G98 and G99: How to Retract a Tool on a CNC Machine

There are two types ofgcodes used to make a tool retract on a CNC machine, G98 and G99. G98 is used for a single shot return, while G99 is used for a continuous return. The big difference is that with G98, the tool stays at the same Z position as it was when it first broke through the material. With G99, the tool moves up to the Z home position, which is set by the user.

G98 and G99 are two methods of retracting a tool on a CNC machine.

G98 and G99 are two commands used to retract a tool on a CNC machine. G98 tells the machine to retract the tool to the original position, while G99 tells the machine to retract the tool to the home position.

G98 is the standard method, and G99 is the alternative method.

ISO 9283:1992 Geometrical Product Specifications (GPS) – Inspection by means of axes – Concept and acceptance conditions covers the fundamental concepts for inspection by means of axes.

The main acceptance criterion for Inspections by means of axes is founded on the attainment of a specified value for the orientation of a feature or a datum. This value is known as the acceptance value.

In principle, two methods for the calculation of the acceptance value are possible: G98 is the standard method, and G99 is the alternative method.

The main difference between the two methods is that, in G98, the tolerance on the feature or datum is divided equally between angular (i.e. three-dimensional, or 3D) and linear (i.e. two-dimensional, or 2D) components, whereas in G99, the tolerance is applied only to the 3D component.

This has the consequence that, for a given tolerance, G98 will result in a larger number of rejections than G99.

G98 is the most commonly used method, as it leads to fewer false positives (i.e. parts that are incorrectly classified as non-conforming).

G98 retracts the tool to the original Z position, while G99 retracts the tool to the R position.

G98 and G99 are both used to retract the tool, but they have different purposes. G98 is used to retract the tool to the original Z position, while G99 is used to retract the tool to the R position. The R position is the position where the tool is safe to be retracted without damaging the workpiece or the tool.

G98 is the preferred method, as it is more precise.

G98 is the preferred method, as it is more precise.

This may be surprising to some, but G98 is actually the preferred method for many CNC machine operators. The reason for this is simple: G98 is more precise.

Now, this isn't to say that G98 is perfect. There are still some potential inaccuracies that can occur with this method. However, these inaccuracies are generally much smaller than those that can occur with other methods.

So, if you're looking for the most precise CNC machining possible, G98 is the way to go.

G99 should only be used if G98 does not work.

If your cutting tool is mounted in the spindle of your CNC machine and you are using G-code programming to control the machine, you may have to use the G99 command. This is because the G98 command is only meant to be used when the cutting tool is mounted on the table of the machine. The G99 command will cancel any existing G98 commands and initialize the machine to use spindle-based motion.

Fequently Asked Questions

  1. What are the two types of gcodes used to make a tool retract on a CNC machine?

    G11 and G41

  2. What is the difference between G98 and G99?

    G98 is used for facing operations and for roughing and finishing cycles. It tells the machine to move the cutter along the Z-axis only.

    G99 is used for circular interpolation in the XZ plane only.

  3. What is the Z home position?

    The Z home position is the starting point for the Z axis.