1. For self tapping screws that are broken inside walls or wooden blocks, you can first use a grinder to smooth out the broken part, prepare a small drill bit to drill first, and then change it to a larger drill bit. Wait until the broken part gradually falls off, and use a tap to tap the thread, so that the self tapping screw that is broken inside can be screwed out. In addition, an iron rod can be welded onto the broken surface and then twisted out in a counterclockwise direction.
2. If the self tapping screw is not too hard, first chisel the surface flat, make a small hole from the middle part, drill with a drill bit, and then use a broken wire extractor in a vertical direction to unscrew in the opposite direction.
3. If the self tapping screws have rusted, they cannot be removed using the above methods. You can grill it over fire and then add lubricating oil. By using the principle of thermal expansion and contraction, you can also remove the self tapping screws. If it still cannot be removed, it is necessary to smash a relatively large hole, damage the wall or wooden product, and repair it later.