History of the Screw
A complete history of the screw is not available. There is historical evidence that by the first century it was used in a screw press. But screw presses used by the Romans to squeeze olives for oil and grapes for wine have been found. Archytas of Tarrentum is credited by the Greeks with the invention of the first screw. However, Archimedes the Greek philosopher is also credited with inventing the screw around 234 BC. The Archimedes screw was used in a water pump that employs a rotating helical chamber to cause water to move uphill. However, records concerning the history of the screw show that screws were used as early as ancient Greek and Egyptian times.
Screw Cutting Lathes
They were used only in a few machines as screws had to be laboriously cut by hand. Screw cutting lathes were not invented until the 15th century and therefore screws became more widely available. For example, they were used in clocks and other items.
Classical Simple Machines
The screw is one of the six classical simple machines.1 It a mechanism that changes rotational motion to linear motion and rotational force or torque to a linear force. A screw when is a narrow incline plane wrapped around a cylinder. It consists of a cylindrical shaft with helical grooves or ridges around the outside called threads. The screw was the last of the six simple machines to be developed. Galileo Galilei is credited with explaining the complete dynamic theory of all six simple machines including the screw in 1600. LE MECCANICHE or ON MECHANICS (1600) described his work on these subjects..
A screw is a helix. The word helix comes from the Greek word for “twisted curve.” A helix is a curve in three-dimensional space such as coil springs or the handrail of spiral staircase. Helices are either right-handed or left-handed and are defined by how the screw motion operates. A helix is right-handed if a clockwise screwing motion moves the helix away from an observer. However, if it moves towards the observer, it is called a left-handed helix. Handedness is also known as chirality. Most screws are right-hand helices and the pitch of a screw is the height of one complete helix turn. It is measured parallel to the axis of the helix.
Helices come in several varieties. A spiral on a conic surface is a conic helix. A circular helix has constant hand curvature and constant torsion. A general or cylindrical helix is a curve if the ratio of curvature to torsion is constant. And a curve is called a slant helix if its principal normal makes a constant angle with a fixed line in space. Famously, a DNA molecule is described as two intertwined helices or a double helix. A double helix consists of two typically congruent helices with the same axis.
No history of the screw would be complete without discussing tendril perversions. These are man-made as well as occuring naturally in nature.Some curves in nature are constructed of multiple helices of different handedness joined together by transitions called tendril perversions. Many climbing plants such as pea plants or morning glories exhibited tendril perversions. The cord of a land line phone is another example.
Like other simple machines, a screw can amplify force. The smaller the pitch or the distance between the screw threads the greater the mechanical advantage. The mechanical advantage is the ratio of output to input force. But not all screws have threads. The history of the screw would not be complete without mentioning that a cork screw is also a screw. A corkscrew is a helix-shaped rod with a sharp point but no threads
Craftech Industries offers a wide variety of screws ranging in size, style of head, driver point type, length, material, and characteristics of the thread. We also do custom drive styles. To learn more about our capabilities, please call us at 800-833-5130 or e-mail @ [email protected] craftechind.co.
1The other five are the incline plane, wheel and axle, wedge, pulley and lever.