CNC Lathe | G85 Cycle | Front Boring

In this article, we describe how to use G85 cycle for front boring in CNC lathe (turning) machines with all details and examples.


G85 Cycle Introduction

G85 cycle is used in CNC turning machines for boring holes from the front to the workpiece. It is the same as the G89 cycle as a command format, the only difference is that it is used for boring holes in the Z axis direction, not in the X axis direction.

After the command is used, boring to the other coordinates is continued by positioning the X axis or C axis. The G85 cycle continues to run until the G80 command arrives.

G85 Cycle Format

G85 Z(W)_ R_ P_ F_ K_ M_ ;


Z_ or W_ : Final drilling depth (Z for absolute, W for incremental)
R_ : The distance from the initial level to point R level
P_ : Dwell time at the bottom of a hole
F_ : Cutting feedrate
K_ : Number of repeats (When it is needed.)
M_ : M code for C-axis clamp (when it is needed.)

After positioning, rapid traverse is performed to point R. Drilling is performed from point R to point Z. After the tool reaches point Z, it returns to point R at a feedrate twice the cutting feedrate.

You may be interested also:
“CNC Lathe | G84 Cycle | Front Tapping”

G85 Cycle Examples

G85 CNC Program Example – 1

O1234; Program number
M51 ; Setting C-axis index mode ON
M3 S2000 ; Rotating the drill
G00 X50.0 C0.0 ; Positioning the drill along the X- and C-axes
G85 Z-40.0 R-5.0 P500 F5.0 M31 ; Drilling hole 1
C90.0 M31 ; Drilling hole 2
C180.0 M31 ; Drilling hole 3
C270.0 M31 ; Drilling hole 4
G80 M05 ; Canceling the drilling cycle and stopping drill rotation
M50 ; Setting C-axis index mode off
M30; Program end
M31 : C axis Clamp

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