1. For machining, machining accuracy refers to the tolerance range between the actual value after machining and the theoretical value of the design.

Measurement accuracy is how close the measured value is to the true value. Contains both precision and accuracy.

2. The precision is 3 ~ 0.3 μm, and the roughness is Ra0.3 ~ 0 · 03μm called precision machining;

 Accuracy of 0.3 to 0.03 μm, roughness of Ra 0.03 to 0.005 μm is called ultra-precision machining, or sub-micron machining;

 The precision is 0.03 μm (30 nm), and the roughness is better than Ra0.005 μm. It is called nanometer (nm) processing. 3. The most widely used ultra-precision machining processes include car, grinding, grinding and polishing.

4. The surface finish of the problem is 0.8. If it is the Ra value, it can be regarded as precision machining. If it is the Rz value, it is ultra-precision machining.

5. Flatness 0.01, depending on the size of the workpiece, if it is a small piece of 10 mm or less, it is not a precision machined part. Refer to the tolerance accuracy rating table for details.

6. In machining, the tolerance indicates the manufacturing accuracy requirements of the part, reflecting the ease of processing.

The tolerance grade is divided into 20 levels of IT01, IT0, IT1, ..., IT18, the grades are sequentially reduced, and the tolerance values are sequentially increased.

IT4~IT5 super finishing, IT6~IT7 finishing, IT8~IT10 semi-finishing, IT11~IT13 roughing.