The reason why the inner wall of the drilled hole is not smooth is that the processing technology is not arranged properly. If you want the drilled hole wall to be smooth, the hole must be processed multiple times. If the hole wall requirements are not too high, drill the bottom hole first, and then expand the hole to the size. This will make the hole wall smoother than drilling it directly. If the hole wall requirements are high, another process will be added to ream the hole. When reaming, leave a machining allowance for reaming, so that the surface roughness of the processed hole wall will be very high.