Practical Knowledge On Screw Applications

1. First, clean any dirt or debris from the surface of the broken bolt stub. Use a center punch to mark the exact center of the fracture surface. Then, using an electric drill fitted with a 6–8 mm diameter bit, drill a hole at the marked center point; ensure the hole goes all the way through. Once drilled through, replace the small bit with a 16 mm diameter bit to enlarge the hole and drill through completely.

2. Select a welding rod with a diameter of 3.2 mm or less. Using low-to-medium current, perform build-up welding inside the drilled hole, working from the inside out; start the welding process at approximately the midpoint of the bolt's total length. When initiating the arc, avoid holding it too long to prevent burning through the outer wall of the bolt. Continue building up the weld until it reaches the top surface of the broken bolt, then extend the weld upward to form a cylinder with a diameter of 14–16 mm and a height of 8–10 mm.

3. After welding, strike the top of the built-up section with a hand hammer to induce axial vibration in the broken bolt. The combination of heat from the arc, subsequent cooling, and the mechanical vibration helps loosen the bond between the bolt threads and the machine body.

4. Observe closely; when slight traces of rust appear at the fracture point after hammering, place an M18 nut over the built-up weld stud and weld the two together.

5. Allow the assembly to cool slightly, then - while it is still warm - fit a box-end wrench onto the nut and twist it back and forth. You can also tap the top of the nut with a small hammer while twisting to help extract the broken bolt.

6. Once the broken bolt is removed, use an appropriate tap to re-thread the hole in the machine frame, thereby clearing out any rust or debris.