When conducting core drilling with a diamond core drill bit, it is essential to pay attention to the coordination between the drill bit and the reamer. A reasonable matching strategy should include the following key points:

Sequential Use Based on Formation and Depth
According to the rock formation and the designed drilling depth, diamond core drill bits and reamers should be used in sequence. Begin with a larger outer diameter, followed by a smaller outer diameter. Likewise, start with a smaller inner diameter, and then use a larger inner diameter. During the rotation process, ensure that all selected drill bits and reamers can reach the bottom of the hole without difficulty, to prevent scouring or core residue issues.

Precise Measurement After Pulling Out the Drill
After retrieving the drill, it is necessary to use a vernier caliper for accurate measurement of both the outer and inner diameters of the drill bit and reamer, as well as the height of the diamond-impregnated bit. These measurements should be carefully recorded to serve as a reference for selecting the appropriate bit size in the next drilling cycle.

Optimal Reamer Diameter Relative to the Drill Bit
The outer diameter of the reamer should be 0.3–0.5 mm larger than that of the diamond drill bit. In hard rock formations, the difference should not exceed 0.3 mm. If the reamer’s outer diameter is too large, it will increase the borehole diameter and accelerate wear, leading to reduced drilling efficiency. Conversely, if the reamer’s outer diameter is too small, it will fail to effectively expand the borehole and protect the bit’s diameter. Therefore, the reamer’s outer diameter must be properly selected relative to the drill bit.

Compatibility between Drill Bit Inner Diameter and Spring Washer
The inner diameter of the drill bit should be compatibly paired with the free inner diameter of the spring washer. If the spring washer’s free inner diameter is too large, it may fail to securely grip the core, resulting in core drop or excessive core residue. If the free inner diameter is too small, it may cause core blockage. Therefore, before lowering the drill, it is essential to check the compatibility between the bit and the spring washer. It is recommended to keep 2 to 3 sizes of spring washers on hand for proper selection and matching.