CNC Milling | G85 Cycle | Boring (Ream Holes)

G85 Cycle Introduction

G85 cycle is used in CNC Machining Centers (CNC Milling machines) to boring and ream holes. The most important difference of this cycle is that the reamer tool goes up again with the F cutting feedrate that it enters into the hole because it will spoil the surface in case of rapid removal. In other words, as in other cycles, after the hole boring process is finished, it comes out from the bottom of the hole not with fast movement, but with the F feedrate that it given in cycle.

With this cycle, the reamer tool goes to the coordinate specified in the program, quickly approaches the height of Z specified by R, ream the holes depth given by Z .. with the feedrate indicated by F and goes back to the distance R with again F feedrate movement. If another coordinate is given afterwards, it moves there and the cycle continues until G80 is commanded.

G85 Cycle Format

G85 X… Y… Z… R… P… K… F…


G85 : Boring Cycle ( Usually for ream holes )
X : Hole position in X axis
Y : Hole position in Y axis
Z : Z axis end position = Z depth = Hole depth
R : Z axis start position = R level = Clearance
P : Dwell time at the bottom of hole
K : Number of cycle repetitions
F : Feedrate

Things to Know

  • X and Y coordinates where the hole will be boring are not usually given in the same line. Instead, the machine is sent to the first hole coordinate in the program, and then boring with the G85 cycle is started.
  • In general, the cycle is not repeated with K.
  • What is written in the first two items describes the methods generally used by the users in the market. The command format has been written technically appropriate, the command I want you to know can be written and applied as described here, although the first two items are frequently encountered in the market due to the ease of control of the program and the ease of writing.
  • The G85 cycle is usually used with the G98 command. You can find details about the G98 and G99 command on our website.
  • G85 cycle is used in CNC Machining Centers (CNC Milling machines) to boring and ream holes.
  • After using the G85 cycle, the cycle must be canceled with the G80 command. If it is not canceled with G80, your machine will boring holes with the conditions specified in the G85 line in every different coordinate included in the program.
  • If the command is used with G98, it will use the Z height that it uses to “boring the first hole” when moving between the coordinates to be boring.
  • If the command is used with G99, it will use the R height “when moving between the coordinates to be boring”.
  • If the program is stopped during G85 cycle and some manual movements are made, it must be moved to the point where the program is stopped manually before starting the program again.
  • The G85 command is not work under MDI mode. Although it is technically related to machine type, control unit type and parameters, not running cycles under MDI mode is more suitable for work safety and correct machining of the workpiece.
  • M98 and M99 commands are not used in lines where G85 command is written.

G85 Cycle Examples

G85 CNC Program Example – 1

G85 Cycle Program Example

T05 M06;
S600 M03;
G90 G00 G54 G43 H5 Z50;
X29 Y23;
G98 G85 Z-22 R10 F120;
G00 Z100;