

G33: Thread cutting with constant lead / tapered threads / screw threads.
G34: Thread cutting with linear lead increase / decrease

The spindle speed is read from the position coder on the spindle in real time and converted to the cutting feedrate for FPM, which is used to more the tool.

Spindle speed must remain constant from rough cutting through finish cutting, else incorrect thread lead will occur.

G33 and G34 Codes Format

G33 Code Format

G33 IP_ F_ ;

Parameters

IP : End point
F : Lead of the long axis

The range for thread lead is 0.0001 mm to 500.000 mm

G34 Code Format

G34 IP_ F_ K_ ;

Parameters

IP : End Point
F : Lead in longitudinal axis direction at the start point
K : Increment / Decrement of lead per spindle revolution.

Range for K is 0.0001 to 500.000 mm/rev.

Things to Know

  1. Feedrate override is not effective (fixed at 100X) during thread cutting
  2. If FEEDHOLD push button is pressed during thread cutting, the tool will stop after a block not specifying thread cutting is executed, similar to single block.
  3. Spindle speed override is not effective in thread cutting mode.

Threads

Variable Lead

Threads with variable lead are cut with;

G34 (End point) (F) (K)

F : Lead in longitudinal axis direction at the start point
K : Increment / Decrement of lead per spindle revolution. Range for K is 0.0001 to 500.000 mm/rev.

Multiple Start

Multiple start threads are cut by shifting the start point of the thread for each start, by the distance equal to pitch (lead divided by number of starts).

If the lead is 4mm and number of starts are 2, and if the start point for the first start of the thread is selected as Z4, then the start point for the second start of the thread is selected as either Z2 or Z6.

G33 and G34 Codes Examples

G33 CNC Program Example - 1

CNC Lathe G33 Cycle Tapping Example

O5555 ;
T0000 ;
G0 X0.Z-100 ;
T0303 M07 ;
G97 S200 M04 ;
G0 X0. Z5. ;
G33 Z-20. F1.75 ;
/ G01 Z-20. F1.75 ;
S0 ;
S200 M03 ;
G33 Z5. F1.75 ;
/ G01 Z5. F1.75 ;
S0 T0000 M09 ;
G0 X0.2-100. ;
M05 ;
M30 ;