Jackhammer

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Drilling a blast hole with a jackhammer Tennessee Valley Authority Douglas Dam French Broad River Sevier County TN man with jackhammer 1942.gif
Drilling a blast hole with a jackhammer
(video) A construction worker uses a jackhammer in Japan.

A jackhammer (pneumatic drill or demolition hammer in British English) is a pneumatic or electro-mechanical tool that combines a hammer directly with a chisel. It was invented by William Mcreavy, who then sold the patent to Charles Brady King. [1] Hand-held jackhammers are generally powered by compressed air, but some are also powered by electric motors. Larger jackhammers, such as rig mounted hammers used on construction machinery, are usually hydraulically powered. They are typically used to break up rock, pavement, and concrete.

British English is the standard dialect of English language as spoken and written in the United Kingdom. Variations exist in formal, written English in the United Kingdom. For example, the adjective wee is almost exclusively used in parts of Scotland and Ireland, and occasionally Yorkshire, whereas little is predominant elsewhere. Nevertheless, there is a meaningful degree of uniformity in written English within the United Kingdom, and this could be described by the term British English. The forms of spoken English, however, vary considerably more than in most other areas of the world where English is spoken, so a uniform concept of British English is more difficult to apply to the spoken language. According to Tom McArthur in the Oxford Guide to World English, British English shares "all the ambiguities and tensions in the word 'British' and as a result can be used and interpreted in two ways, more broadly or more narrowly, within a range of blurring and ambiguity".

A pneumatic tool, air tool, air-powered tool or pneumatic-powered tool is a type of power tool, driven by compressed air supplied by an air compressor. Pneumatic tools can also be driven by compressed carbon dioxide (CO2) stored in small cylinders allowing for portability.

Hammer tool

A modern day hammer is a tool consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nails into wood, to shape metal, or to crush rock. Hammers are used for a wide range of driving, shaping, and breaking applications.

Contents

A jackhammer operates by driving an internal hammer up and down. The hammer is first driven down to strike the back and then back up to return the hammer to the original position to repeat the cycle. The effectiveness of the jackhammer is dependent on how much force is applied to the tool. It is generally used like a hammer to break the hard surface or rock in construction works and it is not considered under earth moving equipment, along with its accessories (i.e., pusher leg, lubricator).

In British English, electromechanical versions are colloquially known as "Kangos".

History

The first steam-powered drill was patented by Samuel Miller in 1806. This drill used steam only for raising the drill. [2] Pneumatic drills were developed in response to the needs of mining, quarrying, excavating, and tunneling. A pneumatic drill was proposed by a C. Brunton in 1844. [3] [4] In 1846 a percussion drill that could be worked by steam or atmospheric pressure obtained from a vacuum was patented in Britain by Thomas Clarke, Mark Freeman and John Varley. [5] The first American "percussion drill" was made in 1848 and patented in 1849 by Jonathan J. Couch of Philadelphia, Pennsylvania. [6] In this drill, the drill bit passed through the piston of a steam engine. The piston snagged the drill bit and hurled it against the rock face. It was an experimental model. In 1849, Couch's assistant, Joseph W. Fowle, filed a patent caveat for a percussion drill of his own design. In Fowle's drill, the drill bit was connected directly to the piston in the steam cylinder; specifically, the drill bit was connected to the piston's crosshead. The drill also had a mechanism for turning the drill bit around its axis between strokes and for advancing the drill as the hole deepened. [7] By 1850 or 1851, Fowle was using compressed air to drive his drill, making it the first true pneumatic drill. [8]

A patent caveat, often shortened to caveat, was a legal document filed with the United States Patent Office. Caveats were instituted by the U.S. Patent Act of 1836, but were discontinued in 1909, with the U.S. Congress abolishing the system formally in 1910. A caveat was similar to a patent application with a description of an invention and drawings, but without examination for patentable subject matter and without a requirement for patent claims. A patent caveat was an official notice of intention to file a patent application at a later date. A caveat expired after one year, but could be renewed by paying an annual fee of $10.

Crosshead

A crosshead is a mechanism used as part of the slider-crank linkages of long reciprocating engines and reciprocating compressors to eliminate sideways pressure on the piston. Also, the crosshead enables the connecting rod to freely move outside the cylinder. Because of the very small bore-to-stroke ratio on such engines, the connecting rod would hit the cylinder walls and block the engine from rotating if the piston was attached directly to the connecting rod like on trunk engines. Therefore, the longitudinal dimension of the crosshead must be matched to the stroke of the engine.

The demand for pneumatic drills was driven especially by miners and tunnelers, because steam engines needed fires to operate and the ventilation in mines and tunnels was inadequate to vent the fires' fumes; there was also no way to convey steam over long distances, e.g., from the surface to the bottom of a mine; and mines and tunnels occasionally contained flammable explosive gases such as methane. By contrast, compressed air could be conveyed over long distances without loss of its energy, and after the compressed air had been used to power equipment, it could ventilate a mine or tunnel.

Methane simplest organic molecule with one carbon atom and four hydrogen

Methane (or ) is a chemical compound with the chemical formula CH4 (one atom of carbon and four atoms of hydrogen). It is a group-14 hydride and the simplest alkane, and is the main constituent of natural gas. The relative abundance of methane on Earth makes it an attractive fuel, although capturing and storing it poses challenges due to its gaseous state under normal conditions for temperature and pressure.

In Europe since the late 1840s, the king of Sardinia, Carlo Alberto, had been contemplating the excavation of a 12-kilometer (7.5 mi) tunnel through Mount Fréjus to create a rail link between Italy and France, which would cross his realm. [9] [10] The need for a mechanical rock drill was obvious and this sparked research on pneumatic rock drills in Europe. A Frenchman, Cavé, designed, and in 1851 patented, a rock drill that used compressed air; but the air had to be admitted manually to the cylinder during each stroke, so it was not successful. [11] In 1854, in England, Thomas Bartlett made and then patented (1855) a rock drill whose drill bit was connected directly to the piston of a steam engine. In 1855 Bartlett demonstrated his drill, powered by compressed air, to officials of the Mount Fréjus tunnel project. [12] (In 1855, a German, Schumann, invented a similar pneumatic rock drill in Freiburg, Germany. [13] ) Bartlett’s drill was refined by the Savoy-born engineer Germain Sommeiller (1815-1871) and his colleagues, Grandis and Grattoni, by 1861. [14] Thereafter, many inventors refined the pneumatic drill. [15] Sommeiller took his drill to the lengthy Gotthard Pass Tunnel then being built to link railways between Switzerland and Italy under the Alps. Atlas Copco and Ingersoll Rand were two important drill companies in Europe and America respectively, each holding patents and dominating the industry. From this mining and railway tunnelling expanded.

Kingdom of Sardinia former Italian state (1324–1861)

The Kingdom of Sardinia was a state in Southern Europe from the early 14th until the mid-19th century.

Charles Albert of Sardinia King of Sardinia

Charles Albert was the King of Sardinia from 27 April 1831 to 23 March 1849. His name is bound up with the first Italian constitution, the Albertine Statute, and with the First Italian War of Independence (1848–1849).

The Fréjus Rail Tunnel is a rail tunnel of 13.7 km (8.5 mi) length in the European Alps, carrying the Turin–Modane railway through Mont Cenis to an end-on connection with the Culoz–Modane railway and linking Bardonecchia in Italy to Modane in France. Its mean altitude is 1,123 m and it passes beneath the Pointe du Fréjus and the Col du Fréjus.

Terminology

The word "jackhammer" is used in North American English and Australia, while "pneumatic drill" is used colloquially elsewhere in the English speaking world, although strictly speaking a "pneumatic drill" refers to a pneumatically driven jackhammer. [16]

North American English is the most generalized variety of the English language as spoken in the United States and Canada. Because of their related histories and cultures and the similarities between the pronunciation, vocabulary, and accent of American English and Canadian English, the two spoken varieties are often grouped together under a single category. Due to historical and cultural factors, Canadian English and American English retain numerous distinctions from each other, with the differences being most noticeable in the two languages' written forms. Canadian spellings are primarily based on British usage as a result of Canada's longer-standing connections with the United Kingdom. Canadians are generally tolerant of both British and American spellings, with British spellings being favored in more formal settings and in Canadian print media. Spellings in American English have been highly influenced by lexicographers like Noah Webster, who sought to create a standardized form of English that was independent of British English. Despite these differences, the dialects of both Canada and the United States are similar. The United Empire Loyalists who fled the American Revolution (1765–1783) have had a large influence on Canadian English from its early roots.

Australia Country in Oceania

Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. It is the largest country in Oceania and the world's sixth-largest country by total area. The neighbouring countries are Papua New Guinea, Indonesia, and East Timor to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. The population of 25 million is highly urbanised and heavily concentrated on the eastern seaboard. Australia's capital is Canberra, and its largest city is Sydney. The country's other major metropolitan areas are Melbourne, Brisbane, Perth, and Adelaide.

In Britain, electromechanical versions are colloquially known as "Kangos". [17] The term comes from the former British brand name now owned by Milwaukee tools.

United Kingdom Country in Europe

The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a sovereign country located off the north-western coast of the European mainland. The United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland, and many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state, the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to the east, the English Channel to the south and the Celtic Sea to the south-west, giving it the 12th-longest coastline in the world. The Irish Sea lies between Great Britain and Ireland. The UK's 242,500 square kilometres (93,600 sq mi) were home to an estimated 66.0 million inhabitants in 2017.

Use

A Wacker Neuson gasoline-powered breaker on a demolition site BH E02 web.jpg
A Wacker Neuson gasoline-powered breaker on a demolition site

A full-sized portable jackhammer is impractical for use against walls and steep slopes, except by a very strong person, as the user would have to both support the weight of the tool, and push the tool back against the work after each blow. A technique developed by experienced workers is a two-man team to overcome this obstacle of gravity: one operates the hammer and the second assists by holding the hammer either on his shoulders or cradled in his arms. Both use their combined weight to push the bit into the workface. This method is commonly referred to as horizontal jackhammering.

Another method is overhead jackhammering, requiring strength conditioning and endurance to hold a smaller jackhammer, called a rivet buster, over one's head. To make overhead work safer a platform can be used. One such platform is a P.A.M. (Positioner Actuator Manipulator). This unit takes all the weight and vibration from the user.

Types

Pneumatic

A compressor for running a pneumatic jackhammer. Aa pneumatic drill compressor front.jpg
A compressor for running a pneumatic jackhammer.

A pneumatic jackhammer, also known as a pneumatic drill or pneumatic hammer, [18] is a jackhammer that uses compressed air as the power source. The air supply usually comes from a portable air compressor driven by a diesel engine. Reciprocating compressors were formerly used. The unit comprised a reciprocating compressor driven, through a centrifugal clutch, by a diesel engine. The engine's governor provided only two speeds:

Modern versions use rotary compressors and have more sophisticated variable governors. The unit is usually mounted on a trailer and sometimes includes an electrical generator to supply lights or electric power tools.

Additionally, some users of pneumatic jackhammers may use a pneumatic lubricator which is placed in series with the air hose powering the air hammer. This increases the life and performance of the jackhammer. Specific lubricant is filled in the pneumatic lubricator. Furthermore, air compressors typically incorporate moisture into the compressed air leading to freeze-ups of the jackhammer or air hammer in cold weather.

Electro mechanical or electropneumatic

A single phase demolition breaker. Makita demolition breaker.jpg
A single phase demolition breaker.

An electropneumatic hammer is often called a "rotary hammer," because it has an electric motor, which rotates a crank. The hammer has two pistons—a drive piston and a free flight piston. The crank moves the drive piston back and forth in the same cylinder as the flight piston. The drive piston never touches the flight piston. Instead the drive piston compresses air in the cylinder, which then propels the flight piston against a striker, which contacts the drill bit. [19]

Electric powered tools come in a variety of sizes from about 12–65 lb (5.4–29.5 kg). They require an external power source, but do not require a compressor. Although in the past these tools did not have the power of an air or pneumatic hammer, this is changing with newer brushless-motor tools coming close to the power of a pneumatic tool and in some cases even matching it. Electric powered tools are useful for locations where access to a compressor is limited or impractical, such as inside a building, in a crowded construction site, or in a remote location and it is not come under earth moving equipment or tool.

Electropneumatic tools use a variety of chucks for attaching chisels, but the most common are SDS-max, 78 in (22 mm) Hex, TE-S, and 1 18 in (29 mm) Hex. The connection end size is also related to the breaking energy of the tool. For example, the Bosch and Hilti 12 lb (5.4 kg) tools both use SDS-max, while the Bosch, Hilti, and Makita 65 lb (29 kg) tools all use 1 18 in (29 mm) Hex connection. See hammer drills for more on electropneumatic hammering.

Hydraulic

An excavator-mounted hydraulic jackhammer being used to break up concrete. Excavator jackhammer.jpg
An excavator-mounted hydraulic jackhammer being used to break up concrete.

A hydraulic jackhammer, generally much larger than portable ones, may be fitted to mechanical excavators or backhoes and is widely used for roadwork, quarrying and general demolition or construction groundwork. These larger machine mounted breakers are known as Rig Mounted, or Machine Mounted Breakers. Such tools can also be used against vertical walls (or ceilings for that matter), since the vehicles involved are massive enough and powerful enough to exert the forces involved without needing the help of gravity in operating the tool. Pneumatic or hydraulic tools are particularly likely to be used in mines where there is an explosion risk (such as underground coal mines), since they lack any high-power electrical circuitry that might cause a triggering spark.

Hydraulic breakers usually use a hydraulic motor driving a sealed pneumatic hammer system, as a hydraulic hammer would develop a low strike speed and transfer unacceptable shock loads to the pump system.

Advances in technology have allowed for portable hydraulic breakers. The jackhammer is connected with hydraulic hoses to a portable hydraulic powerpack: either a petrol or diesel engine driving a hydraulic pump; or a mini-excavator or skid-steer via a power take-off driveshaft to the machine's hydraulic system. Hydraulic power sources are more efficient than air compressors, making the kit smaller, cheaper or more powerful than a comparable pneumatic version.

Bits (chisels)

Bit types include

Sharpening

Chisels may be resharpened in a shop or with an angle grinder with grinding disc. After resharpening, they must then be heat treated to restore the integrity of the steel before use. As an alternative, Hilti also manufacturers self-sharpening polygon and flat chisels in SDS-max, TE-S, and 1-1/8" Hex connection ends.

Health effects

A jackhammer with black silencer attached Pneumatic drill.jpeg
A jackhammer with black silencer attached

The sound of the hammer blows, combined with the explosive air exhaust, makes pneumatic jackhammers dangerously loud, emitting 100 decibels at two meters. Sound-blocking earmuffs must be worn by the operator to prevent a form of hearing damage, of which tinnitus is the main symptom. Most pneumatic jackhammers now have a silencer around the barrel of the tool.

Use has been linked to Raynaud syndrome.

Prolonged exposure to the pronounced vibration conducted by the tool can lead to blood-circulation failures in the fingers, a condition known as vibration white finger. Applying athletic tape is not very effective in preventing white finger but seems to help alleviate some of its discomfort. Pneumatic drill usage can also lead to a predisposition for development of carpal tunnel syndrome.

Some manufacturers of electro-pneumatic tools now offer vibration reduction systems to reduce the vibration felt by the operator. For example, the Hilti TE 3000-AVR has approximately the same impact energy of a 60 lb (27 kg) pneumatic hammer, but the vibration felt by the operator is significantly less (7  m/s2). Other manufacturers such as Makita, DeWalt and Bosch also offer electric tools with vibration dampening.

Using a jackhammer to break up concrete pavement may expose the operator to hazardous dust containing respirable crystalline silica. [20]

Related Research Articles

Pneumatics use of pressurized gas to produce mechanical motion

Pneumatics is a branch of engineering that makes use of gas or pressurized air.

Air compressor device

An air compressor is a device that converts power into potential energy stored in pressurized air. By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When tank pressure reaches its engineered upper limit, the air compressor shuts off. The compressed air, then, is held in the tank until called into use. The energy contained in the compressed air can be used for a variety of applications, utilizing the kinetic energy of the air as it is released and the tank depressurizes. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. An air compressor must be differentiated from a pump because it works for any gas/air, while pumps work on a liquid.

Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes. Compressed air is used for power tools such as air hammers, drills, wrenches and others. Compressed air is used to atomize paint, to operate air cylinders for automation, and can also be used to propel vehicles. Brakes applied by compressed air made large railway trains safer and more efficient to operate. Compressed air brakes are also found on large highway vehicles.

Compressor Mechanical device that increases the pressure of a gas by reducing its volume

A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.

For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, and hydraulic motors that are assembled into hydraulic machinery, hydraulic drive systems, etc. In pneumatics, air or another gas transfers force between pneumatic components such as compressors, vacuum pumps, pneumatic cylinders, and pneumatic motors. In pneumatic systems, the working gas also stores energy because it is compressible.

Drilling rig

A drilling rig is an integrated system that drills wells, such as oil or water wells, in the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person and such are called augers. Drilling rigs can sample subsurface mineral deposits, test rock, soil and groundwater physical properties, and also can be used to install sub-surface fabrications, such as underground utilities, instrumentation, tunnels or wells. Drilling rigs can be mobile equipment mounted on trucks, tracks or trailers, or more permanent land or marine-based structures. The term "rig" therefore generally refers to the complex equipment that is used to penetrate the surface of the Earth's crust.

Quasiturbine

The Quasiturbine or Qurbine engine is a proposed pistonless rotary engine using a rhomboidal rotor whose sides are hinged at the vertices. The volume enclosed between the sides of the rotor and the rotor casing provide compression and expansion in a fashion similar to the more familiar Wankel engine, but the hinging at the edges allows the volume ratio to increase. Unlike vane pumps, in which vane extension is generally important and against which the pressure acts to generate the rotation, the Quasiturbine contour seals have a minimal extension and the rotation does not result from pressure against these seals.

Pneumatic motor is a propulsion engine powered by compressed gas

A pneumatic motor or compressed air engine is a type of motor which does mechanical work by expanding compressed air. Pneumatic motors generally convert the compressed air energy to mechanical work through either linear or rotary motion. Linear motion can come from either a diaphragm or piston actuator, while rotary motion is supplied by either a vane type air motor, piston air motor, air turbine or gear type motor.

A pile driver is a device used to drive piles (poles) into soil to provide foundation support for buildings or other structures. The term is also used in reference to members of the construction crew that work with pile-driving rigs.

Rotary-screw compressor

A rotary-screw compressor is a type of gas compressor, such as an air compressor, that uses a rotary-type positive-displacement mechanism. They are commonly used to replace piston compressors where large volumes of high-pressure air are needed, either for large industrial applications or to operate high-power air tools such as jackhammers and impact wrenches.

A drifter drill or drifter is a hydraulic or pneumatic rock or ground drill used to make horizontal holes in tunnel construction and mining. It is mounted on a feed, which is like a rail that the drill travels on or drifts. This kind of drilling procedure is also called drifting. The feed is usually attached with a flexible boom to a stationary or mobile unit that contains the powerpack. Drifters are used in mining, construction, exploration, and natural science.

Free-piston engine

A free-piston engine is a linear, 'crankless' internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device and a load device.

Holman Brothers

Holman Brothers Ltd. was a mining equipment manufacturer founded in 1801 based in Camborne, Cornwall, UK.

A down-the-hole drill, usually called DTH by most professionals, is basically a mini jackhammer screwed on the bottom of a drill string. The fast hammer action breaks hard rock into small flakes and dust and is blown clear by the air exhaust from the DTH hammer. The DTH hammer is one of the fastest ways to drill hard rock. Now smaller portable drillcat drilling rigs with DTH hammers can drill as fast as much larger truck rigs with this newer technology. The system is thought to have been invented independently by Stenuick Frères in Belgium and Ingersoll Rand in the USA in the mid-1950s.

Rotary hammer type of rotary drill

A rotary hammer is a power tool that can perform heavy-duty tasks such as drilling and chiseling hard materials. It is similar to a hammer drill in that it also pounds the drill bit in and out while it is spinning. However, rotary hammers use a piston mechanism instead of a special clutch. This causes them to deliver a much more powerful hammer blow, making it possible to drill bigger holes much faster.

Steam hammer power hammer

A steam hammer, also called a drop hammer, is an industrial power hammer driven by steam that is used for tasks such as shaping forgings and driving piles. Typically the hammer is attached to a piston that slides within a fixed cylinder, but in some designs the hammer is attached to a cylinder that slides along a fixed piston.

Fluid deforms continuously on the application of shear stress, no matter how much small is it. Fluid comprises both gases and liquid. The technique of using liquid for power transmission is called as hydraulics while which uses gases for power transmission is called Pneumatics.In most hydraulic systems, mineral oils will be used while in most pneumatic systems, atmospheric air will be used.

Chicago Pneumatic, also known as "CP", is an industrial manufacturer providing power tools, air compressors, generators, light towers and hydraulic equipment. Products are sold in more than 150 countries through a worldwide distribution network. CP is active on markets such as tools for industrial production, vehicle service, maintenance repair operation for mining, construction, infrastructure equipment.

A bash valve is a valve within a piston engine, used to control the admission of the working fluid. They are directly actuated valves, operated by contact between the piston and the valve tip.

References

Air hose connection on pneumatic drill Aa pneumaticdrill hosecoupling 01.jpg
Air hose connection on pneumatic drill
  1. STEAM OR PNEUMATIC ENGINE
  2. https://books.google.com/books?id=BQZRAAAAYAAJ&pg=PA89&sig=ACfU3U27rENgbszFSCj83DB9lIFJl4f4Ag&focus=searchwithinvolume&q=Miller
  3. Brunton, C. (September 21, 1844) "Design of wind hammer for boring rocks," The Mechanics' Magazine, 41 : 203–204.
  4. West, Graham, Innovation and the Rise of the Tunnelling Industry (Cambridge, England: Cambridge University Press, 1988), p. 33.
  5. https://books.google.co.uk/books?id=83Xh0RxSoacC&pg=PA52&dq=Clarke+1846+11077+Patent&hl=en&sa=X&ved=0ahUKEwicjMbor_DYAhWCZ1AKHdLlA9kQ6AEINTAC#v=onepage&q=Clarke%201846%2011077%20Patent&f=false
  6. Henry S. Drinker,Tunneling, explosive compounds, and rock drills … (New York, New York: John Wiley & Sons, 1878), pages 153-157.
  7. Drinker (1878), page 160.
  8. Drinker (1878), page 164.
  9. Drinker (1878), page 266.
  10. The project was called the "Mount Cenis tunnel" although the tunnel passed under Mount Fréjus.
  11. Drinker (1878), page 152.
  12. Drinker (1878), pages 168 and 266.
  13. Drinker (1878), pages 151-152.
  14. Drinker (1878), pages 169 and 266.
  15. See: Drinker (1878), page 168. See also: page 2 of Eustace M. Weston, Rock drills: design, construction and use (New York, New York: McGraw-Hill, 1910).
  16. How It Works - Horobin, Wendy; Marshall Cavendish Corporation, Third Edition, Page 1195
  17. Ellis, Iain (7 September 2006). Ellis' British Railway Engineering Encyclopaedia. lulu.com. p. 371. ISBN   9781847286437 . Retrieved 17 February 2014.
  18. https://books.google.com/books?id=FXOtwx6IK_0C&pg=PA240
  19. Clint DeBoer. "How's It Work? Rotary Hammers". Pro Tool Reviews. Retrieved June 22, 2016.
  20. "Workplace Safety & Health Topics: Silica: Jackhammer". Centers for Disease Control and Prevention. 29 July 2013. Retrieved 20 December 2014. Publication date is date of last page update.