Jackhammer

A pneumatic drill or jackhammer is a portable percussive drill powered by compressed air. It is used to drill rock, break up pavement, among other applications. It works similar to a hammer and chisel, by jabbing with its bit, not rotating it. (A drill driven by compressed air, which rotates its cutting bit is called an air-drill or familiarly, a windy-drill or rotary hammer.) The word "jackhammer" is used in North American English and in Australia, and "pneumatic drill" is used colloquially elsewhere in the English speaking world, although "(road) breaker" is used in the trade.

Overview

The portable pneumatic jackhammer is impractical for use on walls and steep slopes, as it relies on the inertia of the mass of its body to drive the bit into the work, and manipulating that mass when not supported by the work is difficult. Also, gravity is required to bring the mass back into contact with the work after each blow. Though it is unhealthy practice, the operator may lean on the tool to assist but is not really capable of overcoming the forces involved when not assisted by gravity. A technique developed by experienced laborers is the use of two man teams to overcome this obstacle of gravity. One laborer 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 ones head.

Its pneumatic hose connections are designed so that any hose will connect with any other hose without attention to male and female hose-ends. see Gender of connectors and fasteners.

Air supply

The air supply for a jackhammer usually comes from a portable 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:

* idling, when the clutch was disengaged
* maximum, when the clutch was engaged and the compressor was running

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. Makes of portable compressor sold in the UK include Atlas Copco, CompAir and Ingersoll Rand.

Hydraulic operation

A hydraulic jackhammer, 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. In mining, it is possible to use this against a vertical wall as the machine can be braced against the opposite wall of the gallery or some comparable device. Pneumatic tools are likely to be used in underground coal mines due to safety concerns.

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.

Electro-mechanical operation

While the term "jackhammer" is occasionally used to mean "pneumatic drill", the electromechanical tool that performs the same function is normally the one called a "jackhammer" in Britain. This tool is useful where the work is light and inaccessible to compressor.

The Makita breaker pictured uses standard 25mm (1") points and chisels identical to the ones used in medium sized pneumatic tools. It uses 1300 Watts of power and weighs about 19 kg (about 42 pounds) with a point installed.

This type and size of machine is commonly rented by amateurs for renovation jobs.

Health

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, which is the black item in the image below.

Prolonged exposure to the pronounced vibration set up by the tool can lead to blood-circulation failures in the fingers, a condition known as white finger. Applying athletic tape is not 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.

Bits

* Spade - provides flat finish for concrete or edging in asphalt or dirt
* Flat tip - allows direction control or finer edge finish
* Point - general breaking
* Stake driver - drives concrete form stakes
* Scrabbler - finishes surface smooth or for cleaning prior to bonding

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External links

* [http://www.builderbill-diy-help.com/jackhammer.html Using a jack hammer] non commercial help site.