Abstract:
A rotary spindle  4  for a power tool such as a hammer drill is disclosed. The spindle  4  comprises a first spindle part  402  for rotation about its longitudinal an axis by means of a motor and having an inwardly directed rim  406 , and a second spindle part  404  for supporting a drill bit of the hammer drill and having an outwardly directed rim  410 . The second spindle part  404  extends through an aperture  408  in the first spindle part  402  and rims  406, 410  cooperate with each other to prevent removal of the second spindle part  404  from the first spindle part  402 . A circlip  414  locks the first and second spindle parts  402, 404  together and maintains o-rings  412  under compression.

Description:
FIELD OF THE INVENTION 
   The present invention relates to rotary spindles for power tools, and relates particularly, but not exclusively, to rotary spindles for hammer drills. The invention also relates to power tools incorporating such spindles. 
   BACKGROUND OF THE INVENTION 
   Electrically driven hammer drills are known in which a motor causes a driving member in the form of a flying mass to be reciprocally driven in a hollow spindle by means of piston, while at the same time causing the piston to rotate about its longitudinal axis. The spindle supports a working member such as a drill bit, either by direct mounting of the drill bit to the spindle, or by supporting a tool holder which in turn supports the drill bit, such that rotation of the spindle about its axis causes rotation of the drill bit to effect a drilling action, while reciprocating movement of the flying mass within the spindle imparts hammer impacts to the drill bit. 
   The spindle of a hammer drill of such known types is generally manufactured in a single piece. As a result, the entire spindle generally needs to be constructed as robustly as that part of the spindle subjected to the greatest amount of wear, even though most of the spindle does not need to be constructed to such a level of robustness. This significantly increases the cost and difficulty of manufacturing the hammer drill. Furthermore, when the hammer drill is repaired, the entire spindle generally needs to be replaced, even if only part of the spindle is damaged, which makes repair of the drill costly. 
   U.S. Pat. No. 5,373,905 discloses a hammer drill in which a spindle in which a striker mass is reciprocally driven is formed from two separate parts, i.e. a guide tube, and a tool socket arranged forwardly of the guide tube, the guide tube and tool socket overlapping each other in a certain region and being connected to each other by means of a press fit. As a result, only the tool socket needs to be formed from a robust, high-grade material, which significantly reduces the cost of manufacture and repair of the drill. 
   However, this arrangement suffers from the drawbacks that because the guide tube and tool socket are connected to each other by means of a press fit, the cooperating parts of the guide tube and tool socket must be manufactured to accurate dimensions, as a result if which manufacture of the drill is still costly. Also, the hammering action of the striker mass against the tool socket causes the tool socket to tend to detach from the guide sleeve, as a result of which components such as profiled rings securing the guide tube and tool socket together are subjected to significant stresses and can become damaged and must be frequently replaced. 
   Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a rotary spindle for a power tool, the spindle comprising:— 
   a first spindle member having at least one first abutment portion adjacent a first end thereof; 
   a second spindle member for supporting a working member of the power tool adjacent a first end thereof for rotation with said second spindle member about said axis, wherein said second spindle member is adapted to extend through an aperture adjacent said first end of said first spindle member and has at least one second abutment portion adjacent a second end thereof for cooperating with at least one said first abutment portion of said first spindle member to prevent removal of said second spindle member from said first end of said first spindle member in a first direction; 
   locking means for preventing removal of said second spindle member from said first end of said first spindle member in a second direction, opposite to said first direction; and 
   biasing means for urging said second spindle member in said second direction relative to said first spindle member. 
   By providing first and second abutment portions for preventing removal of the second spindle member from the first spindle member in a first direction, and biasing means for urging the second spindle member in a second direction, opposite to the first direction, relative to the first spindle member, this provides the advantage of minimising the tendency of impacts on the second spindle member to cause the second spindle member to become detached from the first spindle member. In addition, by providing at least one first abutment portion which cooperates with at least one second abutment portion, this provides the advantage that the first and second spindle members no longer need to fit together by means of a press fit, as a result of which the first and second spindle members do not require cooperating parts manufactured to as high a degree of accuracy as prior art devices having two-part spindles. This in turn reduces the cost of manufacture of the spindle and therefore of apparatus incorporating the spindle. 
   The first spindle member may be adapted to be rotated by a motor of the power tool. However, the spindle may be arranged such that there is no rotary movement, the power tool only impacting hammer impacts on the drill bit. 
   At least one said second abutment portion may comprise a rim extending outwardly of said axis. 
   In the case where the spindle forms part of a power tool having hammer action, for example a hammer drill, this provides the advantage of enabling direct impact of a beat piece flying mass of a hammer mechanism of the tool against the first spindle member to be avoided, which in turn minimises wear and damage to the first spindle member, thus increasing the useful lifetime of the first spindle member. 
   At least one said second abutment portion may comprise a rim extending towards said axis. 
   Said biasing means may include at least one resilient member. 
   At least one said resilient member may comprise an O-ring arranged between a said first abutment portion and a said second abutment portion. 
   Said damping means may comprise at least one compression spring. 
   Said locking means may comprise at least one removable member adapted to be mounted to said second spindle member on a side of a said first abutment portion opposite to said biasing means. 
   This provides the advantage of minimising the extent to which the or each removable member is subjected to wear by hammer impacts on the second spindle member. 
   At least one said removable member may comprise a metal clip. 
   Said first and second spindle members may comprise cooperating engaging means for preventing rotation of said second spindle member about said axis relative to said first spindle member. 
   Said cooperating engaging means may comprise a plurality of splines on one of said first and second spindle members and a plurality of grooves on the other of said first and second spindle members. 
   According to another aspect of the present invention, there is provided a power tool comprising a housing, a motor having an output shaft for actuation of a working member of the tool, and a spindle as defined above for rotation about said axis by means of said motor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:— 
       FIG. 1  is a schematic cross-sectional view of a forward part of a hammer drill embodying the present invention; and 
       FIG. 2  is a schematic cross-sectional view of a rotary spindle of the hammer drill of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a rotary hammer has a forward portion shown in cross-section, and a rear portion incorporating a motor and pistol grip rear handle in a conventional manner. Alternatively, the handle may be of the D handle type. The handle portion incorporates a trigger switch  7  for actuating an electric motor which carries a pinion (not shown) at the forward end of its armature shaft. The pinion of the motor rotatingly drives an intermediate shaft  6  via a gear which is press fit onto the rearward end of the intermediate shaft  6 . The intermediate shaft  6  is rotatably mounted in a housing  2  of the hammer via a first bearing (not shown) located at the rearward end of the intermediate shaft  6  and a forward bearing  3  located at the forward end of the intermediate shaft  6 . 
   A wobble drive hammering mechanism, of a type which will be familiar to persons skilled in the art, is provided for reciprocatingly driving a piston  24 . The piston  24  is slidably located within a hollow cylindrical spindle  4  and an O-ring seal (not shown) is mounted around the piston  24  so as to seal between the periphery of the piston  24  and the internal surface of the spindle  4 . A ram  28  is slidably mounted within the spindle  4  and an O-ring seal (not shown) is mounted around the ram  28  so as to seal between the periphery of the ram  28  and the internal surface of the spindle  4 . In this way, during normal operation of the hammer, a closed air cushion is formed between the forward face of the piston  24  and the rear face of the ram  28 , which causes the ram to be reciprocatingly driven by the piston via the closed air cushion. During normal operation of the hammer, the ram  28  repeatedly impacts a beat piece  32 , which is reciprocatingly mounted within the spindle  4 . The beat piece  32  transfers impacts from the ram  28  to a tool or bit (not shown) mounted within a forward tool holder portion of the spindle  4  by means of a tool holder arrangement  36 , of a type which will be familiar to persons skilled in the art. The tool or bit is releasably locked within the tool holder portion of the spindle  4  so as to be able to reciprocate within the tool holder portion of the spindle by a limited amount. 
   The spindle  4  is rotatably mounted in the hammer housing  2  by means of bearings  15 ,  17 . Simultaneously with, or as an alternative to, the hammering action generated by the hammering mechanism described above, the spindle  4  can be rotatingly driven by the intermediate shaft  6  as described below. Thus, as well as reciprocating, the tool or bit is rotatingly driven because it is non-rotatably mounted within the spindle  4  by the tool holder arrangement  36 . 
   An overload clutch mechanism includes a spindle drive gear  40  rotatably and axially slidably mounted on a slider sleeve  41 , and the slider sleeve  41  is non-rotatably and axially slidably mounted on the spindle  4 . The spindle drive gear  40  is formed on its periphery with a set of teeth  43 . The intermediate shaft  6  is formed at its forward end with a pinion  38  and the teeth  43  of the spindle drive gear  40  may be brought into engagement with the pinion  38  in order to transmit rotary drive to the slider sleeve  41  and thereby to the spindle  4 . The spindle drive gear  40  transmits rotary drive to the slider sleeve  41  via the overload clutch arrangement. The spindle drive gear  40  has a set of rearwardly facing teeth  40   a  formed on a rearward facing surface thereof, this set of teeth  40   a  being biased into engagement with a set of teeth formed on a forward facing surface  41   a  on an annular flange of the slider sleeve  41 . The sets of teeth are biased into engagement with each other by a spring  47  mounted on the slider sleeve  41  to extend between a washer  49  axially fixedly mounted at the forward end of the slider sleeve  41 , and a forward facing end surface of the spindle drive gear  40 . 
   The slider sleeve  41  is axially biased by means of a spring  56  into a rearward position against an elastomeric O-ring  42  mounted in a recess formed in the external surface of the spindle  4  and having an inclined surface. In the rearward position, the hammer is in a rotary mode and rotation of the intermediate shaft  6  is transmitted to the spindle  4 , provided the torque transmitted is below a threshold torque of the overload clutch. 
   The slider sleeve  41  can also be moved into a forward position against the biasing force of the spring  56  via a mode change mechanism. In the forward position, the spindle drive gear  40  is moved on the slider sleeve  41  forwardly out of engagement with the intermediate shaft pinion  38  and into engagement with a spindle lock arrangement  60 , the function of which is not relevant to the present invention and will therefore not be described in further detail. With the slider sleeve  41  and spindle drive gear  40  in a forward position, the hammer is in a non-rotary mode with the spindle  4  fixed against rotation. The mode change arrangement may comprise a mode change knob  55  rotatably mounted on the housing  2  and having an eccentric pin  57  which is engageable with the rearward face of the annular flange  41   a  of the slider sleeve  41  to move the slider sleeve forwardly. 
   In the position shown in  FIG. 1 , the spring  56  biases the slider sleeve  41  into its rearward position. However, on rotation of the mode change knob through 180 degrees from its position shown in  FIG. 1 , the eccentric pin  57  pulls the slider sleeve  41  forwardly against the biasing force of the spring  56 . The eccentric pin  57  then pulls the slider sleeve  41  forwardly to move the spindle drive gear  40  out of engagement with the pinion  38  of the intermediate shaft  6  and into engagement with the spindle lock arrangement  60 . 
   Referring now to  FIG. 2 , the spindle  4  of the apparatus of  FIG. 1  is formed as a two part spindle  4  comprising a first spindle part  402  arranged rearwardly of a second spindle part  404  for supporting beat piece  32  for imparting impacts to a drill bit (not shown). The first spindle part  402  has an inwardly directed rim  406  at a forward part thereof defining a splined aperture  408  for slidably and non-rotatably receiving second spindle part  404 . The second spindle part  404  is provided with an outwardly directed rim  410  at a rear end thereof, and a pair of rubber O-rings  412  are arranged between the flanges rims  406 ,  410 . To prevent rotation of the second spindle member about the axis relative to the first spindle member, the second spindle members may include at least one groove  403  and the first spindle member may include at least one radial spline  407  to engage the groove  403 . 
   The second spindle part  404  is made of more robust material than first spindle part  402  and is held in position relative to the first spindle part  402  by means of resilient metal circlip  414  arranged to grip second spindle part  404  in a groove  416  thereof to maintain rubber O-rings  412  under compression to prevent axial movement of second spindle part  404  relative to first spindle part  402 . 
   In order to assemble the spindle  4 , the second spindle part  404  is urged outwardly of the aperture  408  in first spindle part  402  until the rubber O rings  412  are placed under compression between the rims  406 ,  410 . The circlip  414  then secures the second spindle part  404  in position relative to the first spindle part  402 . 
   During operation of the hammer drill, the motor causes the two-part spindle  4  to rotate about its longitudinal axis, while reciprocally driving the ram  28  axially in the hollow spindle  4  to impart impacts to the beat piece  32 . The ram  28  only impacts against the second spindle part  404 , as a result of which wear and damage to the first spindle part  402  is minimised, and only the second spindle part  404  need be replaced during repair of the hammer drill. 
   It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, rubber O-rings  412  may be replaced by a compression spring.