Since hole processing is the processing of the inner surface of the part, it is difficult to observe and control the processing process, and its processing difficulty is much 

greater than the processing of open surfaces such as the outer cylindrical surface. The processing process of holes has the following main characteristics:

1) Since most hole processing tools are fixed-size tools, the changes in shape and size caused by tool wear during the processing will directly affect the accuracy of the 

processed hole.

2) Due to the limitation of the small diameter of the hole, it is difficult to increase the cutting speed, which affects the processing efficiency and surface quality.

3) The structure of the tool is limited by the diameter and length of the hole, and the rigidity is poor.

4) When processing holes, the tool generally works in a semi-enclosed space, the chip removal is difficult, the cutting fluid is difficult to enter the processing area, and the 

heat dissipation conditions are not good.

Therefore, in hole processing, the following problems must be solved: cooling problem, chip removal problem, rigidity and guidance problem, speed (efficiency) problem. 

Although the degree of influence of these problems varies in different processing methods, each hole cutting method must be carried out on the basis of solving the above 

corresponding problems.

When drilling a solid, the structure of the drill bit varies with the size and depth of the hole being processed. The most common one is the standard twist drill. When using a 

twist drill, the processing accuracy is generally IT13~IT10, and the surface roughness value is Ra12.5~0.25μm.

When processing existing holes, reaming and boring are representative finishing methods. Reaming is suitable for finishing smaller holes. After reaming, the accuracy can 

reach IT8~IT6, and the surface roughness is Ra1.6~0.4μm, but reaming is generally not efficient. Boring can achieve higher accuracy and smaller surface roughness values. 

Generally, the dimensional tolerance is IT8~IT7, and the surface roughness is Ra6.3~0.8μm. Boring can be performed on different types of machine tools such as lathes, 

drilling machines, milling machines and machining centers.