Sawing: Wikis


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Saw
Crosscut saw.JPG
A crosscut hand saw about 620 mm (24 inches) long
Classification Cutting
Types Hand saw
Back saw
Bow saw
Circular saw
Reciprocating saw
Band saw
Related Milling cutter

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.

Contents

Saw terminology

Diagram showing the teeth of a saw blade when looking front-on. The teeth protrude to the left and right, so that the saw cut (kerf) is wider than the blade width. The term set describes how much the teeth protrude.
  • Heel: The end closest to the handle.
  • Toe: The end farthest from the handle.
  • Front: The side with the teeth (the "bottom edge").
  • Back: Opposite the front ("top edge").
  • Teeth: Small sharp points along the cutting side of the saw.
  • Gullet: Valley between the points of the teeth
  • Fleam: The angle of the faces of the teeth relative to a line perpendicular to the face of the saw.
  • Rake: The angle of the front face of the tooth relative to a line perpendicular to the length of the saw. Teeth designed to cut with the grain (ripping) are generally steeper than teeth designed to cut across the grain (crosscutting)
  • Points per inch (25 mm): The most common measurement of the frequency of teeth on a saw blade. This is measured by setting the tip, or point, of one tooth at the zero point on a ruler, and then counting how many points are contained within one inch (25 mm) of length, counting inclusively. There will always be one more point per inch than there are teeth per inch (e.g., a saw with 14 points per inch will have 13 teeth per inch, a saw with 10 points per inch will have 9 teeth per inch). Some saws do not have the same number of teeth per inch throughout their entire length, but the vast majority do.
  • Teeth Per inch : Another common measurement of the amount of teeth residing in any one inch length of a saw blade. Usually abbreviated as TPI, eg a blade consisting of 18TPI (Teeth Per Inch).
  • Kerf: Width of the saw cut. On most saws the kerf is wider than the saw blade because the teeth are flared out sideways (set). This allows the blade to move through the cut easily without getting stuck (binding). However, some saws are made so that the teeth have no set on one side. This is done so that the saw can lie flat on a surface and cut along the surface without scratching it. These are referred to as flush cutting saws. Although the term kerf is often used to refer to the width of the saw blade, it actually means the width of the cut, which is affected by the width of the blade, the amount of wobble created during cutting, and the amount of material pulled out of the sides of the cut. This distinction can be important because the use of a blade that is too thin can result in excessive wobble and a wider kerf.

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 of the blade so that the cut width (kerf) is wider than the blade itself and the blade does not bind in the cut. The kerf of the blade is adjusted with a tool called a saw tooth setter.

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

History

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 bovid animals as a saw.

Handmade manufacture

Saws until at least the mid-19th century were made laboriously by hand. Teeth were punched out individually, then "set" by striking alternate teeth with a hammer against a "stake" or small anvil. Due to risk of breaking teeth, beginners were given saw set pliers which set even more slowly.[1]

Pit saw

In early English North America the pit saw was one of the principal industrial tools. It was (generally) operated over a pit across which the logs to be cut into boards were mounted. The saw was "a strong steel cutting-plate, of great breadth, with large teeth, highly polished and thoroughly wrought, some eight or ten feet in length" (Upham Hist. of Salem v1, p 191) with a handle on either end. The pit saw took at least 2 men to operate. One stood in the pit - the pitman, who was responsible for raising the saw on the backstroke - and the other was above - the sawyer, responsible for guiding the cut. The workers at a pit saw were some of the best paid in early colonial North America.

The pit saw is also known as a whipsaw.[2]

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.
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 dado blades. This first type is called a stacked dado blade. There is another type of dado blade capable of cutting variable width grooves. 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.

See also

References

  1. ^ Tomlinson, C., ed. (1866). Tomlinson's Cyclopaedia of Useful Arts. London: Virtue & Co.   Vol II, page 478.
  2. ^ Glossary of Tools

External links








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