What is Tool Offset in CNC Milling?
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What is Tool Offset in CNC Milling?

Views: 1399     Author: Site Editor     Publish Time: 2019-05-07      Origin: Site


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Tool length offsets are one of the most widely misunderstood aspects of CNC mill operation. In this article, we will help you know more about tool offset in CNC milling and have a clearer mind about what is tool offset and how to use it correctly.


1. The definition of tool offset in CNC milling

2. Tool length compensation

3. Offset table

4. G codes for tool length compensation

5. Method of tool offset in CNC milling

6. After measurement


The definition of tool offset in CNC milling

The term offset is used to describe the tolerance of the tool diameter and length of the workpiece to be cut by an exponentially controlled machine tool. CNC machine programming is always based on the central point of the tool. The tool runs along the programming line.

In the most basic sense, the offset is the machine tool controller's "understanding" of the tool and the workpiece. Technically, offsets are Numbers stored in specific registers in the controller memory. If no offset value is set, the tool will move according to the center of the tool, not according to the tool used. This means that the tool will cut the wrong part of the workpiece. Because the diameter and length of the tool may be different, you need to set the "offset" value to move the tool to the correct position to cut.

Like the memory of an electronic calculator, offsets in the CNC control are stored locations into which mathematical values can be entered. Just as the value in the memory of a calculator has no sense until referenced by its operator in a calculation, the value contained by an offset of the CNC regulator does not have any significance until it is referenced by a CNC program. From the marksman analogy, one can think of the values deposited in CNC offsets as the sum of modification necessary on the prospect of the search needed to compensate for detachment to the aim. Remember that the rifle only requires alteration for one resolution, to modify for the detachment to the aim. With most CNC machine tools, it is necessary to have at least one offset for each tool.


Tool length compensation

On some CNC machines, you may need to enter the radius value of the tool. This is called tool length compensation. The use of tool length compensation varies depending on the machine controller.

Most controllers use three G codes for tool radius compensation:

G41 - executes tool length compensation to the left.

G42 - executes tool length compensation to the right.

G40 - Cancels tool length compensation.

To determine whether to use the left (G41) or right (G42) tool radius compensation, you need to see the direction of tool movement during the machining operation.

Also, you can use the offset value (G43) to adjust the tool length of the tool.


Offset table

Most CNC machine tool controllers have an offset table input by the operator. Here is an example of a table showing how to organize offset values to illustrate tool length (G43) and tool length compensation for four different tools.


Tool length

Radius compensation




























The values of offset numbers 1-4 refer to the tool length of each of the four tools, and the values of offset numbers 11-14 refer to the radius compensation of each of the four tools.


G codes for tool length compensation

Tool length compensation uses three G codes - G43, G44 and G49 - plus H code.

· When length compensation is activated (selected by G43 or G44), the H code tells the control the length offset to use.

· G43 tells the control to start applying length compensation by adding the current length offset (selected by the H code) to all Z-axis positions.

· G44 is a substitute for G43, so it's almost never used. It informs the controller to apply tool length compensation by subtracting the current length offset from all z-axis positions.

· G49 tells the controller to stop applying length compensation.

· H0 is a special H code. It specifies a length offset value of zero, which means that the offset will not be applied even if G43 is active.


Method of tool offset in CNC milling

· Don't use length compensation if you rarely use more than one tool in a job.

· Use a dedicated reference tool if you have several tools you wish to set up, keep, and reuse, but you do not have a consistent tool measuring surface.

· It is convenient to use your touch probe.

· If you want to set up, save, and reuse multiple tools, use an imaginary reference tool. You have a consistent tool for measuring surfaces.

· Use a normal tool from each job as a reference tool.

· Instead of using reference tools, use length offsets to locate parts. If you have to measure each tool anyway (because they are not in the tool container), then this is a reasonable approach.


After measurement

After the measurement, the offset is stored in the machine memory. Each machine usually has a set of memory registers for tool compensation numbered starting from 1. It's not uncommon for a machine to "remember" information about more tools, because it can be physically maintained at a time, so you can quickly switch jobs. The zero offset is also stored in the specific memory location of the machine controller. It is often the case that the machine controller can "remember" more than one hundred offset positions at the same time. This allows multiple fixtures to be set at the same time, so you don't have to measure the offset each time you change it.


This paper discusses the basic information of tool compensation in CNC milling from the definition of tool compensation, the content of tool length compensation, the method of tool compensation and the content after measurement. Hope you can learn more about nc milling tool offset knowledge.


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