Difference Between Precision and Accuracy | Accuracy, Precision and Tolerance in CNC Machining | CNCLATHING


To evaluate the measurement results in CNC machining, precision and accuracy are two commonly used concepts. In this article, let’s learn about the precision and accuracy definition, what is the difference between precision and accuracy, as well as the relationship between accuracy, precision and tolerance for machined components.


How to Define Precision and Accuracy – What are Precision and Accuracy?

Precision refers to the closeness of the measurements to each other, which means that if the measured values are all close to each other, then they are precise. The certain value should be repeatedly measured by the same method under the same conditions. It reflects if the measured value is repeated and consistent. The higher the precision, the more close the results are. The CNC machining precision express the reproducibility of the measured diameter, length, and other values of the machined part and reflect the influence of accidental error. Precision machining typically refers to a machining process holding close tolerance or to remove material and create machined parts with tolerances in small range.


Accuracy is defined as the closeness of the measurements to a specific value or true result. If the measurements are all close to the true value, so they are accurate. It can reflect the influence of system error. If the system error is small, the accuracy is high. A successfully fabricated workpiece should have both high accuracy and precision.


The Difference Between Precision and Accuracy

Accuracy and precision are both reflect how close a measurement is to an actual value, but different considerations should take when evaluating them due to precision and accuracy difference.
Accuracy refers to the degree to which the average value of multiple measurements under certain experimental conditions is consistent with the true value. While precision refers to the consistency (conformity) between all measured values after repeated measurements under the same conditions.
Accuracy reflects system error, while precision reflects random error.
3)Measurement times
Accuracy can be observed by one measurement while many measurements are needed to assess precision.


What’s the Relationship Between Accuracy, Precision and Tolerance?

What we should note is that high precision not means high accuracy, and even if the measurement is accurate, not presents it’s precise. Maximum accuracy is not necessary for lots of applications, because it means more cost and time investment. Modern CNC machine and cutting tools are accurate enough for most projects. Precision is the main factor you should consider when choosing a CNC machining manufacturer, it related to the product quality. There are four situations of your CNC machined part:

– High accuracy, high precision

– High accuracy, low precision

– Low accuracy, high precision

– Low accuracy, low precision


In addition, the precision is measured by specifying tolerance. The tolerance specifies the deviation away from a known value, expressed as a “+/-” number, such as +/-0.005. Reasonable tolerances are allowed for CNC machine tools for natural movement.