The G88 command is a part of the Computer Numerical Control (CNC) programming language used for boring operations where manual control is desired after the boring cycle. This command allows the machine to perform the boring operation and then stop, giving the operator the chance to manually retract the tool. This is particularly useful in situations where automated retraction could damage the workpiece or the tool.

Usage Format

The basic syntax for the G88 command is as follows:

G88 X_ Y_ Z_ R_ P_ F_;

Where:

• X and Y are the final hole position coordinates.
• Z is the final depth of the bore.
• R is the position above the hole where the boring cycle begins.
• P specifies the dwell time at the bottom of the hole.
• F is the feed rate.

Explanation

The G88 cycle works in several steps:

1. The tool moves to the R position above the hole.
2. It then proceeds to bore down to the Z depth at the specified F feed rate.
3. Once at the depth, the tool dwells for the P seconds.
4. The spindle stops turning.
5. The program pauses to allow the operator to manually retract the spindle.

This manual intervention provides a layer of control and safety, ensuring that the delicate parts of the operation can be handled with the operator’s expertise.

Example

Here’s a text diagram to illustrate the G88 cycle:

(R Position)
    |
    | (Feed rate F)
    V
   (Start of Bore)
    |
    | (Boring down to Z depth)
    V
   (Z Depth - Bottom of Bore)
    |
    | (Dwell for P seconds)
    |
   (Spindle Stops, Manual Retract)

And a sample code snippet using the G88 command:

N10 G00 X50 Y25 (Rapid move to starting position)
N20 G01 Z-5.0 R2.0 F100 (Move to R position above the hole)
N30 G88 X50 Y25 Z-25 R2.0 P5 F150 (Boring cycle with manual retract)

In this example, the tool rapidly moves to the starting position at X50 Y25, then moves to the R position 2.0 units above the hole. The boring cycle begins, moving to a depth of Z-25 at a feed rate of 150, with a 5-second dwell at the bottom. After the cycle, the spindle stops, and the program pauses for manual retraction.