chain saw

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An arborist using a chainsaw to fell a eucalyptus tree

A chainsaw (or chain saw) is a portable mechanical saw, powered by electricity, compressed air, hydraulic power, or most commonly a two-stroke engine.^[1] It is used in activities such as tree felling, limbing, bucking, pruning, by tree surgeons to fell trees and remove branches and foliage, to fell snags and assist in cutting firebreaks in wildland fire suppression, and to harvest firewood. Chainsaws with specially designed bar and chain combinations have been developed as tools for use in chainsaw art. Specialist chainsaws are used for cutting concrete.

Construction

Chainsaw chain

Media related to Chainsaw parts at Wikimedia Commons A chainsaw consists of several parts.

• Engine — almost always a two-stroke gasoline (petrol) internal combustion engine, usually with a cylinder volume of 30-120 cm³ or an electric motor.
• Drive mechanism — typically a centrifugal clutch and sprocket.
• Guide bar — an elongated bar with a round end of wear-resistant alloy steel typically 16 to 36 inches in length. An edge slot guides the cutting chain. Specialized loop-style bars, called bow bars, were also used at one time for bucking logs and clearing brush, although they are now rarely encountered due to increased hazards of operation.
• Cutting chain — Usually each segment in this chain (which is constructed from riveted metal sections similar to a bicycle chain, but without rollers) features small sharp cutting teeth. Each tooth takes the form of a folded tab of chromium plated steel with a sharp angular or curved corner and two cutting edges, one on the top plate and one on the side plate. Left-handed and right-handed teeth are alternated in the chain. Chains come in varying pitch and gauge; the pitch of a chain is defined as half of the length spanned by any three consecutive rivets (e.g., 0.325 inch), while the gauge is the thickness of drive link where it fits into the guide bar (e.g., 0.05 inch). Conventional "full complement" chain has one tooth for every two drive links. "Full skip" chain has one tooth for every three drive links. Built into each tooth is a depth gauge or "raker" which rides ahead of the tooth and limits the depth of cut, typically to around 0.025". Depth gauges are critical to safe chain operation. If left too high they will cause very slow cutting, if filed too low the chain will become more prone to kick back. Low depth gauges will also cause the saw to vibrate excessively. Excessive vibration is not only hard on the operator of the saw, but also the saw it's self.

The underside of each link features a small metal finger called a "drive link" which locates the chain on the bar, helps to carry lubricating oil around the bar, and engages with the engine's drive sprocket inside the body of the saw. The engine drives the chain around the track by a centrifugal clutch, engaging the chain under power, but allowing it to stop as the engine idles.

Dramatic improvements, chainsaw safety devices and overall design have taken place since the chainsaw's invention, saving many lives and preventing countless serious injuries. These include chainbrake systems, better chain design and anti-vibration systems. As chainsaw carving has become more popular, chainsaw manufacturers are making special short, narrow-tipped bars for carving. These are called "quarter tipped," "nickel tipped" or "dime tipped" bars, based on the size of the round tip. Echo sponsors a carving series,^[2] as well as carvers such as former Runaways singer Cherie Currie.^[3] RedMax specifically built the G3200 CV chainsaw for carving applications.^[4]

Maintenance

Logging near Apiary, Oregon

Most chainsaws require two sources of lubrication. Like most two-stroke engines, the engine is lubricated by its fuel, which contains about 2–5% oil (depending on the oil used) dissolved in the fuel. Separate chain oil or bar oil is used for the external lubrication of the bar and chain. The chain oil is depleted quickly because it tends to be thrown off the chain by centrifugal force, and it is soaked up by sawdust. The chain oil reservoir is usually filled up at the same time as refueling, and the reservoir is large enough so that the saw runs out of fuel and stops before the chain oil runs dry. Failing to keep the chain oil filled, or using an oil of incorrect viscosity, is a common source of damage to saws, and tends to lead to rapid wear of the bar, or the chain seizing or coming off the bar.

In addition to being quite thick, chain oil is particularly sticky (due to "tackifier" additives) to reduce the amount thrown off the chain. Although motor oil is a common emergency substitute, it is lost even faster and so leaves the chain under lubricated.

Chains must be kept sharp to perform well. They become blunt rapidly if they touch soil, metal or stones. When blunt, they tend to produce powdery sawdust, rather than the longer, clean shavings characteristic of a sharp chain; a sharp saw also needs very little force from the operator to push it into the cut. Special hardened chains (made with tungsten carbide) are used for applications where soil is likely to contaminate the cut, such as for cutting through roots.

The air intake filter tends to clog up with sawdust. This must be cleaned from time to time, but is not a problem during normal operation.

Safety

A chainsaw operator wearing full safety gear using a gasoline-driven chain saw

Despite safety features and protective clothing, injuries can still arise from chainsaw use, from the large forces involved in the work, from the fast-moving, sharp chain, or from the vibration and noise of the machinery.^[5]

A common accident arises from kickback, when a chain tooth at the tip of the guide bar catches on wood without cutting through it.^[6] This throws the bar (with its moving chain) in an upward arc toward the operator, often causing serious injury or even death.

Another dangerous situation occurs when heavy timber begins to fall or shift before a cut is complete — the chainsaw operator may be trapped or crushed. Similarly, timber falling in an unplanned direction may harm the operator or other workers, or an operator working at a height may fall or be injured by falling timber.

Like other hand-held machinery, the operation of chainsaws can cause vibration white finger,^[7] tinnitus or industrial deafness.

The risks associated with chainsaw use mean that protective clothing such as chainsaw boots, chainsaw trousers and hearing protectors are normally worn while operating them, and many jurisdictions require that operators be certified or licensed to work with chainsaws. Injury can also result if the chain breaks during operation due to poor maintenance or attempting to cut inappropriate materials.

Gasoline-powered chainsaws expose operators to harmful carbon monoxide (CO) gas, especially indoors or in partially enclosed outdoor areas.^[8]

Working techniques

Chainsaw training is designed to provide working technical knowledge and skills to safely operate the equipment.^[9]

• Sizeup - This is scouting and planning safe cuts, before starting the saw.

• Felling - The aim is for the tree to fall safely for limbing and cross cutting the log. It includes considerations for lean, bend, wind, branches, obstacles, snow load and tree damage. The goal is to avoid letting the tree fall on another tree or obstacle. After clearing the tree's base undergrowth for the retreat path and the felling direction; felling is properly done with three main cuts. To control the fall, the top and bottom cuts are made to form a wedged 45 degree hinge in the directional cut line. From the opposite side of the wedge, the felling cut is made horizontally and slightly above the bottom cut. When the hinge is properly set, the felling cut will begin the fall in the desired direction.^[10] A sitback is when a tree moves back opposite the intended direction. Placing a wedge in the felling cut can prevent a sitback from pinching the saw.

• Limbing - This is cutting the branches off the log. The operator must be able to properly reach the cut to avoid kickback.

• Bucking - This is cross cutting the felled log into sections. Setup is made to avoid binding the chainsaw within the changing log tensions and compressions. Safe bucking is started at the log highside and then sections worked offside, toward the butt end. The offside log falls and allows for gravity to help prevent binds. Watching the log's kerf movement while cutting, helps to indicate binds. Additional equipment (lifts, bars, wedges and winches) and special cutting techniques can help prevent binds.

• Binds - This is when the chainsaw is at risk or is stuck in the log compression. A log binded chainsaw is not safe, and must be carefully removed to prevent equipment damage.
  • Top bind — The tension area on log bottom, compression on top.
  • Bottom bind — The tension area on log top, compression on bottom.
  • Side bind — Sideways pressure exerted on log.
  • End bind — Weight compresses the log’s entire cross section.

• Brushing and Slashing - This is quickly clearing small trees and branches under 5 inches diameter. A hand piler may follow along to move out debris.

History

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Historical osteotome, a medical bone chainsaw

The prototype of the chain saw familiar today in the timber industry was pioneered in the late 18th Century by two Scottish doctors, John Aitken and James Jeffray, for symphysiotomy and excision of diseased bone respectively. The chain hand saw, a fine serrated link chain which cut on the concave side, was invented around 1783-1785. It was illustrated in Aitken's Principles of Midwifery or Puerperal Medicine (1785) and used by him in his dissecting room. Jeffray claimed to have conceived the idea of the chain saw independently about that time but it was 1790 before he was able to have it produced. In 1806, Jeffray published Cases of the Excision of Carious Joints by H. Park and P. F. Moreau with Observations by James Jeffray M.D.. In this communication he translated Moreau's paper of 1803. Park andMoreau described successful excision of diseased joints, particularly the knee and elbow. Jeffray explained that the chain saw would allow a smaller wound and protect the adjacent neurovascular bundle. While a heroic concept, symphysiotomy had too many complications for most obstetricians but Jeffray's ideas became accepted, especially after the development of anaesthetics. Mechanised versions of the chain saw were developed but in the later 19th Century, it was superseded in surgery by the Gigli twisted wire saw. For much of the 19th Century, however, the chain saw was a useful surgical instrument.

Electric chainsaw

The origin is debated, but a chainsaw-like tool was made around 1830 by the German orthopaedist Bernard Heine. This instrument, the osteotome, had links of a chain carrying small cutting teeth with the edges set at an angle; the chain was moved around a guiding blade by turning the handle of a sprocket wheel. As the name implies, this was used to cut bone.

Two important contributors to the modern chainsaw are Joseph Buford Cox and Andreas Stihl; the latter patented and developed an electrical chainsaw for use on bucking sites in 1926 and a gasoline-powered chainsaw in 1929, and founded a company to mass-produce them. In 1927, Emil Lerp, the founder of Dolmar, developed the world's first gasoline-powered chainsaw and mass-produced them.

McCulloch and Industrial Equipment Corporation in North America started to produce chainsaws. The early models were heavy, two-person devices with long bars. Often chainsaws were so heavy that they had wheels like dragsaws. Other outfits used driven lines from a wheeled power unit to drive the cutting bar.

After World War II, improvements in aluminum and engine design lightened chainsaws to the point where one person could carry them. In some areas the skidder (chainsaw) crews have been replaced by the feller buncher and harvester.

Chainsaws have almost entirely replaced simple man-powered saws in forestry. They come in many sizes, from small electric saws intended for home and garden use, to large "lumberjack" saws. Members of military engineer units are trained to use chainsaws.

Cutting stone, concrete and brick

A chainsaw cutting concrete. The hose supplies cooling water.

Special chainsaws are used to cut concrete, brick and natural stone. These use similar chains to ordinary chainsaws, but with cutting edges embedded with diamond grit. They may be gasoline or hydraulically driven, and the chain is lubricated with water, because of high friction and to remove stone-dust. The machine is used in construction, for example in cutting deep square holes in walls or floors, in stone sculpture for removing large chunks of stone during pre-carving, by fire departments for gaining access to buildings and in restoration of buildings and monuments, for removing parts with minimal damage to the surrounding structure.

Because the material to be cut is non-fibrous, there is much less chance of kickback. Therefore the most-used method of cutting is plunge-cutting, by pushing the tip of the blade into the material. With this method square cuts as small as the blade width can be achieved. Pushback can occur if a block shifts when nearly cut through, and pinches the blade, but overall the machine is less dangerous than a wood-cutting chainsaw.

See also

• Saw chain
• Chainsaws in popular culture
• Alaskan mill
• Bandsaw
• Circular saw
• Dragsaw
• Jigsaw
• Portable sawmill
• Small engine

References

• Chainsaw history

External Links

Wikimedia Commons has media related to: Chainsaws

• How a Chainsaw Works., Popular Science, August 1951: Article with good illustrations and cutaway of a basic chainsaw.