We deal with machining every day, and we often mention machining accuracy. But, when you say precision, are you really right? Let's take a look at the "machining accuracy" today!
01
The difference between precision and precision
Accuracy means the correctness of the measurement results, and precision means the repeatability and reproducibility of the measurement results. Precision is the prerequisite for accuracy. The figure below is a good illustration.
Accuracy
Refers to the degree of closeness between the obtained measurement results and the true value. The high measurement accuracy means that the systematic error is small. At this time, the average value of the measurement data deviates from the true value less, but the data is scattered, that is, the size of the accidental error is not clear.
Precision
Refers to the reproducibility and consistency between the results obtained by repeated measurements using the same spare sample. It is possible to have high precision, but the precision is not high. For example, the three results obtained by using a length of 1mm for measurement are 1.051mm, 1.053, and 1.052 respectively. Although they have high precision, they are not accurate.
02
Definition of Machine Tool Accuracy
When you compare CNC machine tools, if the "positioning accuracy" of the sample of A machine tool factory is marked as 0.002mm, and the "positioning accuracy" of the sample of B machine tool factory is marked as 0.004mm. Through these two intuitive data, you will naturally think that the machine tools of A machine tool factory are more accurate than B machine tool factory.
However, in fact, it is very likely that the machine tools of B machine tool factory are more accurate than A machine tool factory. The problem lies in the standard of their precision definition. Therefore, when we talk about the "accuracy" of CNC machine tools, we must clarify the definitions and calculation methods of standards and indicators.
Generally speaking, accuracy refers to the ability of the machine tool to locate the tool nose point to the program target point. However, there are many ways to measure this positioning ability, and more importantly, different countries have different regulations
