Three different measurements determine the overall accuracy of a CNC milling parts: positional accuracy, precision or repeatability, and tolerance.
1. Mill position accuracy
Position accuracy is the difference between the specified distance between points on the part and the actual measured distance of those points after milling. For a milling machine that CNC milling parts, accuracy depends on its ability to follow its programmed path. The machine shop determines the accuracy of the rolling mill by taking multiple measurements and calculating the statistical average of the deviations.
2. Repeatable accuracy
The machine shop defines the accuracy of the milling machine by repeating the same commands exactly so that one part after the other provides the same result. Similar to accuracy, a shop can calculate the accuracy of a milling machine that CNC mills a part by taking multiple measurements when commanding the machine to cut a path. The measure of accuracy is the repeatability of cutting the same exact path, ultimately producing an exact copy of the part over and over.
3. Finished product tolerance
Machinists and engineers use the term tolerance when referring to the amount of allowable deviation from the measurement settings of a CNC milling parts. CNC programmers and machinists program milling machines to manufacture parts within the tolerances required by customers. When cutting material and producing parts, the milling machine should stay within the set tolerances of the specified measurements.
