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- William Sellers
- Related Topics:
- lag screw
- screw thread
- wood screw
- cap screw
- power screw
screw
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What is a screw in machines?
A screw in machine construction is typically a circular cylindrical component featuring a continuous helical rib. It serves two primary functions: fastening and modifying force and motion.
As a fastener, machine screws clamp parts together, often used with a nut or when a part has a threaded hole. When tightened, these screws stretch, creating a tensile load that secures the components. Setscrews, another type, fit into a threaded hole, pressing into a mating member to prevent movement.
As a force and motion modifier, screws, known as power screws, convert torque to thrust. For example, a screwjack uses a turning screw in a stationary nut to generate thrust, often for lifting heavy objects.
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What are the main parts of a screw?
A screw typically consists of a cylindrical body with a helical rib, known as the screw thread, which wraps around it. The screwhead is the part of the screw that is usually rotated to drive it into a material. Screws can act as fasteners or to modify force and motion.
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How does a screw work to hold things together?
A screw, typically a cylindrical component featuring a continuous helical rib, serves as a fastener by clamping machine parts together, either using a threaded hole or alongside a nut. When tightened, these screws stretch, generating a tensile load that firmly holds the parts in place. Self-tapping screws are able to form or cut threads in materials like metal and plastic as they're driven into prepared holes. Wood screws come in various sizes, and larger ones may require pilot holes to prevent the wood from splitting.
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What are common types of screws used in machines?
Screws serve as fasteners or to modify force and motion in machines.
Common types of screws include:
* Machine screws Clamp machine parts with a threaded hole or nut, stretching when tightened.
* Setscrews Fit into a threaded hole, pressing into a mating member to prevent motion.
* Studs Rods threaded on both ends, screwed into one member and clamped with a nut.
* Self-tapping screws Form or cut threads in materials like metal, plastic, or wood when screwed into cored holes.
* Wood screws Used for wood, with pilot holes to prevent splitting.
* Lag screws Large wood screws fasten heavy objects to wood.
* Power screws Modify force and motion, like in a screwjack that converts torque to thrust.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Why do screws have different shapes and thread patterns?
Screws come in different shapes and thread patterns to serve various functions. Cap and machine screws are designed to clamp machine parts, stretching when tightened to hold the parts together. Setscrews fit into threaded holes, pressing into a mating member to prevent motion. Self-tapping screws form or cut threads when driven into materials like metal or plastic.
Wood screws come in various sizes, with pilot holes sometimes needed to prevent splitting, while lag screws are large wood screws for fastening heavy objects to wood. Power screws modify force and motion, such as a screwjack that converts torque to thrust for lifting heavy objects. Special screws with cross-shaped slots require screwdrivers with tips that fit the slots.
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How does using the right screw affect how a machine works or stays safe?
Screws serve as fasteners and force/motion modifiers in machines. Cap and machine screws clamp parts together, using tensile load to enhance stability. Setscrews prevent movement between components. Self-tapping screws create threads in materials like metal and plastic, ensuring a secure fit.
Power screws, like those in a screwjack, convert torque to thrust, enabling heavy lifting. Workpiece tables in machine tools use screws for linear motion. Selecting the correct screw type is crucial for maintaining the machine's functionality and safety by ensuring proper clamping force, preventing slippage, and facilitating controlled movement.
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screw, in machine construction, a usually circular cylindrical member with a continuous helical rib, used either as a fastener or as a force and motion modifier.
Although the Pythagorean philosopher Archytas of Tarentum (5th century bc) is the alleged inventor of the screw, the exact date of its first appearance as a useful mechanical device is obscure. Though invention of the water screw is usually ascribed to Archimedes (3rd century bc), evidence exists of a similar device used for irrigation in Egypt at an earlier date. The screw press, probably invented in Greece in the 1st or 2nd century bc, has been used since the days of the Roman Empire for pressing clothes. In the 1st century ad, wooden screws were used in wine and olive-oil presses, and cutters (taps) for cutting internal threads were in use.
In the , which shows the main types of screws and screwheads in modern use, the cap and machine screws are used to clamp machine parts together, either when one of the parts has a threaded hole or in conjunction with a nut. These screws stretch when tightened, and the tensile load created clamps the parts together. Machine screws have various types of heads, most with screwdriver slots. They are made in smaller sizes than cap screws and bolts.
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The setscrew in the fits into a threaded hole in one member; when tightened, the cup-shaped point is pressed into a mating member (usually a shaft) and prevents relative motion. Setscrews are also made with conical and cylindrical points that fit in matching holes and with slotted and square heads.
A stud is a rod threaded on both ends. It is permanently screwed into one member and clamped by means of a nut on the other end.
Self-tapping screws form or cut mating threads in such materials as metals, plastics, glass fibre, asbestos, and resin-impregnated plywood when driven or screwed into drilled or cored (cast) holes. The self-tapping screw in the forms threads by displacing material adjacent to a pilot hole so that it flows around the screw. Thread-cutting tapping screws have cutting edges and chip cavities that produce a mating thread by removing material.
Wood screws are made in a wide variety of diameters and lengths; when using the larger sizes, pilot holes are drilled to avoid splitting the wood. Lag screws are large wood screws used to fasten heavy objects to wood. Heads are either square or hexagonal.
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Screws that modify force and motion are known as power screws. A screwjack converts torque (turning moment) to thrust. The thrust (usually to lift a heavy object) is created by turning the screw in a stationary nut. By using a long bar to turn the screw, a small force at the end of the bar can create a large thrust force. Workpiece tables on machine tools are moved linearly on guiding ways by screws that rotate in bearings at the ends of the tables and mate with nuts fixed to the machine frame. A similar torque-to-thrust conversion can be obtained by either rotating an axially fixed screw to drive a rotationally fixed nut along the screw or by rotating an axially fixed nut to drive a rotationally fixed screw through the nut.