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The circular saw is a machine using a toothed metal cutting disc or blade. The term is also loosely used for the blade itself. The blade is a tool for cutting wood or other materials and may be hand-held or table-mounted. It can also be used to make narrow slots (dados). Most of these saws are designed with a blade to cut wood but may also be equipped with a blade designed to cut masonry, plastic, or metal. There are also purpose-made circular saws specially designed for particular materials. While today circular saws are almost exclusively powered by electricity, larger ones, such as those in sawmills, were traditionally powered by water turning a large wheel. A special arrangement involves the use of a hydraulic motor to propel the circular saw. This allows it to be fastened to heavy equipment, eliminating the need for a separate energy source.
Typically, the material to be cut is securely clamped or held in a vise, and the saw is advanced slowly across it. In variants such as the table saw, the saw is fixed and the material to be cut is slowly moved into the saw blade. As each tooth in the blade strikes the material, it makes a small chip. The teeth guide the chip out of the workpiece, preventing it from binding the blade.
- Cutting is by teeth on the edge of a thin blade
- The cut has narrow kerf and good surface finish
- Cuts are straight and relatively accurate
- The saw usually leaves burrs on the cut edge (which should then be addressed with sand paper)
- Saw setting should be done geometrically
Various claims have been made as to who invented the circular saw:
- A common claim is for a little-known sailmaker named Samuel Miller of Southampton, England who obtained a patent in 1777 for a saw windmill. However the specification for this only mentions the form of the saw incidentally, probably indicating that it was not his invention.
- Gervinus of Germany is often credited with inventing the circular saw in 1780
- Walter Taylor of Southampton had the blockmaking contract for Portsmouth Dockyard. In about 1762 he built a saw mill where he roughed out the blocks. This was replaced by another mill in 1781. Descriptions of his machinery there in the 1790s show that he had circular saws. Taylor patented two other improvements to blockmaking but not the circular saw. This suggests either that he did not invent it or that he published his invention without patenting it (which would mean it was no longer patentable).
- Another claim is that it originated in Holland in the sixteenth or seventeenth century. This may be correct, but nothing more precise is known.
- The use of a large circular saw in a saw mill is said to have been invented in 1813 by Tabitha Babbit, a Shaker spinster, who sought to ease the labour of the male sawyers in her community.
- The Barringer, Manners and Wallis factory in Rock Valley Mansfield, Nottinghamshire also claims to be the site of the invention.
Types of circular saw
In addition to hand-held circular saws (see below), different saws that use circular saw blades include:
- Miter saws (or Chop saw or Cut-off saw)
- Radial arm saws
- Saw mills
- Panel saws
- Biscuit joiners
- Pendulum saw or Swing saw
- Cold saws
- Flip Over Saws (the Combination of a Compound Miter and Table saw)
Originally, circular saws in mills had smaller blades and were used to resaw lumber after it passed through an "up and down" (muley or sash) saw leaving both vertical and circular saw marks on different sides of the same piece. These saws made it more efficient to cut small pieces such as lath. After 1813 or 1822 saw mills use large circular saws, up to nine feet (2.97 m) in diameter. Large saws demand more power than up-and-down saws and did not become practical for sawing timbers until they were powered by steam engines. They are either left or right-handed, depending on which side of the blade the plank falls away from. Benching determines which hand the saw is. Saws of this size typically have a shear pin hole, off axis, that breaks if the saw is overloaded and allows the saw to spin free. The most common version is the ITCO (insert tooth cut-off) which has replaceable teeth. Sawmill blades are also used as an alternative to a radial arm saw.
Cordwood saws, also called buzz saws in some locales, use blade of a similar size to sawmills. Where a sawmill rips (cuts with the grain) a cordwood saw crosscuts (cuts across the grain). Cordwood saws can have a blade from 20 to more than 36 inches (910 mm) diameter depending on the power source and intended purpose. Buzz saws are used to cut long logs (cordwood) and slabs (sawmill waste) into pieces suitable for home heating (firewood).
Most cordwood saws consist of a frame, blade, mandrel, cradle, and power source. The cradle is a tilting or sliding guide that holds logs during the cutting process. Some cordwood saws are run from a belt from a farm tractor power takeoff pulley. Others, mounted on a tractor's three-point hitch, connect to the rear power takeoff shaft. Self-powered models are equipped with small gasoline engines or even large electric motors as power sources. The mandrel is a shaft and set of bearings that support and transfer power to the blade. The frame is a structure that supports the cradle and blade at a convenient working height.
Cordwood saws were once very popular in rural America. They were used to cut smaller wood into firewood in an era when hand powered saws were the only other option. Logs too large for a cordwood saw were still cut by hand. Chainsaws  have largely replaced cordwood saws for firewood preparation today. Still, some commercial firewood processors and others use cordwood saws to save wear and tear on their chainsaws. Most people consider cordwood saws unsafe and outdated technology.
Hand-held circular saws
The term circular saw is most commonly used to refer to a hand-held electric circular saw designed for cutting wood, which may be used less optimally for cutting other materials with the exchange of specific blades. Circular saws can be either left or right-handed, depending on the side of the blade where the motor sits. A left-handed saw is typically easier to use if held in the right hand, and contrariwise for the right-handed saw, because the user does not need to lean across the saw to see the cutting line.
Blades for timber are almost universally tungsten carbide tipped (TCT). High speed steel (HSS) blades are also available. The saw base can be adjusted for depth of cut. Adjusting the depth of cut helps minimize kickback. The saw base can also be adjusted to tilt up to 50 degrees in relation to the blade.
The saw can be designed for the blade to mount directly to the motor's driveshaft (known colloquially as a sidewinder), or be driven indirectly by a perpendicularly-mounted motor via worm gears, garnering considerably higher torque (Worm-drive saws).
The worm-drive portable circular saw was invented in 1923 by Edmond Michel. In 1924 Michel formed a partnership with Joseph Sullivan, and together they started the Michel Electric Handsaw Company, with the sole purpose of manufacturing and marketing the saw invented by Michel. The company later renamed itself Skilsaw Inc., which today is a subsidiary of Robert Bosch GmbH. Portable circular saws are often still called Skilsaws or Skil saws. Its successor is still sold by Skil as the model 77. To get around the Skil patents, Art Emmons of Porter-Cable invented the direct-drive sidewinder saw in 1928. Recently smaller cordless circular saws with rechargeable batteries have become popular.
Cold saw(ing) machines are circular saws that are used in many metal cutting operations. The saw blades used are quite large in diameter and operate at low rotational speeds, and linear feeds. There are three common types of blades used in circular saws; solid-tooth, segmental tooth, and the carbide inserted-tooth. The circular saw is typically fed into the workpiece horizontally, and as the saw advances into the material, it severs the material by producing narrow slots. The material is usually held in place during the cutting operation by means of a vise. The chips produced by cutting are carried away from the material by both the teeth of the blade as well as the coolant or other cutting fluid used.
- Power saw
- Todd, Robert; Allen, Dell; Alting Leo (1994). Manufacturing Processes Reference Guide. Industrial Press. p. 28.
- English Patent Specification no. 1152 (1777); and see Inventors website
- Carolyn C. Cooper, "The Portsmouth System of Manufacture" Technology and Culture 25(2) (1984), 182–195; C. Singer et al., History of Technology IV (1958), 437; Norman Ball, 'Circular Saws and the History of Technology' Bulletin of the Association for Preservation Technology Vol. 7, No. 3. (1975), pp. 79–89.
- Ball, 'Circular Saws' quoting M. Powis Bale, Woodworking Machinery. Its Rise, Progress and Construction.
- John O. Curtis, "The Introduction of the Circular Saw in the Early 19th Century". Bulletin of the Association for Preservation Technology Vol. 5, No. 2 (1973), pp. 162–189; also Inventors website and Wood News
- Chainsaws - Chainsaw History
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