During the construction process, small rotary drilling rigs often encounter difficulties in drilling at the bottom of the hole due to slipping, which can be attributed to the following five reasons:

1. Mud reasons:

Construction on sub-clay layers often results in slipping due to the increased concentration and specific gravity of the mud when reused. This leads to floating drilling where the drill bit cannot reach the bottom of the hole. Forcing the drill bit to the bottom, the high rotation speed of the drill bit causes the mud to act negatively, lubricating the cutting surface between the bottom clay and the drill teeth.

2. Drilling tool reasons:

Slippage can occur due to a series of reasons such as the drill bit and drill rod being off-center, the drill tooth angle being less than 45 degrees, improper center cone, too dense tooth arrangement, and severe wear of the drilling tool.

3. Geological reasons:

Some geological formations are mudstone with not very high compressive strength, around 550Kp, but are very dense and slippery when wet. To solve mudstone slipping, it is necessary to thoroughly address the above three reasons and put effort into the selection of drill bits. This requires the operator to have certain construction method experience.

4. Reasons related to the drilling machine itself:

The power head rotates too fast without a gear for slow speed, structural reasons, insufficient pressing force, and a certain degree of bending in the drill rod from long-term use can also cause slipping.

5. Improper operating techniques can also lead to slipping:

Over-digging during drilling and forcibly leveling the bottom of the hole can cause the next drilling to slip. Not completely closing the bucket door when lifting the drill bit, causing a large amount of soil from the bucket to fall into the bottom of the hole, is also a reason for slipping. Starting the rotation too quickly, causing the drill to become stuck, the rational selection of operations and drill bits is the basic solution to slipping.