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A hand held electrically powered hammer comprises a housing, a motor, and a hollow spindle. A piston and a ram are located for reciprocation within the spindle. A casing encloses at least part of the spindle so as to define a chamber between the spindle and the casing. A damping mass is slideably su

A hand held electrically powered hammer comprises a housing, a motor, and a hollow spindle. A piston and a ram are located for reciprocation within the spindle. A casing encloses at least part of the spindle so as to define a chamber between the spindle and the casing. A damping mass is slideably supported by a spacer and is located within the chamber and is connected to the hammer housing via a spring so as to oscillate back and forth along the spindle to minimize the vibration of the hammer housing and also so as to generate air flows within the chamber for facilitating heat transfer from the spindle to the metal casing.

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1. A hand held electrically powered hammer, comprising a housing within which is located:a motor;a hollow spindle within which is located for reciprocation therein a piston and a ram;a hammer drive arrangement which converts the rotary drive of the motor to a reciprocating drive to the piston;a tool

1. A hand held electrically powered hammer, comprising a housing within which is located:a motor;a hollow spindle within which is located for reciprocation therein a piston and a ram;a hammer drive arrangement which converts the rotary drive of the motor to a reciprocating drive to the piston;a tool holder body in which a tool may be mounted for reciprocation;wherein the reciprocation of the piston reciprocatingly drives the ram via an air cushion such that repeated impacts from the ram are transmitted to a tool mounted in the tool holder body, and wherein the hammer additionally comprises:a casing which encloses at least part of the spindle so as to define a chamber between the spindle and the casing;a damping mass which is located within the chamber which damping mass is connected to the hammer housing via a spring element so as to oscillate back and forth along the spindle; andat least one spacer element slideably mounted on the spindle for positioning the damping mass between the spindle and the casing so that a first gap is present between the damping mass and the spindle and a second gap is present between the damping mass and the casing. 2. A hammer according to claim 1 wherein the casing encircles the spindle and the damping mass encircles the spindle and is concentric with the spindle. 3. A hammer according to claim 1 wherein the damping mass comprises a single piece cylinder. 4. A hammer according to claim 1 wherein the damping mass is made from one of steel and brass. 5. A hammer according to claim 1 wherein the spring element comprises a first spring located forwardly of the damping mass between the damping mass and one of the a forward part of the housing and the casing, and a second spring located rearwardly of the damping mass between the damping mass and one of a rearward part of the housing and the casing. 6. A hammer according to claim 1 wherein the spring element is a coil spring which encircles the spindle. 7. A hammer according to claim 1 wherein the damping mass and the spring element are arranged so that the damping mass oscillates back and forth along the spindle out of phase with the beat frequency of the piston. 8. A hammer according to claim 1 wherein the damping mass and the spring element are arranged so that the damping mass oscillates back and forth along the spindle approximately 180° out of phase with the beat frequency of the piston. 9. A hammer according to claim 1 wherein the oscillation of the damping mass within the chamber generates an air flow in one of the first gap and the second gap. 10. A hammer according to claim 1 wherein the spacer element is formed integrally with the damping mass. 11. A hammer according to claim 1 wherein the spacer element comprises a guide arrangement and the damping mass is mounted on the guide arrangement and the guide arrangement is shaped to define at least one channel through which air can flow. 12. A hammer according to claim 1 wherein the spacer element comprises a guide ring. 13. A hammer according to claim 1 wherein the damping mass and the casing encircle the spindle and the spacer element comprises a guide ring and the damping mass is mounted on the guide ring and the guide ring includes ribs formed on the radially inward facing surface of the guide ring, and whereby the guide ring and ribs and spindle define at least one channel through which air can flow. 14. A hammer according to claim 1 additionally comprising a fan for generating airflow over the outer surface of the casing. 15. A hammer according to claim 1 additionally comprising a fan arrangement for generating airflow and a labyrinth for directing the airflow over the outer surface of the casing, and wherein the fan generates airflow which passes over the motor, through the fan and then through the labyrinth and over the casing before exhausting from the housing. 16. A hammer according to claim 1 wherein the hammer housing comprises an inner metal housing arrangement in which the moto r, hammer drive arrangement and spindle are mounted and an outer plastic housing rigidly fixed to the inner metal housing. 17. A hammer according to claim 16 wherein the casing is fixed to the inner metal housing arrangement. 18. A hammer according to claim 1 wherein the chamber is vented into the hammer housing. 19. A hand held electrically powered hammer, comprising:a housing;a motor;a hollow spindlea piston and a ram located within the spindle for reciprocation therein;a hammer drive arrangement which reciprocatingly drives the piston;a tool holder body in which a tool may be mounted for reciprocation;a casing which encloses at least part of the spindle so as to define a chamber between the spindle and the casing;a damping mass which is located within the chamber which damping mass is connected to a spring element so as to oscillate back and forth along the spindle; andat least one spacer element slideably mounted on the spindle for positioning the damping mass between the spindle and the casing so that a gap is present between the damping mass and one of the spindle and the casing.