G89 – Boring, Dwell & Feedrate Retract

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The G89 g-code command is a versatile instruction used in CNC programming for boring operations. It allows the machine to bore a hole, pause at the bottom of the hole for a specified dwell time, and then retract at a controlled feedrate. This process ensures precision and control when machining parts that require exact hole dimensions and finishes.

Usage Format

The standard format for the G89 command is as follows:

G89 X... Y... Z... R... P... F...

Where:

  • X and Y denote the target coordinates for the hole’s center.
  • Z represents the depth of the hole.
  • R is the position above the hole where retracting starts.
  • P specifies the dwell time at the bottom of the hole.
  • F is the feedrate for retracting from the hole.

Explanation

When the G89 command is executed, the CNC machine moves the boring tool to the specified X and Y coordinates. It then bores down to the Z depth at the current feedrate. Upon reaching the depth, the tool dwells for the P amount of time, allowing for any necessary adjustments or stabilization. Finally, the tool retracts to the R position at the F feedrate, ensuring a smooth finish and precise control of the tool’s exit from the material.

Example

Here’s a text diagram and a sample code snippet to illustrate the G89 command in action:

(Start)
|
|   (Dwell P)
|   v
|   Z-depth
|   .
|   .
|   .
|---X/Y Target---> (Rapid move to X and Y)
|
(Retract at F feedrate)

Sample Code:

G00 X50 Y25 (Rapid move to start position)
G43 Z5 H01 (Tool length compensation)
G89 Z-15 R2 P500 F100 (Boring operation with dwell)

In this example, the tool rapidly moves to the coordinates X50 and Y25. It then compensates for tool length before performing a boring operation to a depth of Z-15. The tool dwells at the bottom for 500 milliseconds before retracting to the R2 position at a feedrate of 100.

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