Hammer Drills

Abstract

A hammer drill has a spindle for receiving the stem of a drilling tool. The spindle is rotatably driven by a drive shaft arranged parallel thereto and has a striker adapted to move into the spindle and strike the drilling tool disposed therein. The striker is cyclically withdrawn in opposition to a spring and released into striking engagement with the drilling tool disposed in the spindle by means of a ballistic cam mounted on the drive shaft. Upon removal of a drilling tool from a workpiece, the striker mechanism is deactivated.

Description

FIELD OF THE INVENTION

The invention relates to a hammer drill having a tool spindle for receiving the stem of a drilling tool and arranged to be rotatably driven by a drive shaft arranged parallel to the axis of the spindle. The provided hammer drill has a striking mechanism including a striker member which projects into the tool spindle and is arranged to be cyclically withdrawn against a spring and then released for a striking movement by a ballistic can carried on the drive shaft for rotation thereby. The hammer drill hereinafter described may function solely as a drill with no hammer action by means of a cam disengagement as will hereinafter be explained in greater detail.

THE PRIOR ART

In known hammer drills of the kind hereinafter described which can be selectively adjusted from hammer drilling to drilling only by switching on or off the drive from the striking mechanism, the striking mechanism still operates, that is, runs idly if the machine is not pressed against a workpiece but is removed from it. The striking energy thus developed by the hammer drill while idling is not led usefully away from the tool, but remains in the mechanism where it is frequently changed into harmful heat and into distortion of material by expensive machine parts, for example a set of plate springs serving as striking pads. In any event, vibration of the drilling machine results which not only makes its operation difficult but in addition leads to correspondingly great vibration of all machine components, for example, its anchor components whereby the life of these parts is shortened. Moreover, an unpleasant noise results from the inefficient operation of the striking mechanism when the machine idling in a nonworking position.

SUMMARY

It is an object of this invention to provide a hammer drill which does not have the above-mentioned defects but has a striking mechanism which automatically becomes deactivated upon removal of the drill from a workpiece.

It is another object of this invention to provide a cam disengaging switch which readily disengages the strike-creating cam from a coupling member whereby the striker member is deactivated from striking the tool-holding spindle and the hammer drill may continue to operate as a drill.

Also according to the invention hereinafter described in detail, the striker member of the provided hammer drill can be hollow, with both an anvil spring and a spring stop bolt projecting into the hollow member. The spring is supported at its front end either on an inner shoulder provided in the striker member or on an outer shoulder of the spring stop bolt, according to the position of the striker member utilizing such construction. The striker member spring is trapped or held by the bolt shortly before the impact of the striker member on the tool stem, so that the striker member performs a small movement before it strikes the tool.

Thus it is a further object of this invention to provide a hammer drill structural arrangement whereby the kinetic energy of the striker member is transferred in full to the tool and the striker member is not additionally urged by the striker member spring into engagement with the tool so that disadvantageous rebounds within the drill are prevented. Furthermore, because of the bolt, the pressure on the tool requred when returning to the tool to the workpiece is reduced insofar as one no longer has to work against the force of the striker member spring.

Thus it is a still further object to provide a hammer drill in which the tool may be reset into working position with a minimum of effort.

In one embodiment of this invention a hammer drill is provided having a hollow spindle for receiving a drilling tool. A drive shaft is arranged to rotate the spindle and extends parrallel thereto. A striker member is receivable in a rear portion of the spindle, and a ballistic cam on the drive shaft is arranged to be rotated thereby to cause the striker member to be cyclically withdrawn against a spring and released to effect a striking action against the hollow spindle. The striker member is adapted to advance beyond the normal striking position on removal of the tool from a workpiece and thereby prevent rotation of the ballistic cam.

Upon withdrawal of the drilling tool from a workpiece, the hollow spindle and tool slip forward somewhat, thus permitting the striker member or anvil to proceed forward beyond its normal striking plane and thus prevent the ballistic cam by which it is driven from rotating further on the drive shaft. Thus upon removal of the machine from the work, its striking mechanism is stopped, so that the stresses associated with it and the disturbing effects such as vibration and additional machine noise are prevented.

According to a further feature of the invention, the cam is arranged to be rotatable and axially displaceable on the drive shaft as well as being urged by a spring into coupling engagement with a coupling member torsionally connected with the drive shaft. This coupling member is, however, disengaged as soon as the striker member or anvil extends forward further than normal on removal of the machine from the work, thus immobilizing the ballistic cam which is displaced axially as a consequence by a corresponding amount away from the coupling member on the drive shaft, therefore moving out of rotational engagement with the coupling member. For this purpose, clutch dogs on the coupling member and the cam are provided with correspondingly inclined sides.

In order to keep the cam securely in the furthest advanced position of the striking anvil and out of engagement with the coupling member, a check or stop member is provided in the ballistic cam which is arranged to be radially displaceable and is provided with a resiliently supported ball. This stop member is disposed with its inner end in an annular groove in the drive shaft while engaged with a tension element provided on the striking anvil. The tension element cooperates with the ballistic cam while the striker member is in the outermost advanced position engaging the ball of the check member.

The striker member or anvil is also preferably positively located in its outermosr advance position. For this purpose a groove is provided around the anvil into which is received a retaining ring, for example, an O-ring provided on the tool spindle, when the anvil is at its outermost advance position.

In order to change the machine from striking or hammer drilling to a simple drilling mode of operation, there is a switch member provided in the machine casing which can be rotatably adjusted from outside, and which allows the ballistic cam to come out of engagement with the coupling member by axial displacement, thereby stopping the striking mechanism.

DESCRIPTION OF THE DRAWINGS

By way of example, a hammer drill embodying the invention is described hereinafter and illustrated in the accompanying drawings, in which:

FIGS. 1, 2 and 3 are fragmentary elevational views, partly in section, which schematically show part of the mechanism of the hammer drill in different working and adjusting phases; and

FIG. 4 is a fragmentary sectional side view partly in elevation of a hammer drill made pursuant to this invention

DESCRIPTION OF THE INVENTION

The hammer drilling machine shown in FIG. 4 has a housing 1 comprising several portions of which the rearmost portion, which is not illustrated, accommodates an electric motor. The armature spindle 2 of the motor is journalled in a middle housing portion 1' by means of a roller bearing 3. The forwardly projecting end of the spindle 2 carries or is formed as a pinion 4 in engagement with a pinion 6 mounted on a drive shaft 5. The drive shaft transfers the rotating drive of the spindle 2 by means of a pair of meshing gear wheels 7 to a tool holder shaft 8 rotatably journalled in the front portion of the housing 1 by roller bearings 9, 10. The axes of the tool holder shaft 8, the drive shaft 5 and the armature spindle 2 are parallel. A drilling tool 11 with a stem 11' is received in a bore 8' opening from the forward end of the tool holder shaft 8, the stem 11' having a multi-sided cross-section corresponding to that of the bore 8'.

A striker member or anvil 12 has a stem 12' projecting into the bore of the tool holder shaft 8 from the rear. The anvil 12 is provided with a channel 13 extending around it, into which a reslient retainer ring 14, preferably a conventional O-ring, engaging on a rear surface of the tool holder shaft 8, engages when the anvil is in its outermost advanced position. In this way, the anvil 12 is restrained against movement from its outermost advance position.

An anvil spring 15 and a spring stop bolt 16 project fro the rear into the interior of the anvil 12. The spring 15 is supported at its rear end on a spring plate 15' in the middle housing portion 1' and the stop bolt 16 is attached at its rear end to this housing portion 1' by means of a transversely extending pin 17. The forward end 16' of the spring stop bolt is outwardly flared like a trumpet and forms an outer shoulder serving as an abutment for the spring, as shown in FIG. 4. Depending on the position of the anvil 12, the spring 15 is supported equally well on an inner shoulder 12' provided in the anvil. By this arrangement, the kinetic energy of the anvil 12 is transferred completely to the tool 11, without causing undesirable rebounds through the spring 15.

A tension element 12'" is provided on the anvil 12 for cooperation with a ballistic cam 18 mounted for rotation and axial displacement on the drive shaft 5. By means of clutch dogs 18", the cam 18 can be engaged in a manner enabling transmission of strong torsional forces with inclined sides 19'of a clutch or coupling member 19, which is securely mounted on the drive shaft 5 for rotation therewith. A spring 20 functions to urge the ballistic cam 18 into this coupling engagement with the coupling member 19. By means of the rotation of the ballistic cam 18, having a sliding surface 18" on which the tension element 12'" of the anvil 12 can slide, the anvil is periodically withdrawn against the force of the spring 15 and then released to advance and effect its striking movement.

FIG. 1 shows the normal position of the striking mechanism. The stem 11' of the tool 11 extends so far into the tool spindle 8 that the anvil 12 comes to rest with the tension element 12'" on the sliding surface 18" of the cam 18. In this condition, the coupling member 19 causes the ballistic cam 18 to rotate with it. Since the ballistic or sliding angle .alpha. between the sliding surface 18" and the plane extending through the tension element 12'" is smaller than the angle .beta. of the sides of the clutch dogs 18', the force P between the cam 18 and the tension element 12'" is greater than the forece Q between the dogs 18' and the clutch element 19. Consequently, the ballistic cam 18 cannot rise up the inclined sides 19' of the coupling member 19 but remains securely coupled thereto.

If the hammer drill is lifted up so as to withdraw the tool 11 from a workpiece, then the anvil 12, as shown in FIG. 2, moves forward beyond its normal range of impacting movement to a position in which it is firmly held by engagement of the O-ring 14 in the channel 13. Since in this position the previously-mentioned sliding angle .alpha. is greater than the angle .beta., the force Q is greater than the force P. The ballistic cam 18 is consequently displaced axially from the clutch member 19 and is so uncoupled from it. The cam 18 thus reaches an idling position illustrated in FIG. 3. The cam 18 is retained in this position by a stop member 21 which is received in the cam for displacement radially of it. The stop member 21 is provided at its outer end with a ball 22 urged outwardly by a spring 21'. The tension element 12'" of the anvil 12 presses against this ball 22 in the outermost advance position of the anvil. The stop member 20 is thereby pressed inward so as to enter an annular groove 5' in the drive shaft 5, the cam 18 being then axially displaced by a corresponding amount so that sufficient idling clearance 23 remains between the dogs 18' and the coupling member 19. When the hammer drill is again pressed against the workpiece, the anvil 12 is pushed back from its most advanced position by the drilling tool 11, so that the stop member 21 is freed from engagement by the tension element 12'" of the anvil 12. The ballistic cam 18 is thus displaced in the direction towads the coupling member 19 by the spring 20, so that the clutch dogs 18' jump back into the corresponding coupling recesses on the coupling member. The working position illustrated in FIG. 1 has then been reporduced.

The mode of operation of the machine can be changed from hammer drilling to simple drilling. A control rod 26 journalled in the front part of the housing 1, for rotation between various angular positions, is provided at its inner end with an inclined end surface 26'. The cam 18 can be released from its coupling with the coupling member 19 by axial displacement of the cam due to appropriate rotation of the control rod 26, whereby rotation of the cam 18 and thus the whole striking mechanism will remain switched off even when the machine is pressed against the workpiece, and the machine operates simply as a drill.

Claims

What is claimed is:

1. A hammer drill having a hollow spindle for receiving a drilling tool, a drive shaft arranged to rotate the spindle and extending parrallel thereto, a striker member receivable in the spindle, and a ballistic cam on the drive shaft arranged to be rotated thereby to cause the striker member to be cyclically withdrawn against a spring and released to effect a striking action; the striker member being arranged to advance beyond the normal striking position on removal of the tool from a workpiece and thereby prevent rotation of the ballistic cam; said ballistic cam being rotatable and axially displaceable on the drive shaft and urged by a second spring towards coupling engagement with a coupling member having clutch dogs and said ballistic cam having sides inclined at an angle to a plane transverse to the drive shaft greater than the angle between the plane and surfaces of the ballistic cam and of the striker member which slidably engage during the withdrawal of the striker member.

2. A hammer drill having a hollow spindle for receiving a drilling tool, a drive shaft arranged to rotate the spindle and extending parallel thereto, a striker member receivable in the spindle, and a ballistic cam on the drive shaft arranged to be rotated thereby to cause the striker member to be cyclically withdrawn against a spring and released to effect a striking action, the striker member being arranged to advance beyond the normal striking position on removal of the tool from a workpiece and thereby prevent rotation of the ballistic cam; said ballistic cam being rotatable and axially displaceable on the drive shaft and urged by a second spring towards coupling engagement with a coupling member mounted to rotate with the drive shaft; said coupling member having clutch dogs and said ballistic cam having sides inclined at an angle to a plane transverse to the drive shaft greater than the angle between the plane and surfaces of the ballistic cam and of the striker member which slidably engage during the withdrawal of the striker member; said ballistic cam also having a radially displaceable stop member including a resiliently supported ball whereby the ballistic cam is held at an axial position of disengagement from the coupling member when the striker member is advanced beyond the normal striking position.

3. A hammer drill having a hollow spindle for receiving a drilling tool, a drive shaft arranged to rotate the spindle and extending parrallel thereto, a striker member receivable in the spindle, and a ballistic cam on the drive shaft arranged to be rotated thereby to cause the striker member to be cyclically withdrawn against a spring and released to effect a striking action, the striker member being arranged to advance beyond the normal striking position on removal of the tool from a workpiece and thereby prevent rotation of the ballistic cam; said ballistic cam being rotatable and axially displaceable on the drive shaft and urged by a second spring towards coupling engagement with a coupling member mounted to rotate with the drive shaft; said coupling member having clutch dogs and said ballistic cam having sides inclined at an angle to a plane transverse to the drive shaft greater than the angle between the plane and surfaces of the ballistic cam and of the striker member which slidably engage during the withdrawal of the striker member; said ballistic cam also having a radially displaceable stop member including a resliently supported ball whereby the ballsitic cam is held at an axial position of disengagement from the coupling member when the striker member is advanced beyond the normal striking position; the inner end of said stop member engaging an annular groove in the drive shaft when the striker member engages the ball of the stop member with the striker member advanced beyond the normal striking position.