1. concept of tool length Tool length is a very important concept.
When we CNC machining program a part, we must first specify the programming center of the part, and then we can establish the workpiece programming coordinate system, and this coordinate system is only a workpiece coordinate system, the zero is generally on the workpiece. Length compensation is only related to the Z coordinate, it is not like X, Y plane programming zero, because the tool is positioned by the spindle cone hole does not change, for the Z coordinate zero is not the same. The length of each knife is different.
For example, CNC machining will drill a hole with a depth of 50mm, and then tap the hole with a depth of 45mm, using a drill with a length of 250mm and a tap with a length of 350mm. At this time, the machine has set the zero point of the workpiece. When the tap tapping is replaced, if the two knives start from the set zero point, the tap tapping is too long because it is longer than the drill, which will damage the tool and the workpiece. At this time, if the tool compensation is set, the length of the tap and the drill is compensated. At this time, the zero point of the machine is set, even if the length of the tap and the drill is different, because of the existence of compensation, when the tap is called to work, the zero point Z coordinate has automatically compensated the length of the tap to Z+ (or Z), to ensure the correct processing zero point.
2. Tool length compensation in CNC machining is achieved by executing commands containing G43 (G44) and H, and we give a Z-coordinate value so that the tool moves to a distance Z from the workpiece surface after compensation. The other instruction G49 is to cancel the instruction G43 (G44), in fact, we do not need to use this instruction, because each tool has its own length compensation, when changing the tool, the G43 (G44) H instruction is used to give its own length compensation and automatically cancel the length compensation of the previous tool.
3. Two ways of tool length compensation
1) In CNC machining, the actual length of the tool is used as the compensation of the tool length (this way is recommended). To USE the tool length AS COMPENSATION is to measure the length of the tool using a tool counter, and then input this value into the tool length compensation register as the tool length compensation. The reasons for using tool length as tool length compensation are as follows:
Firstly, using the tool length as the tool length compensation can avoid constantly modifying the tool length offset in different workpiece processing. In this way, a tool can be used on different workpieces without modifying the tool length bias. In this case, in accordance with certain rules of the tool number, to each tool file, with a small sign to write the relevant parameters of each tool, including the length of the tool, radius and other information, in fact, many large mechanical processing enterprises on CNC machining equipment tool management are using this method. This for those who have a special tool management department of the company, it is not necessary to tell the parameters of the tool face to face with the operator, and even if the tool is removed due to the capacity of the tool store and the next time to reload, only according to the knife length value on the sign as the tool length compensation and do not need to be measured.
Secondly, the use of tool length as the tool length compensation, can let the machine tool side processing operation, while the length of other tool measurement on the tool instrument, and not because of the tool on the machine tool and occupy the machine tool running time, so that can give full play to the efficiency of the machining center. In this way, when the CNC machining spindle moves to the programming Z-coordinate point, it is the Z-coordinate value after the spindle coordinate plus (or minus) the tool length compensation.
2) The distance between the tool tip in the Z direction and the programming zero of the CNC machining (positive or negative) is used as the compensation value. This method is used when the machine is operated by only one person and there is not enough time to measure the length of the tool using the tool setter. In this way, when using a knife to process another workpiece, the tool length compensation should be reset. When the tool length is compensated by this method, the compensation value is the tool tip movement distance when the spindle moves from the zero of the Z coordinate of the machine tool to the programming zero of the workpiece, so the compensation value is always negative and large.
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