Alloy drill bits are used for soil and a small amount of stones. They cannot be used on mountains or rocks, granite, etc.

Very solid rock f=15~20 (solid granite, limestone, quartzite, etc.).

 Hard rock f=8~10 (such as unstable granite, solid sandstone, etc.).

 Medium solid rock f=4~6 (such as ordinary sandstone, iron ore, etc.).

 For unstable rocks, f=0.8~3 (such as loess, only 0.3).