ROTARY PERCUSSIVE DRILL

Abstract: A mode change mechanism for a rotary percussive drill comprises locking balls (13) engaged in axial recesses (10) in a beat piece (7) that transmits percussion from a percussive drive (5, 6) to a drill bit and a rotary collar (16) for moving the locking balls (13) and the beat piece (7) from a position in which the beat piece is able to transmit percussion to one in which transmission cannot take place.

Description: ROTARY PERCUSSIVE DRILL This invention relates to rotary percussive drills and has particular reference to hand-held rotary percussive drills fitted with a control enabling the user to decouple the percussive drive when required to enable the drill to be used in a rotary mode. In some forms of rotary percussive drill, hammer blows are imparted to a drill bit or other tool via a beat piece and it has been proposed to provide a useroperated control which acts to hold the beat piece clear of the percussive drive when it is desired to use the percussive drill in the rotary mode. The control, when actuated by the user urges locking elements into an annular groove in the beat piece so holding the latter in a position in which it is clear of the percussive drill. However, it is found that the locking elements will not always engage with the groove and this results in failure to hold the beat piece clear of the percussive drive so that the beat piece continues to transmit that drive to the drill bit or other tool. Accordingly, it is an object of the present invention to provide a construction in which the problem referred to in the preceding paragraph is overcome. According to the present invention, a rotary percussive drill comprises a bit holder, driving means for imparting rotation to the bit holder, a percussive drive, a beat piece for transmitting percussion from the percussive drive to a bit when positioned in the holder characterised in that the beat piece has at least one elongate axial recess on its outer surface, the recess being engaged with locking elements, and an arrangement for moving the locking elements between a first position in which the beat piece is in operative engagement with the percussive drive and transmits percussion from the percussive drive to the bit, and a second position in which the beat piece is operatively disengaged from the percussive drive and cannot transmit percussion from the percussive drive to the bit. In one embodiment of the invention, the locking elements comprise balls located in the recess and in engagement with a member movement of which effects operative engagement and disengagement of the beat piece and the percussive drive. The movable member may be of generally tubular form and mounted for rotation about the axis of the beat piece. The bore of the tube being formed with acam surface so contoured that on rotation of the movable member the locking elements are moved axially to effect operative engagement or disengagement of the beat piece and the percussive drive. By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawing which shows the embodiment in cross section. The rotary percussive drill has a bit holder in the form of a tubular sleeve 1 one end of which has teeth 2 which engage a bevel gear 3 through which rotation about its longitudinal axis is imparted to the sleeve 1. The bevel gear is driven by an electric motor 4 which also provides a percussive drive through the medium of a pneumatically-actuated ram 5 reciprocable in a hollow piston 6. The use of pneumatically-actuated rams to provide percussive action is well known and will not be described further. Movable along the bore of the sleeve 1 is a beat piece 7. The beat piece is located between the ram 5 and a bit (not shown) but which is held in the sleeve 1 by releasable locking balls 8 and rotatable by the sleeve 1 via driving elements one of which is indicated at 9. The beat piece 7 has two diametrically opposed axial recesses 10 located between the nose 11 of the beat piece and an end portion 11a of reduced diameter as compared with the remainder of the beat piece and is located in a smaller diameter bore 12 of the beat piece. The recesses 10 accommodate locking elements in the form of balls 13 that locate permanently in the recesses 10 and engage the surface of an annular holder 14 through axial slots 19 in the bit holder sleeve 1, the holder 14 maintained in contact with the cam face 15 of a mode change control member 16 of generally tubular form by a helical spring 17. With the above-described components in the positions shown in the drawing, the beat piece 7 is, in use, cyclically impacted by the nose 18 of the ram 5 as the latter is reciprocated in the hollow piston 6 and those impacts are transferred by the beat piece 7 to the bit. At the same time, the sleeve is rotated about its longitudinal axis by the drive transmitted to gear 3 and this rotation is transferred to the bit by the driving elements 9. It will be appreciated that the axial length of the recess 10 is sufficient to permit the required reciprocatory movement of the beat piece. If now the user wishes to use the drill in the nonhammer mode, the mode change control member 16 is rotated so moving the balls 13 to the left as seen in the drawing and along the slots 19 and the recess 10. The balls 13 contact the left-hand (as seen in the drawing) end of the recess 10 and continued rotation of the member 16 moves the beat piece 7 to the left (as seen in the drawing) by an amount sufficient to provide clearance between the end 11a and the nose 18 of the ram 5 when the latter is at the end of its impacting stroke. When in this position, the beat piece 7 is not impacted by the nose of the piston and the bit is subject only to rotary movement. To revert to the hammer mode, the member 16 is rotated in the reverse direction so allowing the balls 13 to return, under the action of spring 17, to the position shown in the drawing and, when the user presses the bit against a workpiece, allowing the beat piece 7, to resume its active position in which it is impacted cyclically by the nose 18 of the piston 5. The cam face 15 of the control member 16 may be so contoured that a 900 or 1800 rotation of the member 16 is needed to complete the required axial movement of the balls 13 along the slots 19. The contour of the cam face 15 may, alternatively, be such that further rotation of the member 16 in the same direction allows the balls 13 to be returned to their original positions. It will be appreciated that members of shapes other than spherical may be used in place of the balls 13 and that the beat piece may have a separate axial recess for each such member whether it is a ball or not. In addition, the control member 16 may be adapted to be moved axially and not rotated to effect the- change between the hammer and non-hammer modes. Finally, it will be understood that, in the above described embodiment the bit is subjected to percussive action of the beat piece only when the bit is pressed by the user into contact with a workpiece. Such pressure resulting in a small inward movement of the bit into the sleeve and of the beat piece towards the ram.

Claims: CLAIMS 1. A rotary percussive drill comprising a bit holder (1), driving means (3) for imparting rotation to the bit holder, a percussive drive (5, 6) a beat piece (7) for transmitting percussion from the percussive drive to a bit when positioned in the bit holder, characterised in that the beat piece (7) has at least one elongate axial recess (10) in its outer surface, at least one locking element (13) engaged in the axial recess (10) and an arrangement (14-16) for moving the or each locking element (13) between a first position in which the beat piece (7) is able operatively to engage the percussive drive to transmit percussion to the bit and a second position in which the beat piece (7) is held operatively disengaged from the percussive drive (5,6) and cannot transmit percussion to the bit. 2. A rotary percussive drill as claimed in claim 1 in which the axial length of each recess (10) is sufficient to accommodate the movement of the beat piece (7) when transmitting percussion from the percussive drive (5, 6) to the bit. 3. A rotary percussive drill as claimed in claim 2 ir which each locking member (13) is operatively engaged with a holder (14) movement of which effects said engagement and disengagement of the beat piece (7) and the percussive drill. 4. A rotary percussive drill as claimed in claim 3 in which the holder (14) is resiliently biassed into engagement with a member (16) movable between first and second positions to effect movement of the locking elements (13). 5. A rotary percussive drill as claimed in claim 4 in which the movable member (16) is of tubular form and is rotatable about the axis of the beat piece (7). 6. A rotary percussive drill as claimed in claim 5 in which the movable member (16) has a cam surface (15) in engagement with the holder (14). 7. A rotary percussive drill as claimed in claim 6 in which the cam surface (15) is so contoured that rotation of the movable member (16) through at least 900 is required to move the locking element (13) between its first and its second position. 8. A rotary percussive drill as claimed in claim 6 in which the cam surface (15) is so profiled that rotation of the movable member (16) through at least 900 effects movement of the locking member (13) from the first to the second position, and that continued rotation of the movable member (16) in the same direction effects movement of the locking member (13) from the second to the first position. 9. A rotary percussive drill as claimed in claim 1 in which the beat piece (7) has two diametrically opposed axial recesses (10), there being two locking members (13) of which one is located in one recess and the other in the other recess. 10. A rotary percussive drill as claimed in claim 9 in which each locking member (13) is a ball.

Inventors: SIMPSON, FRANK FLINTOFT
Applicants: BLACK & DECKER INC.
Application year: 1981
Main classification: B25D16
IPC codes: B25D16