Precision + Repeatability = Accuracy
The issue of machine tool accuracy is frequently raised in our day-to-day communications with customers. We believe the following is the correct answer for the CNC machines.
The precision is the ability to perform fine movements that means the smallest incremental movement that a machine can achieve.
The Repeatability is the consistency that means the good repeatability equals consistent results every time when they are performed by the same operator, with the same instrument or machine, and under the same conditions.
The Accuracy is the result of combining precision and repeatability correctly which is the degree of closeness between a measured value and its true value.
Smartech-CNC boasts over 30 years of experience in manufacturing high-quality machine tool frames.
We believe the mechanical structure is the fundamental guarantee of machine tool accuracy.
The pictures in the article show the standard machine tool frames we currently supply
Understanding the Causes of Inaccuracy
When we troubleshoot CNC accuracy issues, it is crucial to establish which of the three terms (precision, repeatability and accuracy) is affected.
Factors Affecting Precision
The machine's ability to make precise cuts limits precision. Common causes include:
- Uneven rotation of the tool
- Discrepancies between the actual tool dimensions and the dimensions used in softwore.
- Incorrect step/microstep settings on motor drivers
- Mechanical ratio errors in drive systems
- Wear or loose-fitting drive components
Factors Affecting Repeatability
Repeatability issues can result in inconsistent part sizes or prevent the machine from reliably returning to the same position.
- One of the most frequent issues is the loose mechanical linkages.
- Variable drive system performance across the table.
- Drive system harmonics
- Thermal expansion/contraction of components
- Lost steps
Factors Affecting Accuracy
Inaccuracies in the design specifications prevent the machine from consistently producing parts that match them.
- Wear or degradation of drive components
- Uncalibrated machines
- Incorrect software offsets
- Inaccurate machine zeroing
- Incorrect software scaling
- Mismatched units
- Errors in step-per-inch calculation.
Common Misuses
Precise but not repeatable or accurate
A precise machine can perform fine movements, but if it lacks repeatability, the parts it produces may not fit together. For example, if the machine shifts slightly between cuts, one side of a part may end up longer than the other, even though the movements themselves are precise.
Repeatable but not precise or accurate: A repeatable machine produces consistent parts; however, if it lacks precision, all of those parts will be incorrect in the same way. For example, every part might be same smaller than the design, meaning they fit together, but the final product is the wrong size.
Smartech-CNC not only provide standard machine tool frames, but also offer customized solutions.
We are willing to talk with customers, explore new concepts and new technologies, and jointly elevate machine tool accuracy to a higher level.
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