In CNC machining, using G53 back to the origin instead of G28

Returning to the origin (also called zeroing) is an operation that must be completed every time the machining center is turned on. This seemingly simple action is very important to the machining accuracy. Every time we use the caliper, we will reset the caliper to zero, or use the gauge block to calibrate the caliper. This is to have a fixed reference object for the caliper, and compare the measured data with the actual data of the gauge block. , So as to distinguish whether the caliper is accurate and whether it can be used normally.

The same is true for the machine. A fixed and precise switch is set on each axis of the machine. When this switch is triggered, it means that the machine has returned to that specific position at this time. Actions can be based on this point as a reference. Even if there is a power failure during processing, the specific point can be found by performing the operation of returning to the origin again to ensure the consistency of the reference point position, thereby accurately connecting the previous processing path.

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The control system of the machine tool will also require a return to origin operation after the power is turned on again, otherwise the automatic processing function of the machine will be unavailable, and the control system will also issue a warning of “no return to origin” on the display until each movement of the machine tool The axis can accurately stay at that specific reference origin, otherwise the warning will continue.

Since the service life of the switch will be affected by the external environment, the position of the origin will also change after maintenance or other reasons cause the replacement of the origin switch. At this time, a new origin will be generated, and all subsequent actions will be based on This new reference origin, the coordinate position set before the new reference origin, no longer coincides with the current coordinate position.

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For example:

Before the origin switch was replaced, a workpiece was being processed on the machine tool, and the workpiece coordinate G55 was used. After the origin switch is replaced, if you want to continue processing this workpiece, you need to reset the G55 coordinates. This is because the previous G55 refers to the original origin coordinates, and now this origin has been offset, and all movements since then will refer to this new origin coordinates, so the coordinates of G55 must be reset. Continue to execute the processing program.

In the process of returning to the origin, we should also pay attention to the movement speed and movement sequence of each axis.

The system defaults to return to the origin at the moving speed of G00 (rapid traverse mode). Each axis of the machine will move independently, and the moving speed is the highest speed preset by each axis. In order to meet various needs, here The rapid traverse speed can also be adjusted by the rapid traverse button.

The system returns to the preset movement sequence in the process of returning to the origin. For the VF-2 machining center, usually the Z axis moves first, and then the X axis and Y axis move at the same time. The priority of the X-axis and Y-axis is the same. Due to the different distances from the origin, the time it takes for the X-axis and Y-axis to return to the reference point will be different. This is likely to have a different rapid traverse trajectory than you expected. Causes a major loss in safety, so it is necessary to spend time to understand the movement sequence of each axis movement.

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In the general G codes, G53 and G28 have the function of returning to the origin, and they can only be used with G91 (incremental value mode) at the same time.

G91 (incremental value mode) and G90 (absolute value mode) are a group of modal codes. “Modal” means that once a code is declared valid, it will always be stored in the register. Regardless of whether the next program line contains this code or not, the system will default that this code is always valid. Unless another code of the same group is declared valid, replace the value stored in the register.

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The difference between G53 and G28 is:

G53 is to directly return to the reference origin;

For G28, it is necessary to first return to the origin of the current coordinate system, and then return to the reference origin.

From the perspective of safety and efficiency, we strongly recommend that you use G53 to return to the reference point.