Through the analysing of mechanism of breaking rock in a hole explosion, the principle and design method of a crushing blasting is expounded.

The breaking and milling tool is a special tool used which is used to cut and mill a section of casing in hole so that sidetrack drilling operation can be done smoothly.

Now and again a hole gave the first sledge a jolt; the next was jolted in just the same way, and the next, and the sledges followed one another, rudely breaking the iron-bound stillness.