The G85 command is used in CNC programming to perform precision boring operations. This cycle is similar to the G81 drilling cycle but with the added capability of a controlled feed rate during retraction, which can help prevent tool damage and ensure a high-quality finish.

Usage Format

The standard format for the G85 command is as follows:

G85 X_ Y_ Z_ R_ F_

Where:

• X and Y are the final hole position coordinates.
• Z is the final depth of the boring operation.
• R is the position of the retract plane.
• F is the feed rate for both boring and retraction movements.

Explanation

During a G85 cycle, the tool moves rapidly to the R plane, then feeds down to the Z depth at the specified feed rate. Once the depth is reached, the tool retracts at the same controlled feed rate back to the R plane. This differs from other cycles where the retraction is typically done at rapid speed.

Example

Here’s a simple example of a G85 cycle in a CNC program:

N10 G90 G20 (Set absolute mode and inch units)
N20 G00 X1 Y1 (Rapid move to hole position)
N30 G43 Z0.1 H01 (Tool length compensation)
N40 G85 X1 Y1 Z-1 R0.1 F5 (Boring cycle)

In this example, the tool will move to coordinates X1, Y1, bore down to Z-1 inch at a feed rate of 5 inches per minute, and then retract back to Z0.1 inch at the same feed rate.