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The screw is a mechanism that converts rotational motion to linear motion, and a torque (rotational force) to a linear force. [1] It is one of the six classical simple machines. The most common form consists of a cylindrical shaft with helical grooves or ridges called threads around the outside.
A screw axis.Mozzi–Chasles' theorem says that every Euclidean motion is a screw displacement along some screw axis.. In kinematics, Chasles' theorem, or Mozzi–Chasles' theorem, says that the most general rigid body displacement can be produced by a screw displacement.
A screw displacement (also screw operation or rotary translation) is the composition of a rotation by an angle φ about an axis (called the screw axis) with a translation by a distance d along this axis. A positive rotation direction usually means one that corresponds to the translation direction by the right-hand rule. This means that if the ...
The points in a body undergoing a constant twist motion trace helices in the fixed frame. If this screw motion has zero pitch then the trajectories trace circles, and the movement is a pure rotation. If the screw motion has infinite pitch then the trajectories are all straight lines in the same direction.
The very famous example is the joining of piston rod's extension with the connecting rod in the cross head assembly. Advantages: Quick assembly and disassembly is possible; It can take tensile as well as compressive force. Application: Joint between piston rod and cross head of a steam engine; Joint between valve rod and its steam
Theo Jansen's linkage. When the blue line at the right end of the picture is driven in a clockwise rotary motion, the leg (blue triangle at the bottom) executes a walking motion. Relative (dimensionless) proportions shown. Theo Jansen's kinetic sculpture Strandbeest. A wind-driven walking machine. A Strandbeest in action
To properly fasten or unfasten a screw, one applies the above rules: if a screw is right-handed, pointing one's right thumb in the direction of the hole and turning in the direction of the right hand's curled fingers (i.e. clockwise) will fasten the screw, while pointing away from the hole and turning in the new direction (i.e. counterclockwise ...
Lead is the distance along the screw's axis that is covered by one complete rotation of the screw thread (360°). Pitch is the distance from the crest of one thread to the next one at the same point. Because the vast majority of screw threadforms are single-start threadforms, their lead and pitch are the same. Single-start means that there is ...