Machining accuracy is the actual size, shape and position of the three geometric parameters of the surface of the parts after processing and the degree of conformity with the ideal geometric parameters required by the drawings. Machining accuracy is measured by tolerance grade. The smaller the grade value, the higher the accuracy. The machining error is expressed by numerical value. The larger the value, the larger the error. High processing accuracy means small processing error and vice versa.
The ideal geometric parameter is the average size for the size; for the surface geometry, it is an absolute circle, cylinder, plane, cone and straight line; for the mutual position between the surfaces, it is absolute parallel . Vertical. Coaxial. Symmetrical, etc. The deviation of the actual geometric parameters of the part from the ideal geometric parameters is called machining error.
The actual parameters obtained by any processing method will not be absolutely accurate. From the function of the part, as long as the processing error is within the tolerance range required by the part drawing, the processing accuracy can meet the requirements.