Use of countersunk screws

Countersunk head screws are mostly used after installation, the surface of the parts can not be raised, and the fastened parts have two thicknesses, the so-called thick, which means that the thickness of the fastened part is greater than the thickness of the head of the countersunk screw Thickness, after the screw is tightened, there is still a part of the screw thread that does not enter the threaded hole, as shown in the figure on the 8th floor, in this case, the countersunk screw can definitely be tightened. There is usually another situation, that is, the thickness of the fastened parts is less than the height of the head of the countersunk screw, which is common in sheet metal parts in mechanical equipment, such as the connection of the hinge of the chassis and the door and the box; the sheet metal of the equipment The connection between the cover and the equipment, etc. Due to the small thickness of the part, the screw through hole of the fastened sheet metal part has become a conical hole completely. In this case, when the countersunk screw is tightened, the screw head is not a conical surface to compress the sheet metal part. , But the bottom of the screw head and the top of the threaded hole are squeezed. Although the screw feels that the screw is tightened, the sheet metal part is stuck instead of being pressed. In this case, although the screw feels that the screw is tightened, the sheet metal The gold piece is indeed not tightened. This is a very common situation. +J#c(sI,a.f (Guide: Briefly describe what should be paid attention to when purchasing bolts/nuts for pipe fittings)

Let me talk about the reason for processing: the head cone of the countersunk screw has a 90° taper angle. Usually the top angle of the newly purchased drill bit is 118°-120°. Some workers who lack training do not know this at all. The angle is poor, and the hole is often directly reamed with a 120° drill. This causes the conical surface of the head to be difficult when the countersunk head screw is tightened, but the line at the bottom of the screw head is difficult. This is also the so-called countersunk screw cannot be tightened. One reason is that it is not the fault of the screw.

In summary, the use of countersunk screws should pay attention to: 1. The taper of the reaming hole should be 90°, and it must be guaranteed that it should be less than 90° rather than greater than 90°. This is a key trick. 2. If the thickness of the sheet metal is less than the thickness of the head of the countersunk head screw, you can replace the screw with one size smaller, or it is better to ream the hole smaller than ream so that the diameter of the bottom hole becomes larger and the parts are not tight. 3. If there are multiple countersunk screw holes on the part, be more precise when processing. Once the drill is crooked, the assembly will be difficult to see, but as long as the error is not large, it can be tightened, because when tightening, if the diameter of the screw is not very Large (approximately no more than 8mm), when the hole pitch has an error, the screw head will be deformed due to the force when it is tightened or it will be tightened.

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