[0001] This invention relates to rotary/ percussive portable, power-operated drills, that
is to say drills which can be operated with percussive action in addition to the normal
rotary action when required, e.g. for drilling masonry. The percussive action is produced
by co-operation between a ring of axially facing teeth formed on a member fixed to
the main driving shaft and a similar ring of teeth on an annular member which is held
against rotation. As described in our prior patent specification no; 1,366,572, the
member which is held against rotation is in the form of a ring which is fixed to the
housing of the drill. With such a construction, a large proportion of the vibration
generated by the co-operation between the two sets of teeth is transmitted back to
the user through the housing of the drill, thus making the operation uncomfortable
for the user.
[0002] A large proportion of this vibration can be eliminated if, instead of being fixed
to the housing, the co-operating ring is spring loaded so as to be capable of movement
in an axial direction, but being prevented from rotation under the frictional torque
produced by co-operation between the two sets of teeth. With this modified construction,
the ring needs to have considerable inertia in order to ensure that a large proportion
of the percussive movement is transmitted to the driving shaft and hence to the bit
of the drill. The ring thus takes the form of a spring-loaded anvil member which absorbs
a large part of the vibration which would otherwise be transmitted to the user, but
ensures that adequate percussive action is transmitted to the bit of the drill. The
mounting of this anvil member must be so designed as to prevent rotation while at
the same time not impeding the axial movement. For this purpose it has been proposed
to mount the anvil member by means of ball bearings located in axially extending grooves
in the anvil member and in the inner surface of the housing of the drill respectively.
Although producing good results, such a construction is expensive to produce, involving
accurate grinding of the surfaces involved.
[0003] According to the present invention, the anvil member is mounted to yield in an axial
direction by means of a coupling comprising a number of axially extending springs
surrounding and guided by pins located in corresponding counter bores, one part of
the coupling being fixed to the housing and the other to the anvil member, whereby
to prevent rotation of the latter. Preferably the pins are fixed to the housing of
the drill and the counter bores are formed in the anvil member, since this saves space
by avoiding the need for a separate part of the housing which is long enough to accommodate
the counter bores. Somewhat surprisingly, it is found that such an arrangement, while
preventing rotation of the anvil member, nevertheless imposes very little restriction
on the movement in an axial direction. Moreover, by avoiding the need for accurately
ground surfaces, the construction is simplified and made considerably cheaper.
[0004] Most conveniently three equi-angularly spaced springs are used together with associated
pins and counter bores, but this is not essential and other numbers are also possible.
[0005] An example of a construction in accordance with the invention will now be described
in more detail with reference to the accompanying drawing which is a mainly sectional
view of the forward portion, i.e. the portion closest to the chuck, of a portable,
rotary/percussive drill, the part above the centre line showing one position of the
main driving shaft in which a percussion mechanism is dis-engaged and the portion
below the centre line showing, in elevation, the alternative position of the shaft
in which the percussion mechanism is engaged.
[0006] The housing of the drill is shown as 1 and supports a main driving shaft 2, of which
the part above the centre line shown as 2A is shown in a longitudinal position corresponding
to disengagement of a percussion mechanism indicated generally as 3,while the part
2B below the centre line is shown in a longitudinal position corresponding to engagement
of the percussion mechanism 3. The electric driving motor and the reduction gearing
are not illustrated, but the gearing terminates in a pair of gear wheels 4 and 5 which
are splined to the shaft 2 so as to permit sliding motion of the shaft between the
positions 2A and 2B. The shaft 2 rotates in a pair of bearings, that at the rear end
shown as 7 permitting sliding movement of the shaft as illustrated and that at the
forward end shown as 8, being a thrust bearing which enables the longitudinal position
of the shaft to be adjusted. For adjustment purposes an annular member 9 formed with
a grip ring 10 has a helical end face of which the highest point is shown as 12A and
the lowest point as 12B. This co-operates with a complementary helical end face on
a fixed ring 13 so that when the member 9 is in the angular position illustrated above
the centre line, the member is forced to the left and when in the position below the
centre line it moves to the right.
[0007] A helical compression spring 15 enclosed by a cap member 16 acts on the thrust bearing
8 to force it against a shoulder 14 on the member 9. Operating pressure on the drill
bit applied to the shaft 2 pushes the cap 16 to the right until the cap engages the
bearing 8. When in the position illustrated above the centre line this movement is
not sufficient to engage the percussion mechanism 3 and a purely rotary motion is
applied to the shaft. When in the position below the centre line, however, the percussion
mechanism is engaged and a percussive action is superimposed on the rotary motion
as will now be described.
[0008] The percussion mechanism 3 includes a ring 21 which is fixed to the shaft 2 and turns
in a bearing 22 fixed within a liner 23 within the housing 1. The right hand end face
of the ring 21 is formed with a set of teeth 25, the configuration of which is best
seen from the elevational view below the centre line. A set of corresponding teeth
26 is formed on the end face of an annular anvil member 28 which forms a relatively
loose running fit both with the shaft 2 and with the interior of the liner 23. The
anvil member 28 is coupled to the liner 23 and hence to the housing 1 by three pins
30 located at intervals of 120° around the shaft 2. The three pins 30 are supported
by a ring 31, passing through corresponding holes in the ring 31 and into holes in
the liner 23. To the left of the ring 31, each pin 30 is formed with an enlargement
33 and the portion of each pin extending to the left beyond the enlargement 33 forms
a loose guide for a compression spring 35 located within a counter bore 36 formed
in the anvil member 28. The effect of the three springs 35 is to bias the anvil member
28 to the left into contact with a circlip 38 which is spaced from the bearing 22
by a ring 39.
[0009] Accordingly, when the main shaft is in the position 2A, it can rotate freely without
affecting the anvil member 28. On the other hand, when it is in the position 2B and
the rings of teeth 25 and 26 are in engagement, rotation of the shaft 2 is accompanied
by a percussive action as successive teeth ride over one another and then fall into
the adjacent recesses. This motion is transmitted to the shaft 2 which is intermittently
forced to the left against the effect of the spring 15, but vibration which would
otherwise be transmitted to the housing 1 of the drill is absorbed by movement to
the right of the anvil member 28 against the effect of the springs35. As previously
mentioned, it is necessary for the anvil member 28 to have appreciable mass and hence
corresponding inertia since otherwise a large proportion of the percussive action
generated would be absorbed by the anvil member rather than being transmitted to the
main shaft and hence to the bit. As it is, a major proportion of the percussive action
is transmitted to the shaft and all or virtually all of the remainder is absorbed
by the anvil member 28, thus avoiding discomfort to the user.
[0010] Since the anvil member 28 is a slack fit both on the shaft 2 and within the liner
23, there is no restraint on its axial movement. The reaction between the sets of
teeth 25 and 26, however, also generates a frictional torque and it is found that
this is resisted by the combination of the pins 30 and the springs 35 within their
counter bores 36 without the generation of excessive heat and without the need for
any excessive accuracy in machining the parts in question.
1. A rotary/percussive portable, power-operated drill in which percussive action is
transmitted to the rotary shaft by a ring fixed to the shaft and formed with axially
facing teeth biased into engagement with a similar ring of teeth on an annular anvil
member which is mounted to yield in an axial direction characterised in that the anvil
is mounted to yield by means of a coupling comprising a number of axially extending
springs surrounding and guided by pins located in corresponding counter bores, one
part of the coupling being fixed to the housing and the other being fixed to or formed
in the anvil member, whereby to prevent rotation of the anvil member.
2. A power operated drill according to claim 1 in which the pins are fixed to the
housing and the counter bores are formed in the anvil member.
3. A power operated drill according to claim 2 in which the pins extend from a ring
fixed to the housing of the drill.
4. A power operated drill according to claim 1 or claim 2 in which there are three,
substantially equi-angularly spaced springs and associated pins and counter bores.
5. A power operated drill according to claim 1 in which the coupling is substantially
as described and as illustrated with reference to the accompanying drawing.
