Reasons and precautions for untightening countersunk head screws

Countersunk head screw is also known as flat machine screw, flat head screw, its head is a 90 degree cone, the mounting hole surface on the connector is also processed with a 90 degree cone socket, so as to ensure that the screw head and connector surface parallel, for the surface can allow a little protruding place. And in the process of our use, why always encounter the phenomenon of not tightening?

Reasons and precautions for untightening countersunk head screws:

Cause 1. The thickness of the fastened part is greater than that of the head of the countersunk screw. After the screw is tightened, some screw threads do not enter the thread holes. In this case, countersunk screws can certainly be tightened.

Reason 2. The thickness of the fastened part is less than the height of the countersunk screw head, which is commonly seen in sheet metal parts in mechanical equipment, such as the connection between the hinge of the case and the door and the box; The connection between the sheet metal cover and the equipment and so on.

Due to the small thickness of the parts, the fastening sheet metal parts, screw through the hole completely into a conical hole, in this case, when the countersunk screw is tightened, the screw head is not conical compression of the sheet metal parts, but the screw head base and the top of the threaded hole squeeze, although the feeling of the screw is tightened, but the sheet metal is stuck rather than pressed, in this case, although the feeling The screws are tightened, but the sheet metal is really not tightened. This is a very common situation.

Reason 3, countersunk screw head round vertebral body is 90° conical Angle, usually the top Angle of the newly bought drill is 118°-120°, some lack of training workers do not know this Angle difference, often directly with 120° drill hole, which causes countersunk screw tightening is not the head conical surface, but a line at the bottom of the screw head is difficult, this is also called One of the reasons countersunk screws don't hold.

Warm reminders need to pay attention to:

1, reaming taper should be 90°, to ensure that it is better than 90°, but not greater than 90° this is a key trick.

2. If the sheet metal thickness is less than the thickness of the countersunk screw head, you can change a smaller screw, or prefer smaller reaming.