Abrading – Abrading process – Drill – thread – thread cutter – reamer – or rotary cutter abrading
Reexamination Certificate
2002-04-19
2004-08-03
Nguyen, Dung Van (Department: 3723)
Abrading
Abrading process
Drill, thread, thread cutter, reamer, or rotary cutter abrading
C451S065000
Reexamination Certificate
active
06769965
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to methods and apparatus for grinding the front cutting portion or tip of twist drill bits. More particularly, the invention relates to an apparatus and method for automatically grinding or re-pointing twist drill bits that includes automatic means for removing dirt from the drill bit.
B. Description of Background Art
Printed wiring boards (PWB's) used to hold and electrically interconnect electronic circuit components are typically fabricated as laminated stacks of copper foil sheets alternating with insulating sheets made of fiberglass, the latter containing glass fibers imbedded within a solidified resin such as epoxy. Glass fibers are highly abrasive, and can quickly dull drill bits used to drill holes in a PWB for receiving component leads, or for forming passageways or vias through the PWB. A typical PWB has a thickness of about 0.062 inch, and has hundreds of holes drilled through it. Each contact with the upper surface of a PWB to drill a hole is referred to as a “hit.” Since PWB's are usually arranged in stacks of two to five boards for drilling, a corresponding number of holes are drilled for each hit. Because the abrasive nature of the PWB board materials dulls typical drill bits after about 3000-5000 holes are drilled, drill bits used for such applications must be removed from service and re-sharpened after about 1,500-2,500 hits.
In conventional drill bit grinding apparatus used to sharpen or re-point twist drill bits, the drill bit must be held in a chuck while being re-pointed. Consequently, the operator must manually perform operations such as inserting the drill into the chuck of a drill bit holder mechanism, tightening the chuck to grip the drill, positioning or aligning the drill in relation to the drill bit holding mechanism and to rotary grinding stones, advancing the drill bit towards grindstones, retracting the re-pointed drill bit from the grindstones and removing the re-pointed drill bit. Because of all of the aforementioned operations, an operator can usually operate only a single drill bit grinding apparatus at a time. Thus, even an experienced operator can typically re-point no more than about 800 to 1,000 drill bits over an eight-hour work shift. Therefore, there has been a strong demand for an automated drill bit re-pointing apparatus that has a higher throughput rate than existing re-pointing apparatuses, and which may be operated by less than highly skilled personnel. Thus, for the small twist drill bits which are used to drill holes in printed wiring boards (PWB's), equipment has been developed for re-pointing the front cutting portion of the bits including the tips, to thereby prolong the life span of bits which would otherwise have to be disposed of for not meeting dimensional tolerance requirements. Traditionally, the re-pointing process requires as an initial step removal of dirt which has inadvertently adhered to the drill bit. According to customary prior art methods, dirt is removed from a bit prior to re-pointing the bit by momentarily directing a blast of compressed air onto the surface of the bit. Next, the bit is installed in a clamping mechanism, and adjusted to a precisely pre-determined spatial position and angular orientation or phase angle of the flutes relative to abrasive grinding wheels. The grinding wheels are then brought into contact with the front cutting portion of the bit while the shank is rotated about the longitudinal axis of the bit to thereby vary the angular orientation or phase angle of the fluted portion of the bit presented to the grinding wheels. Upon completion of the grinding operation, the bit must be cleaned a second time, to remove particles of grindstone material, metal chips, or oil which may have adhered to the bit. A quality control inspection is then made of the bit to determine whether or not the bit meets pre-determined quality control criteria. Also, a ring-shaped collar is then customarily press-fitted onto the drill bit shank to identify the size of the bit and to limit its insertion depth into a workpiece.
Existing drill bit re-pointing apparatus functioning as described above experience certain problems which limit their effectiveness. For example, typical existing drill bit re-pointing methods utilize physically separated work stations to perform the various steps required in the re-pointing process. This arrangement has the disadvantage of requiring time and personnel to transport drill bits between the respective re-pointing stations, and of requiring a relatively large installation space for the various pieces of required equipment located at physically separated stations.
Moreover, in utilizing prior art methods for removing dirt from drill bits to prepare the bits for re-pointing, compressed air commonly used for dirt removal is problematic for several reasons. First, the small size of the bits and the preciseness of the re-pointing operation necessitates that the compressed air have a relative higher level of purity than normally required and supplied for typical factory production operations. Second, use of compressed air produces undesirable noise. Third, blasting dirt off a bit with compressed air causes the dirt to be scattered in an uncontrolled fashion to areas adjacent to the air gun.
In view of the problems mentioned above, the present invention was conceived to accomplish the following objectives.
OBJECTS OF THE INVENTION
An object of the present invention is to provide an automatic re-pointing apparatus and method for twist drill bits in which batches of drill bits may be re-pointed by a sequence of steps performed at a single location by an automatic re-pointing apparatus.
Another object of the invention is to provide apparatus and method for removing dirt from a drill bit to be re-pointed, by an automatic removal apparatus which does not require use of compressed air.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.
SUMMARY OF THE INVENTION
Briefly stated, the present invention comprehends an apparatus for pointing twist drill bits, the apparatus including at least one and preferably two dirt removal mechanisms.
A drill bit pointing and dust removal apparatus according to the present invention includes a drill bit processing unit which has a rotary index plate on which are mounted a plurality of circumferentially spaced apart drill bit holder units. Spaced radially apart from the periphery of the index plate are a plurality of circumferentially spaced apart, fixed drill bit processing stations where separate processing units each perform a separate processing function on an individual drill bit which has been rotated by the index plate into position adjacent to a particular station. Spaced radially apart from the periphery of the rotary pedestal are a plurality of circumferentially spaced apart operation stations where separate operation units each perform a separate operation on an individual drill bit which has been rotated by the rotary pedestal into position adjacent to a particular operation station. The loading unit includes a loading unit which has a rotary pedestal on which are located a plurality of circumferentially spaced apart transfer arms, each adapted to hold a separate drill bit. The apparatus
Chapin William L.
Nguyen Dung Van
LandOfFree
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