Saw
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, electricity or other power.
Terminology
- 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, e.g. 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
In ancient Egypt, saws made of copper are documented as early as the Early Dynastic Period, circa 3,000–2,800.[1] Examples of saws and models of saws have been found in many contexts throughout Egyptian history. Particularly useful are tomb wall illustrations of carpenters at work that show sizes and the use of different types. Egyptian saws were set with the teeth projecting only on one side, rather than in the modern fashion with the more advantageous alternating set.
According to Chinese tradition, the saw was invented by Lu Ban.[2] In Greek mythology, as recounted by Ovid,[3] Talos, the nephew of Daedalus, invented the saw. In archeological reality, saws date back to prehistory and most probably evolved from Neolithic stone or bone tools. "[T]he identities of the ax, adz, chisel, and saw were clearly established more than 4,000 years ago."[4]
Handmade manufacture
Until at least the mid-19th century, saws were made laboriously by hand. Teeth were filed 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.[5]
Saw pits
Main articles:
Saw pit and
Two-man sawIn early English North America, the pit saw was one of the principal industrial tools. It was a two-man saw, 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"[6] with a handle on either end. The pit saw took at least two men to operate. The "pitman" stood in the pit— to raise the saw for the backstroke—and the "sawyer", standing above, guided the cut. Pit-saw workers were among the best paid in early colonial North America.
The pit saw is also known as a whipsaw.[7]
Types of saws
Hand saws
Hand saw uses the blades thickness to remain stiff. The pull stroke also reduces the amount of stiffness required. Some examples are:
- Crosscut saw for making cuts perpendicular to the grain
- Rip saw for cutting along the grain
- Two-man saw for cutting large logs or trees
- Plywood saw fine-toothed blade to reduce tearing of plywood
- Veneer saw two edged saw with fine teeth used to cut veneer
- Hacksaw fine-toothed tempered blade under tension for cutting metal, bone, and other hard materials.
- Pad saw, keyhole saw, jab saw narrow bladed saw.
- Fret saw for cutting intricate wood patterns
Back saws
Main articles:
Backsaw and
Japanese sawThe second category of hand saws utilize a thinner blade by reinforcing it with a steel or brass back. Back saws are differentiated by the length of the blade. Some examples are:
- Miter saw used to make accurate crosscuts and miters in a workpiece
- Tenon saw also called a Dovetail saw or sash saw is used in woodworking for precise work
Mechanically powered saws
Circular blade saws
- Circular saw, used in industrial sawing of log and beams, typically found in sawmills – also name given to smaller hand-held saws
- Table saw, circular blade rising through a slot in a table. A smaller direct-drive versions can be set on a workbench is called workbench saw. If set on steel legs it is called a Contractor's Saw. A heavier version, which is more precise and more powerful and driven by multiple belts with an enclosed base stand is called a Cabinet saw. A new version, called a hybrid saw, has the lighter weight mechanism of a Contractor saw but with an enclosed base like the Cabinet saw.
- Radial arm saw is a versatile machine used mainly for cross-cutting. The blade is pulled on a guide arm through a piece of wood held stationary on the saw's table
- Rotary saw is used to make accurate cuts without the need for a pilot hole in wallboard, plywood, and other thin materials. It can be called a spiral cut saw or a "RotoZip".
- Electric miter saw, (also called chop saw, cut-off saw or power miter box) is used for making accurate cross cuts and miter cuts. The basic model has its circular blade fixed at a 90° angle to the vertical, a compound miter saw's blade can be adjusted to other angles. A sliding compound miter saw has a blade which can be pulled through the work similar to the action of a radial arm saw, which gives a greater capacity for cutting wider workpieces.
- Concrete saw, usually powered by an internal combustion engine and used with a Diamond Blade to cut concrete or asphalt pavement.
- Abrasive saw, which uses an abrasive disc for cutting rather than a toothed blade. Abrasive saws are used for cutting very hard materials, such as metal.
Reciprocating blade saws
- Jigsaw or saber saw (US) has a narrow blade for cutting irregular shapes. The term jigsaw was also commonly used for what is now called a scroll saw.
- Reciprocating saw or sabre saw (UK and Australia) use an action similar to a jigsaw. They are larger, more powerful and use a longer stroke with the blade parallel to the barrel. It is useful for demolition work or for cutting pipe, and is sometimes powered by compressed air.
- Scroll saw is a saw for making intricate curved cuts (scrolls).
- Dragsaw is used for bucking logs before the advent of the chainsaw.
- Sternal saw is used in surgery to open a patient's sternum.
Continuous band
Types of blades
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 long band with teeth on one side welded into a circle. Less waste than circular saws due to blade being thinner. More heat disapation because there is more blade to do the cutting. Usually run at a slower speed than circular saw.
- Crosscut
- In woodworking, a cut made at (or near) a right angle to the direction of the wood 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.
- Strob Saw Blade
- A circular saw blade with special rakers/cutters to easily saw through green or uncured wood which would otherwise jam the saw blade.
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
- Fixed onto the saw blade's base to form diamond saw blades. As diamond is a superhard material, diamond saw blades can be used to cut hard and brittle, or abrasive materials, for example, stone, concrete, asphalt, bricks, ceramics, glass, semiconductor and gem stone. There are many methods to fix the diamonds onto the blades' base and there are various diamond saw blades, which are used in a variety of fields.[8]
- High speed steel (HSS)
- The whole saw blade is made of High Speed Steel (HSS). HSS saw blades are mainly used to cut steel, copper, aluminum and other metal materials. If high-strength steels (e.g., stainless steel) are to be cut, the blades made of cobalt HSS (e.g. M35, M42) should be used.[8]
- Tungsten carbide
- Normally, there are two ways to use tungsten carbide to make saw blades:[8]
- Carbide tipped saw blades: The saw blade's teeth are tipped (via welding) with small pieces of sharp tungsten carbide block. This type of blade is also called TCT (Tungsten Carbide Tipped) saw blade. Carbide tipped saw blades are widely used to cut wood, plywood, laminated board, plastic, grass, aluminum and some other metals.
- Solid carbide saw blades: The whole saw blade is made of tungsten carbide. Comparing with HSS saw blades, solid carbide saw blades have higher hardness under high temperatures, and are more durable, but they also have a lower toughness.
Uses
- Saws are most commonly used for cutting hard materials. They are used extensively in forestry, construction, demolition, medicine, and hunting.
- Musical saws are used as instruments to make music.
- Chainsaw carving is a flourishing modern art form. Special saws have been developed for this purpose.
- The production of Lumber, lengths of squared wood for use in construction, begins with the felling of trees and the transportation of the logs to a sawmill.
Plainsawing: Lumber for structural uses is typically plainsawn (also called flatsawn), a method of dividing the log that produces the maximum yield of useful pieces and therefore the greatest economy.
Quarter sawing: This sawing method produce edge-grain or vertical gain lumber, in which annual growth rings run more consistently perpendicular to the pieces' wider faces.
See also
References
- ^ Walter B. Emery Excavations at Saqqara, The Tomb of Hemaka and Hor-Aha, Cairo, Government Press, Bulâq, 1938 (2 vols)
- ^ Lu Ban and The Invention of the Saw History Anecdote at Cultural China website
- ^ Ovid Metamorphoses Bk VIII:236-259: The death of Talos A. S. Kline translation, Electronic Text Center at University of Virginia Library
- ^ Richard S. Hartenberg, Joseph A. McGeough Neolithic Hand Tools at Encyclopaedia Britannica Online
- ^ Tomlinson, C., ed. (1866). Tomlinson's Cyclopaedia of Useful Arts. London: Virtue & Co. Vol II, page 478.
- ^ Charles W. Upham Salem Witchcraft with an account of Salem Village and a History of Opinions on Witchcraft and Kindred Subjects. Frederick Unger, New York, 1978 (Reprint), 2 vols., vol. 1, p 191
- ^ Glossary of Tools at (American) Pilgrim Hall Museum website
- ^ a b c Types of Saw Blades
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