Saw: Difference between revisions

Saw
	A crosscut hand saw about 620 mm long
Classification	Cutting
Types	Hand saw; Back saw; Bow saw; Circular saw; Reciprocating saw; Band saw
Related	Milling cutter

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Revision as of 23:05, 23 February 2009

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A saw is a tool that uses a hard blade or wire with an abrasive edge to cut through softer materials. The cutting edge of a saw is either a serrated blade or an abrasive. A saw may be worked by hand, or powered by steam, water, electric or other power.

In a modern serrated saw, each tooth is bent to a precise angle called its "set". The set of the teeth is determined by the kind of cut the saw is intended to make. For example, a "rip saw" has a tooth set that is similar to the angle used on a chisel. The idea is to have the teeth rip or tear the material apart. Some teeth are usually splayed slightly to each side the blade, so that the cut width (kerf) is wider than the blade itself and the blade does not bind in the cut.

An abrasive saw uses an abrasive disc or band for cutting, rather than a serrated blade.

According to Chinese tradition, the saw was invented by Lu Ban. In Greek mythology, Talos, the nephew of Daedalos, invented the saw. In fact, saws date back to prehistory, and likely evolved from Neolithic tools or bone tools. The early ancestors of man, in the Pleistocene era, likely first used a jaw bone of 5 bovid animals as a saw.

Types of saw blades and the cuts they make

Blade teeth are of two general types: Tool steel or carbide. Carbide is harder and holds a sharp edge much longer.

Band Saw Blade: A straight blade welded into a circle. Used mainly at sawmills & steel service centers. Preferred over circular saws due to less waste.

A Band Saw Blade used at a steel service center

A Band Saw Blade used at a steel service center
A Band Saw Blade used at a sawmill

A Band Saw Blade used at a sawmill

Crosscut: In woodworking, a cut made at (or near) a right angle to the direction of the grain of the workpiece. A crosscut saw is used to make this type of cut.
Rip cut: In woodworking, a cut made parallel to the direction of the grain of the workpiece. A rip saw is used to make this type of cut.
Plytooth: A circular saw blade with many small teeth designed for cutting plywood with minimal splintering.
Dado blade: A special type of circular saw blade used for making wide grooved cuts in wood so the edge of another piece of wood will fit into the groove to make a joint. Dado blades can make different width grooves by addition or removal of chipper blades of various widths between the outer sadaio blades. This first type is called a stacked dado blade. There is another type of dado blade capable of cutting variable width groove. Das. An adjustable dado utilizes a movable locking cam mechanism which causes the blade to wobble sideways more or less. This allows continuously variable groove width from the lower to upper design limits of the dado.

Materials used for saws

There are several materials used in saws, with each of its own specifications.

Brass: Mostly used in back saws because of its low price, its flow characteristics that make the material relatively easy to cast, and unlike other types of saw, the forces that take place in back saws are relatively low because of the pulling motion used.
Steel: Used in almost every existing kind of saw. Because steel is cheap, easy to shape, and very strong, it has the right properties for most kind of saws.
Diamond: Used only in saws for the really heavy cutting. It is very expensive and comes in two shapes: ropes and circular saws. Mostly used for cutting concrete and other materials with rock-like structures or in softer materials, such as wood, where the precision and high volume of work justifies the expense of diamond-edged cutting tools. Diamond saws are made by combining powder metal with diamond crystals, which are then heated and pressed into a molding to form the diamond segments.

Uses

Saws are most commonly used for cutting hard materials. They are used extensively in forestry, construction, demolition, medicine, and hunting.
Some saws are used as instruments to make music.
Chainsaw carving is a flourishing modern art form. Special saws have been developed for this purpose.

Saws in nature

Teeth or similar mouthparts are used by many creatures to cut their food.
Sawgrass is an example of a plant that use serrated leaves as a defense mechanism.
The sawfish has a sawlike snout that is, however, not used as a saw.