Causes of machining errors in the inner hole of CNC lathes
When CNC lathes use the same turning tool to machine two inner holes with large diameter differences, it often appears that the machining size of one hole is accurate and consistent with the programmed value, but the machining size of the other hole is larger than the programmed size. Excluding the cause of the failure of the CNC lathe itself and the processing technology of the parts, what else causes the error?
Compared with the outer circle machining on the CNC lathe, there are more influencing factors. For example, the length of the tool holder is long, the diameter is small, the rigidity is poor, the cooling and chip removal are difficult, the height of the tool tip and the axis of the machine tool is not well controlled, and so on. At the same time, the machining accuracy of the hole is required to be higher.
Before turning on a CNC lathe, the tool tip and the axis of the machine tool spindle must be adjusted to the same height when installing a turning tool. For the inclined bed CNC lathe, the relative height of the turret and the axis of the machine tool spindle is strictly required during manufacturing. As long as the standard tool is used, it is not necessary to adjust the height of the tool tip. Most machine tool manufacturers do not have a unified standard for the relative height of the tool post and the axis of the spindle of the flat bed CNC lathe. The height of each machine is different. Even if the standard tool is used, the height of the tool tip must be adjusted with a spacer.
In the actual machining process, machining errors rarely occur on the outer surface of the stepped shaft. The main reason is that the operator can check whether the tool center height is consistent with the spindle by trial cutting the end face, which is convenient for measuring the tool tip deviation, and there are fewer machining errors and easy to solve . However, there are many reasons for machining errors when machining stepped inner holes, and it is difficult to find the causes of errors. The operator usually thinks that it is a problem with the accuracy of the machine tool. It is difficult to adjust the inner hole turning tool. Sometimes the processed hole is relatively small. In order to avoid the collision of the tool bar with the workpiece hole, the tool is often installed higher. In this case, the machining diameter of the tool segment is accurate, and machining dimensional errors will occur if stepped holes are machined.
This situation occurs mainly in the process of tool setting. The tool setting for external machining will perform a trial cutting end face to check whether the tool center height is consistent with the spindle, which is convenient for measuring the tool nose deviation, so that there are fewer errors; but machining holes Since it is impossible to test the tool center height by cutting the end face during tool setting, most of them are directly measuring the diameter of the inner hole, so the diameter of the tool section is accurate, but the height of the tool center is inconvenient to measure. Use this kind of tool that has a height difference to process other tools. The diameter of the inner hole will cause errors.
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