What is “Screw”?
It is well known that it would be easier slide a heavy object on a slope rather than lifting it up streight when you move it to a higher location.
Moreover, it is easier for you to walk up on a moderate slope rather than a steep slope.
This means that heavy duty can be done with small force on a slope.
The vertical force to the slope is balanced with a reaction force which is the same as the object.The horizontal force to the slope pulls the object down on the slope.However, there is friction due to the small uneveness on the surface of of the slope so that the object can stop on a slope.
The angle of the slope gets narrower, the horizontal force to the slope gets smaller, however, the disctance to move the object gets proportionally longer.When you rush on a mountain path, you would choose a steep bybath rather than moderate main street.This would be the application of this slope idea in our daily life.
What we use this function of the slope is called a “Screw”.
When you look at the screw movement from the top, the screw is equivalent to a wedge wrapped around a cylinder.When a triangle paper is wrapped around a cylinder, the hypotenuse of the triangle draws a “Helix”.
Image of “Helix” of a Screw
The thread of the bolt is the groove formed along this “Helix”.
The groove part of the screw thread is called the root of the screw, and the protruding part is called the screw crest.The screws are usually used in combination with the nuts which has the grooves in a hole so that the crest and the root of the screws fit properly.
Shape of Screw
Moving an object along a slope corresponds to rotating the screw to make it engage with the female screw strongly.So, even if a slight force is applied in the direction to rotate the screw, a strong force would be appllied in the axial direction.
Various screws are standardized in JIS. However, not all of this is manufactured and in stock, and many are manufactured even if they are not in the standard. Tapping screws are a type of the screws that are often used in addition to the general screws (metric screw).