Countersunk screws, also known as flat machine screws or flat head screws, have a 90 degree cone at the head and a 90 degree conical groove on the surface of the mounting hole on the connector. This ensures that the screw head is parallel to the surface of the connector and is used for areas where slight protrusions are allowed on the surface. Why do we always encounter the phenomenon of not tightening during use?
Today, Jinrui will share with you the reasons and precautions for not tightening the sinking head screw:
Reason 1: The thickness of the tightened part is greater than the thickness of the countersunk screw head. After tightening the screw, there is still a portion of the screw thread that has not entered the threaded hole. In this situation, the countersunk screw can definitely be tightened.
Reason 2: The thickness of the tightened part is less than the height of the countersunk screw head, which is common in sheet metal parts in mechanical equipment, such as the hinge of the chassis and the connection between the door and the box; The connection between the sheet metal cover of the equipment and the equipment, etc.
Due to the small thickness of the parts, the screw through-hole of the tightened sheet metal part becomes a completely conical hole. In this case, when the countersunk screw is tightened, the screw head does not press against the sheet metal part with a conical surface, but rather the bottom of the screw head and the top of the threaded hole are squeezed. Although the screw feels tightened, the sheet metal part is stuck instead of pressed. In this case, although the screw feels tightened, the sheet metal part is indeed not tightened. This is a very common situation.
Reason 3: The head cone of the countersunk screw has a 90 ° conical angle, while the top angle of newly purchased drill bits is usually 118 ° -120 °. Some untrained workers are unaware of this angle difference and often use a 120 ° drill bit to expand the hole directly. This causes the tightening of the countersunk screw not to be difficult on the conical surface of the head, but on a line at the bottom of the screw head, which is also one of the reasons why the countersunk screw cannot be tightened.
Kind reminder:
1. The taper of the hole should be 90 °, and it should be guaranteed that it is better to be less than 90 ° than to be greater than 90 °. This is a crucial trick.
2. If the thickness of the sheet metal is less than the thickness of the countersunk screw head, it is possible to replace it with a smaller screw, or it is better to enlarge the hole smaller.
