Abstract:
A drilling apparatus capable of having a minimal axial length to permit its use within limited confines. The drilling apparatus includes a housing with a housing bore and a first housing end, a spindle rotatably supported within the housing bore, bearing elements within the housing bore and surrounding the spindle to rotatably support the spindle within the housing, and a drive unit for rotating the spindle. The spindle is configured to secure a shank of a drill bit at a first end thereof exposed at the first housing end, and the drive unit is transversely offset from an axis of rotation of the spindle.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to drilling equipment, and more particularly to a drilling apparatus capable of having a minimal axial length to permit its use within limited confines. 
     The axial length of a drilling apparatus along the axis of its drill bit can at times exceed the space available for some drilling applications. For example, the inlet pipes of steam turbine nozzle boxes may be on the order of about six inches (about 15 cm), which severely limits the size of the drilling equipment that can be placed between inlet pipe pairs for the purpose of drilling holes in their opposing parallel faces. While various small pneumatic, hydraulic and electric drills have been developed that are sufficiently small to fit between steam turbine inlet pipes, they typically lack the power, speed and/or thrust force required to accomplish the drilling operation due to the hardness of the inlet pipe material. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides a drilling apparatus capable of having a minimal axial length to permit its use within limited confines. 
     According to a first aspect of the invention, the drilling apparatus includes a housing comprising a housing bore and a first housing end, a spindle rotatably supported within the housing bore, bearing means within the housing bore and surrounding the spindle so as to rotatably support the spindle within the housing, and drive means for rotating the spindle. The spindle comprises means for securing a shank of a drill bit at a first end thereof exposed at the first housing end, and the drive means is transversely offset from an axis of rotation of the spindle. 
     The construction of the drilling apparatus allows for the drilling of holes in confined locations as a result of the manner in which the spindle is supported around its circumference and the drive means is transverse offset from the spindle, which in combination minimizes the length of the drilling apparatus along the spindle axis and, therefore, the rotational axis of a drill bit mounted in the spindle. The drilling apparatus also permits the use of a relative short drill bit, with a sufficient portion of the bit being supported by the spindle to contribute sufficient strength and stiffness to the drill bit and spindle assembly for drilling hard materials. The manner in which the spindle is supported and the transverse offset of the drive means also enables the drill bit to be rotated at sufficient rotational speeds and power levels to accomplish drilling of hard materials, including metal alloys of the type used to form steam nozzle inlet pipes of steam turbines. 
     Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a drilling apparatus in accordance with an embodiment of this invention. 
         FIGS. 2 and 3  are two opposing perspective views showing the apparatus of  FIG. 1  mounted between two steam nozzle inlet pipes of a steam turbine. 
         FIGS. 4 and 5  are two opposing side views showing the apparatus mounted between the two steam nozzle inlet pipes of  FIGS. 2 and 3 . 
         FIG. 6  is a top view of the apparatus mounted between the two steam nozzle inlet pipes of  FIGS. 2 through 5 . 
         FIG. 7  is a cross-sectional view of the drilling apparatus along line  7 - 7  of  FIG. 6 . 
         FIG. 8  shows a subassembly of the apparatus of  FIG. 1  installed between the two steam nozzle inlet pipes in preparation for installing the remainder of the apparatus and completing the assembly shown in  FIGS. 2 through 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts a drilling apparatus  10  capable of drilling holes in confined locations that prevent the use of conventional drilling equipment. As an example,  FIGS. 2 through 8  shows the drilling apparatus  10  between a pair of steam nozzle inlet pipes  12  of a steam turbine and oriented for drilling into a surface  14  of one of the pipes  12 . The spacing between the pipes  12  can be as little as six inches (about 15 cm) or less, which precludes the use of common drilling equipment when attempting to drill into either of the pipe surfaces  14  between the pipes  12 . While the drilling apparatus  10  of this invention is particularly suitable for the application represented in  FIGS. 2 through 8 , it should be evident that the apparatus  10  is versatile and capable of use in a wide variety of applications, all of which are within the scope of this invention. 
     The embodiment of the drilling apparatus  10  shown in  FIGS. 1 through 8  is represented as comprising a spindle housing  16  within which a spindle  18  is rotatably mounted with bearings  20 . The spindle  18  is shown as fitting radially within the inner races of two bearings  20 , such that each bearing  20  circumferentially surrounds the spindle  18 . The housing  16  has oppositely-disposed first and second ends  22  and  24  and a bore  26  therebetween. The bore  26  is shown closed by a plate  28  at the first end  22  of the housing  16 , allowing for the spindle  18  and bearings  20  to be installed and removed from the bore  26  through an opening  23  at the first end  22  of the housing  16 . The spindle  18  is mounted within the bore  26  so that its axis of rotation  30  coincides with the longitudinal axis of the bore  26 . The spindle  18  has a first end  32  at which an opening  36  is defined by a bore  38  within the spindle  18 , and a second end  34  that projects through an opening  25  at the second end  24  of the housing  16 . Shaft seals  27  are provided within the plate  28  and at the second end  24  of the housing  16  to enable a lubricant to be sealed within the bore  26 . 
     The spindle  18  is adapted to secure a drill bit  40  from the end  32  of the spindle  18  exposed at the first end  22  of the housing  16 . While the bit  40  could be coupled to the spindle  18  in accordance with various known techniques, the bit  40  is preferably mounted to the spindle  18  by placing and securing its shank within the spindle bore  38 . The bit  40  is preferably secured by a tapered shape defined by the bore  38 , for example, a #1 Morse taper, though other tapers and other means for securing the drill bit  40  are foreseeable and within the scope of the invention. As known in the art, a Morse taper (as well as other types of machine tapers) permits the drill bit  40  to be slipped into the spindle  18  and utilize the pressure of the drill bit  40  against the workpiece (e.g., the inlet pipe  12 ) being drilled to secure the bit  40  within the spindle  18  through friction between the tapered spindle bore  38  and the shank of the bit  40 , which preferably has a complementary taper, instead of relying on splines or keys to transmit torque from the spindle  18  to the drill bit  40 . 
     The bearings  20  supporting the spindle  18  within the housing  16  must have sufficient capacity to support loads imposed on the spindle  18  at rotational speeds required for the drilling operation. In the configuration shown in  FIG. 7 , the bearings  20  also support axial loads imposed on the spindle  18 . For this purpose, the bearings  20  are placed on either side of an annular flange  42  that protrudes from the circumference of the spindle  18  and abuts the inner races of the bearings  20 . Various bearings capable of performing in this manner are commercially available, an example being TIMKEN 05185 tapered roller bearings (or an equivalent) commercially available from the Timken Company. 
     The spindle  18  is shown in  FIG. 7  as having a transverse slot  44  adjacent its second end  34  and outside the housing  16 . The slot  44  intersects the spindle bore  38  to allows access to the end of the otherwise blind bore  38 , and serves as a knockout cross-hole to facilitate removal of the drill bit  40 . The bit  40  can be configured to have a tang  46  that protrudes into the slot  44  when the bit  40  is fully inserted and secured within the spindle bore  38 . A particular aspect of the invention is that, as seen in  FIG. 7 , the bearings  20  are axially positioned on the spindle  18  such that the tapered bore  38  of the spindle  18  extends entirely through the bearings  20 . With this configuration, the slot  44  serving as a knockout hole to the bore  38  and drill bit  40  is axially beyond the bearings  20  and located outside the housing  16  and opposite the opening  36  in the spindle  18  through which the drill bit  40  is inserted. In effect, the bearings  20  centrally support the spindle  18  to allow access to both ends  32  and  34  of the spindle  18 . 
     The spindle  18  is driven (rotated) within the housing  16  by a drive system transversely offset from the spindle axis  30 . In the embodiment shown in the figures, a suitable drive system is represented as a pulley system comprising two sheaves  48  and  52 , a drive belt  50 , and a motor  54 . The sheave  48  can be coupled to the second end  34  of the spindle  18 , for example, by press-fitting, keying, or any other suitable manner. In turn, the drive belt  50  is driven by the sheave  52  mounted on the motor  54 , whose drive axis is approximately parallel to the spindle axis  30 . A guard (not shown) of any suitable configuration may be used to protectively enclose the belt  50  and sheaves  48  and  52 . The motor  54  can be of any suitable type capable of delivering the desired levels and ranges of torques and speeds to the spindle  18  through the selected ratio of the sheaves  48  and  52 . As a nonlimiting example, a suitable motor  54  is a hydraulic motor having a variable speed capability of about 80 to about 474 rpms, and a power rating of about 0.4 to about 4 hp (about 0.3 to about 3 kW). While the spindle  18  is belt-driven in the figures, other systems for driving the spindle  18  are also within the scope of the invention, including gear systems. 
     The motor  54  is coupled to the housing  16  with a beam  56  that, as seen in  FIGS. 1 ,  2  and  6 , can be configured to promote rigidity and strength while minimizing weight. The beam  56  orients the motor  54  so that the motor drive axis is parallel to the spindle axis  30  and the drill bit  40  mounted therein. As such, the axis of the motor  54  is not in line with the spindle axis  30 , as is the case with conventional drilling equipment. 
     The housing  16 , its internal components, the motor  54 , and its drive components are represented as being supported from a mounting plate  58 . The mounting plate  58  is oriented transverse to the spindle axis  30 , and is shown in  FIGS. 1 through 7  as approximately perpendicular to the spindle axis  30 , though a perpendicular orientation is not required. As shown in  FIGS. 2 through 6 , the mounting plate  58  is shown secured to the inlet pipe  12  with straps  60 , though other means of securing the plate  58  to an object are also foreseeable and within the scope of this invention. From  FIGS. 2 through 6 , it can be seen that the plate  58  and straps  60  are adapted to secure and orient the drilling apparatus  10  to the inlet pipe  12  (or another workpiece structure) so that the first end  22  of the housing  16  and the opening  36  in the spindle  18  through which the drill bit  40  is received face away from the pipe  12  to which the apparatus  10  is secured, and face the second inlet pipe  12  to be drilled by the apparatus  10 . 
     A strongback  62  is secured to the plate  58  opposite the pipe  12 , and extends above and approximately parallel to the spindle axis  30 . The function of the strongback  62  is to rigidly support a rack  64  with gear teeth  65  facing the spindle housing  16  and meshing with gear teeth on a pinion  66  rotatably supported within a bore  67  within the housing  16 . The axis of rotation of the pinion  66  is transverse to the spindle axis  30 , such that rotation of the pinion  66 , with its teeth meshed with the rack  64 , causes the housing  16  and its spindle  18  to move toward and away from the plate  58  in a direction approximately parallel to the spindle axis  30 . In this manner, the pinion  66  allows an operator to advance or retract the drill bit  40  relative to a workpiece being machined, such as the inlet pipe  12  opposite the pipe  12  to which the drilling apparatus  10  is attached in  FIGS. 2 through 6 . 
     The rack  64  is shown in  FIGS. 1 and 7  as being slidably disposed within a stepped channel  78  that accommodates the rack  64  as well as its teeth  65 . The rack  64  is secured to the housing  16  with a pair of rack holders  68 , and gib keys  70  provide bearing surfaces that contact the rack  64  as it translates through the channel  78  in the housing  16 . This arrangement enables the rack and pinion gear system  64  and  66  to provide a stabilizing force for the spindle  18  while in operation, as well as a mechanical advantage that resists thrusts developed during operation of the drilling apparatus  10 . This arrangement also permits the installation of the apparatus  10  as subassemblies, as represented in  FIG. 8 . In particular, the mounting plate  58 , strongback  62 , and rack  64  can first be positioned and secured to the inlet pipe  12  as shown in  FIG. 8 , after which the remainder of the apparatus  10 , including the housing  16  (and its internal components), beam  56 , and drive system  48  through  54  can be positioned and secured as a second subassembly by mating the channel  78  with the rack  64  and using the rack holders  68  to secure the rack  64  within the channel  78 . 
     Access to the pinion  66  is provided through an opening in a bushing  72  that supports the shaft of the pinion  66 . In  FIGS. 1 and 4 , a hexagonal socket  74  formed in the end of the pinion shaft serves as a drive key for the pinion  66 . An allen wrench or other suitable tool (not shown) can be engaged with the socket  74  to permit manual rotation of the pinion  66 , though other means for rotating the pinion  66  are foreseeable, including computer-controlled drive motors. 
     In view of the foregoing, the bulk of the components required to support and operate the spindle  18 , including the housing  16 , motor  54 , rack  64 , and pinion  66 , are located outboard of the bearings  20  that support the spindle  18 , instead of being inline with the spindle  18  as is the conventional practice. 
     Various materials can be used in the construction of the drilling apparatus  10 , including aluminum and steels such as carbon steels, hot rolled steels and hardenable steels, nonlimiting examples of which include ASTM A36 and AISI 4340. The design options for choosing materials to construct the apparatus  10  are well within the abilities with those of ordinary skill in the art, and therefore are not described in any detail here. 
     While the invention has been described in terms of a specific embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configuration of the apparatus  10 , its individual components, and the manner in which they are assembled could differ from what is represented in the figures, and materials and processes other than those noted could be used. Therefore, the scope of the invention is to be limited only by the following claims.