What You Need to Know About CNC Machining Precision

We are exposed to processing every day, and we often mention CNC machining precision in this process. But is your machining accuracy correct? Or do you mean “rigorous”?  Today, Yijin hardware experts will tell you the knowledge about CNC machining parts precision!

The so-called CNC machining precision refers to the actual size, shape, and position of the CNC machined part surface and the ideal geometric parameters required by the drawing! For ideal geometric parameters, the CNC machining accuracy of dimension refers to the average size; the precision CNC machining accuracy of shape refers to absolute circle, cylinder, plane, cone, and straight-line; the custom machined parts accuracy of mutual position refers to absolute parallelism, verticality, coaxiality, symmetry, etc.

CNC precision parts manufactured by YIJIN Hardware

1. CNC Machining Dimension Accuracy

The so-called dimensional accuracy refers to the correspondence between the actual size of the CNC turning parts after processing and the tolerance zone center of the CNC turning parts size.

2. CNC Machining Shape Accuracy

The so-called shape accuracy refers to the degree of the actual geometry shape of the machined parts surface and the ideal geometric shape.

3. CNC Machining Position Accuracy

The so-called position accuracy refers to the actual position accuracy difference between the relevant surfaces of precision machining parts.

4. CNC Machining Interrelation

When designing machine parts and specifying the machining precision of parts, it is usually necessary to control the shape error within the position tolerance, and the position error should be less than the dimension tolerance. This means that the shape accuracy of precision parts or important surfaces of CNC parts needs to be higher than the position accuracy requirements, and the position accuracy requirements need to be higher than the dimensional accuracy requirements.

The so-called machining error refers to the deviation between the actual geometric parameters and the ideal geometric parameters. Among them, the size of CNC machining error reflects the level of CNC machining accuracy, the larger the error, the lower the CNC machining accuracy; the smaller the error, the higher the CNC machining accuracy.

Brief Introduction to Machining Precision

“Machining accuracy” is a term, which is mainly used to produce CNC products. Both CNC machining accuracy and CNC machining error are used to evaluate the geometric parameters of CNC machined parts surfaces. Among them, the CNC machining accuracy needs to be measured by the tolerance grade. The smaller the grade value is, the higher the CNC machining accuracy is; while the machining error is expressed by numerical value, and the larger the value, the greater the error; That is, the higher the CNC machining accuracy, the smaller the machining error, and the lower the CNC machining precision, the higher the machining error.

There are 20 tolerance levels, from IT01, IT0, IT1, IT2, IT3 to IT18. Among these grades, IT01 indicates that the machining accuracy of the part is the highest, IT18 indicates that the machining accuracy of the part is the lowest, and generally, IT7 and IT8 are the intermediate grades of CNC machining accuracy.

It should be noted that no matter what processing method is used, the actual parameters obtained will not be absolutely accurate. From the function of cnc turning machine parts, if the machining error is within the tolerance range required by the custom machined parts drawing, then the CNC machining precision is considered to be guaranteed.

The Difference Between CNC Machining Accuracy and CNC Machining Precision

CNC Machining Accuracy

When the CNC machining accuracy is small, the average value of the measured data deviates less from the true value. But in the case of scattered data, that is, the size of the accidental error is not clear.

CNC Machining Precision

CNC machining precision refers to the repeatability and consistency of the results obtained by repeated determination with the same spare sample. However, there may be high CNC Machining precision, but the CNC machining accuracy is not accurate. For example, if the length of 1 mm is used for measurement, three results will be obtained, which are 1.051 mm, 1.053, and 1.052. Although their CNC machining precision is high, the values are not accurate. Thus, CNC machining accuracy refers to the accuracy of the measurement results, while CNC Machining precision refers to the repeatability and reproducibility of the measurement results. Among them, CNC Machining precision is the precondition of CNC machining accuracy.

CNC precision parts manufactured by YIJIN Hardware

Methods to Improve CNC Machining Accuracy

Adjustment of Process System

1) Adjustment of trial cutting method

Through a series of processes of “trial cutting – measuring size – adjusting cutter’s cutting amount – cutting – re-cutting”, the process can be repeated until the required size is reached. However, the production efficiency of this method is low, so it is mainly used for single-piece and small-batch production.

2) Adjustment Method

The adjustment method obtains the required size by pre-adjusting the relative positions of the machine tool, fixture, workpiece, and tool. However, due to its high cnc turning parts productivity, this method is mainly used for mass production.

Reduce the Error of Machine Tool

1) In order to improve the CNC manufacturing accuracy of the spindle components, the rotation accuracy of the bearing should be improved

①High CNC machining precision rolling bearings are selected;
②high precision multi oil wedge dynamic pressure bearings are used;
③high precision hydrostatic bearings are used

The accuracy of accessories with bearings should be improved

①It can improve the CNC machining accuracy of box support hole and spindle journal;
②It can improve the CNC machining accuracy of the surface matching with the bearing;
③By measuring and adjusting the radial runout range of the corresponding parts, the error can be compensated or offset.

2) Proper preloading of rolling bearings is required

①Clearance can be eliminated;
②Increase of bearing stiffness;
③Homogenize the rolling element error and reduce the transmission error of the transmission chain
1# Fewer transmission parts, short transmission chain, and high transmission precision;
2#Through the use of speed reduction transmission, this can ensure the important principle of transmission CNC machining accuracy. And the closer to the end of the transmission pair, the smaller the transmission ratio;

3) The CNC machining accuracy of the end piece needs to be higher than that of other transmission precision machining parts.

Reduce Tool Wear

It is necessary to regrind the tool before the tool size wear reaches the stage of sharp wear.

If you are interested in our products, you are welcome to send your requirements with your drawings to us via email. We are very glad to give you the most favorable quotation.

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