unscrewing fastener - "click" sound

[cervantes]

Hi all,

is my thesis appropriate regarding this sound in your opinion?

if you are trying to unscrew a screw with a tool there is always a characteristic "click" sound. After that, you can do it with bare hands.
What is the reason of this sound? Does thread is deformated a little bit while it is tightened and after it is released to normal position this sound appears?

awaiting your opinions

 

[kingnero]

I wouldn't say there is always a characteristic sound, nor that after that sound, the bolt or screw can be undone by hand.
In the clip you linked, I'd say the sound is due to the elastic deformation coming from the stress in the bolt. This deformation makes the male and female threads come into close contact, and having thus a high coefficient of friction. When you undo the bolt, you must first overcome this friction, and that makes that sound.

that's just my $.02

 

[drawoh]

cervantes,

I cannot view your video here at work.

Is it possible your screw was retained with thread-locker? These tend to make a clicking or popping sound when un-tightened.

--
JHG

 

[Compositepro]

I could not view the video either. The "click" you describe is usually due to stiction. When you turn the head of a bolt, and there is a distance between the head and the engaged thread, the bolt will elastically torque in this area before the the threads actually start to slide. When the thread breaks loose, the energy stored in the torqued bolt will release very suddenly and the threads shoot forward causing the bolt to ring. The longer the clamp length of the bolt, the more pronounced this effect, and the lower the frequency of the click.

 

[Tmoose]

I attribute the cause to extreme values of stick-slip ie stiction.
To quantify that I'd put a thin smear of anti-seize on the surface the fastener head seats against and repeat the un-screwing experiment.
Then the screw threads


As to the sound creation part, I think the large exposed wrench or screwdriver surfaces and the driver/fastener interfaces might bear a look.
For instance a large flywheel wrench, a wrench with plastic lined jaws or a brass wrench might change the resulting click.