Brief description

A screw is a simple machine consisting of an inclined plane wrapped around a cylinder or cone. It is primarily used to hold objects together or to lift materials.

Use / Function

Fastening: Joining two or more objects together securely (e.g., wood screws, bolts).
Motion Conversion: Converting rotational motion into linear motion (e.g., lead screws in machinery).
Lifting: Raising water or granular materials (e.g., Archimedes’ screw).
Pressing: Applying great force for squeezing or crushing (e.g., wine press, printing press).
Scale: From tiny watch components to massive industrial presses.

Operating Principle

The screw works by converting torque (rotational force) into linear force. The distance between the threads is called the “pitch.”

Mechanical Advantage: A small rotational force applied over a long distance (the circumference of the turn) creates a large axial force over a short distance (the pitch).
Self-locking: In many screw designs, friction prevents the screw from turning back under load, keeping it secure.

How to create it

Preparation: Select a cylindrical rod of wood or metal.
Marking: Draw a diagonal line around the cylinder to define the thread path (helix).
Cutting:
- Wood: Carve out the material between the marked lines to create the thread profile.
- Metal: Use a file or a harder cutting tool (die) to cut the threads.
Matching: Create a corresponding internal thread (nut) by tapping a hole or carving the inside of a hollow cylinder.

Materials needed

Rod: Hardwood (oak, hickory) or metal (bronze, iron, steel).
Cutting Tools: Chisels, files, or harder metal cutters.
Lubricant: Tallow or oil to ease the cutting and movement.

Variants and improvements

Archimedes’ Screw: A large screw inside a pipe used for lifting water.
Wood Screw: Tapered point for penetrating wood.
Machine Screw/Bolt: Uniform cylinder for use with a nut.
Ball Screw: Uses ball bearings for low friction (modern high-precision).

Limits and risks

Stripping: Applying too much torque can shear off the threads, rendering the screw useless.
Friction: A significant amount of input energy is lost to friction.
Corrosion: Metal screws can rust and seize, making them impossible to remove.