Devices of this type are used for cleaning surfaces and to this end comprise a bundle of metal needles. Other devices of the same type comprise a cutter and are used for example to eliminate the welding seam which projects at the junction of two parts, to eliminate excess material at the seam, etc. Extended use of these devices is difficult because of the noise and on account of the vibrations of the device.
Another type of percussion device is known which has no anvil or free piston, but two co-axial pistons pressed against one another by two springs moving towards and away from one another alternately under the action of a pneumatic drive mechanism. A device of this type is relatively quiet, but is limited to low power and its output in relation to the volume of compressed air consumed is very poor. In view of their low power, these devices cannot be used for operations such as cleaning rusted metal sheets or working on concrete surfaces.
It has already been proposed to reduce vibrations produced by percussion tools, in particular vibrations transmitted to the housing and gripping members of the tool and which result in increased fatigue for the operator and thus in lower performance during extended use. This is the case in particular in French Pat. No. 1 059 349, in which a cylinder is mounted to slide longitudinally between two springs in a housing rigid with a handle. A mounting sliding longitudinally between two springs is also disclosed in French Pat. No. 1 154 429 and U.S. Pat. No. 3,788,404. This spring mount effective in the longitudinal direction of the percussion mechanism in the housing should normally permit a quite considerable damping effect of the vibrations to be obtained insofar as as the free piston of the percussion mechanism moves longitudinally. However, vibrations are transmitted to the housing by all the contact surfaces, in particular by the guide surfaces of the slide mechanism in the housing. Guiding must be carried out with sufficient precision, in the absence of which wear between the moving parts increases rapidly and results moreover in heating and expansion of the housing which thus rapidly becomes inoperative.
The spring mount of the above-mentioned solutions is furthermore limited to pneumatic tools supplied axially with compressed air via the rear end. This method of supply is not suitable for small manual devices such as pneumatic needle or cutter guns. These devices are provided with a lateral handle, hence the title "gun", and it is therefore much more practical to supply the striking mechanism laterally via the handle. However, the lateral supply presupposes perfect sealing between the housing and the striking mechanism which necessitates close contact between the mechanism which produces vibrations and the housing.