What is Metrology?
The word, “metrology,” is derived from Greek and essentially means the study of measurement. Metrology originally stemmed from the need to manufacture interchangeable parts. To make that possible, the dimensions of all the parts had to fall within a specific range — otherwise, they simply wouldn’t fit their companions. In its modern application, metrology has become a highly advanced field with many tools and statistical methods to measure the accuracy and quality of manufactured parts.
Key Concepts in Metrology
To understand metrology it is important to know the difference between tolerance, precision, accuracy, and uncertainty.
Tolerance
Tolerance is the variation within a part's dimensions that is considered acceptable. It is essential to understand the part's function before settling on the required tolerance. For example, a shaft that fits into a bearing needs a tighter tolerance than a through-hole for a bolt. A little extra space around the bolt isn't harmful, but too much wiggle room for the shaft will enable dangerous oscillations.
Another factor to consider is the manufacturing machine's ability to achieve these tolerances; some CNC machines can manufacture parts to a tolerance of a few microns while others are nowhere near such precision. Metrology techniques verify that a manufactured part fits within its specified tolerance. Tolerances for manufacturing processes can be found in Xometry's Manufacturing Standards.
Accuracy
In mathematical terms, accuracy is defined as how close the average of a set of measured values is to the reference value, X. In manufacturing, this could show as the difference between the actual produced product and the CAD model or technical reference drawing.
Precision
Precision refers to how close each measurement is to the average of the measured values. This is expressed statistically in terms of the standard deviation (
Keyword: cnc routing wood