Method and apparatus for registering a torque-transmitting tool in a fixture for forming a diagonal bore in the tool

A torque transmitting tool is machined by registering the torque transmitting tool using a shoulder between the shank and the out-of-round drive portion of the tool as a reference. First and second seating surfaces are milled on first and second opposed surfaces of the tool, and then first and second bores are drilled into the drive stud, starting from the first and second seating surfaces, respectively. The first and second bores intersect within the drive stud to form a stepped diagonal bore in the tool. Alternately, all machining operations are performed from one side of the tool.

BACKGROUND

The present invention relates to machining and registering methods well suited for use with torque-transmitting tools such as out-of-round drive studs.

U.S. Pat. No. 5,644,958, assigned to the assignee of the present invention, discloses a quick release mechanism for an extension bar suitable for use with a socket wrench. This quick release mechanism utilizes a diagonally-oriented, stepped bore formed in the drive stud of the extension bar.

The machining of such diagonal bores presents manufacturing difficulties. In particular, there is a need to register the drive stud reliably with respect to the drilling axis. Poor registration can result in misplaced machined surfaces, and is therefore to be avoided. Proper location of a diagonal bore is even more difficult, because the oblique orientation of such a bore can cause the bore to deviate from the desired drilling axis, either at the start of the bore or during the drilling operation. Furthermore, when a drill is passed completely through the drive stud on a diagonal axis, there is a tendency for the drill to break as it exits the drill stud. This tendency is especially great for a stepped bore, which requires a relatively smaller diameter portion at the front of the drill.

SUMMARY

The present invention is directed both to an improved system for registering a drive stud for machining, and to improved systems for forming a diagonal bore. The invention itself is defined by the following claims, and the following paragraphs of this section are intended as an introduction, not as a definition of the invention.

Preferred embodiments described below efficiently form a stepped bore in a drive stud by first registering the drive stud precisely with respect to a drilling axis with a fixture that engages the shoulder between the out-of-round, extreme end portion of the drive stud and the adjacent, shank portion of the drive stud. In some preferred embodiments, the stepped bore is drilled in two stages, using two drills of differing diameters that enter the drive stud from respective sides of the longitudinal axis. The bores formed by these drills meet in the interior of the drive stud to form the required step.

Other preferred embodiments form a first seating surface on the tool at a point of intersection between an exterior surface of the tool and a drilling axis that intersects this surface at an oblique angle. This seating surface is shaped to facilitate subsequent drilling operations. For example, the seating surface may be oriented substantially transverse to the drilling axis. This feature, along with the fixture described above, can be used in methods that form the diagonal bore exclusively from one side of the longitudinal axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now toFIGS. 1 and 2, a drilling system10incorporates a preferred embodiment of this invention. The drilling system10includes a table12that supports first and second drilling heads14,16, a fixture18, and a clamp20. The first and second drilling heads14,16support first and second drills22,24aligned with respective first and second drilling axes26,28. The first and second drilling heads14,16are rotated in the conventional manner about the respective drilling axes26,28by motors (not shown) and are moved axially along the respective drilling axes26,28by respective air cylinders (not shown).

The clamp20supports a torque-transmitting tool T in the fixture18for machining.

FIG. 3shows a cross-sectional view of the fixture18with the tool T clamped in place. As shown inFIG. 3, the tool T includes a drive stud that is made up of a shank portion S and an out-of-round drive portion D. In this embodiment, the shank portion S has a circular cross-section and the drive portion D has substantially a square cross-section. The transition between the shank S and the drive portion D comprises a shoulder R that defines a reference point at any desired point on the shoulder R.

The fixture18defines an out-of-round opening30that is shaped to receive the drive portion D, and a protruding element32that is shaped to engage the reference point on the shoulder R. Note that the opening30is deeper than the drive portion D is long such that the shoulder R registers the tool T with respect to the protruding element32, and not the end of the drive portion D.

As shown inFIG. 3, the fixture18also supports first and second drilling bushings34,36. Each of the bushings34,36is aligned with the respective drilling axis26,28and is sized to receive closely and support the respective drill22,24. Preferably the bushings34,36are formed of a hard material such as silicon carbide, and they are provided with oblique ends38,40shaped to conform closely to the respective surfaces of the tool T and thereby to provide support for the respective drills22,24to a position closely adjacent to the tool T.

FIG. 4shows a drilling system100that incorporates a second preferred embodiment of this invention. The drilling system100is similar to the drilling system10in that it includes first and second drilling heads102,104positioned as described above with respect to a fixture106. The drilling heads102,104and the fixture106can be identical to the drilling heads14,16and the fixture18described above.

In addition, the drilling system100includes first and second milling heads108,110. The first and second drilling heads102,104are arranged along a first line120, and the first and second milling heads108,110are arranged along a second line122. In this embodiment, the lines120,122intersect at an angle of about 60°.

The fixture106and the associated clamp112are mounted on a plate114that is rotatably mounted with respect to the remainder of the system100. The plate114can be rotated about the longitudinal axis L of the tool T between two positions that are separated by an angle of 180°. In the first position, the drills of the first and second drilling heads102,104are aligned with the bushings116,118, as shown inFIG. 4. In the second position (not shown), the mills of the first and second milling heads108,110are aligned with the bushings116,118(FIG. 4)FIG. 5provides a flow chart of a milling method practiced by the system100ofFIG. 4, andFIGS. 6–8provide cross-sectional views of the tool T at three successive stages of the milling process.

In block200ofFIG. 5, the tool (an extension bar in this example) is registered in the fixture. As described above, the shoulder R between the shank S and the drive portion D is used as a reference point in order precisely to position the tool in the fixture. In block202, first and second seating surfaces are milled on first and second surfaces of the drive stud. InFIG. 6, the first and second seating surfaces are indicated at242and244, respectively. As shown inFIG. 6, the seating surfaces242,244are formed in first and second surfaces246,248, respectively of the tool T. These surfaces246,248are disposed on respective sides of the longitudinal axis L, and are parallel to one another in the view ofFIG. 6. In this embodiment, the seating surfaces242,244are formed by an end mill as planar surfaces oriented at right angles to the respective drilling axes226,228. After block202the plate114is indexed to bring the fixture bushings into alignment with the drilling heads.

In alternative embodiments the seating surfaces242,244can be formed by machining operations along other axes, e.g. perpendicular to the surfaces246,248or to the axes226,228. The seating surfaces242,244may take many shapes. For example, they may be perpendicular to the axes226,228at the point of intersection with the axes226,228, but otherwise curved (e.g. spherically concave or cylindrically concave), or they may form a corner that locates a drill. In all cases, the seating surfaces242,244are shaped to reduce any tendency of the drill bit of a subsequent drilling operation to wander or skate away from the intended drilling axis, as compared with the original surfaces246,248. In some cases (e.g. the cylindrically curved or the corner surfaces described above), the seating surface will not be rotationally symmetrical about the drilling axis.

Continuing withFIG. 5, in block204a first bore is drilled from the first seating surface into the tool, and in block206, a second bore is drilled from the second seating surface into the tool to intersect the first bore.FIG. 7shows the tool T at an intermediate stage in the formation of the first and second bores250,252. Note that the first bore250has a larger diameter than the second bore252, and that the respective drilling axes226,228are co-linear.FIG. 8shows the tool T at a later stage of manufacture, at which the bores250,252have intersected to form a stepped bore that extends completely through the tool T and defines a shoulder254. Preferably, the first and second bores250,252are drilled in a manner such that the drilling operations overlap in time to reduce the total time required to form the stepped bore. As shown inFIG. 8, the angle α1between the first surface246and the first drilling axis26is equal to the angle α2between the second surface248and the second drilling axis28. The angles α1and α2are both oblique angles. If desired, either bore250,252can be drilled before the other.

Continuing withFIG. 5, the extension bar is then removed from the fixture in block208.

FIG. 9relates to another preferred method of this invention. The method ofFIG. 9can be used to drill a stepped bore similar to the bore shown inFIG. 8, but in the method ofFIG. 9all drilling and milling operations proceed from only a single side of the tool being formed.

As shown in block300ofFIG. 9, a tool is first registered in a fixture. The tool can be the tool T described above, and the fixture may be identical to the fixture shown inFIG. 3. However, since all drilling operations proceed from a single side of the tool, the bushing36is not needed. As described above, the shoulder between the drive portion D and the shank S provides a preferred registration surface for the fixture.

Next, at302, a seating surface is milled on an exterior surface of the tool from side S1. The seating surface may be substantially identical to the seating surface242ofFIG. 6, and the side S1may be the surface246ofFIG. 6. At304, the seating surface is then center drilled from side S1. A center drilling operation forms a small conical recess in the seating surface to assist in centering a drill in subsequent drilling operations.

Because the seating surface formed at302in this example is substantially transverse to the drilling axis of the center drill of304, the center drill of304consistently and reliably forms the center drill recess at the desired intersection of the drilling axis and the seating surface. The drilling axis may be oriented as shown at226inFIG. 6, and the center drill recess is formed at the intersection of the drilling axis226and the seating surface242.

At306, a larger diameter drill is used to drill part of the larger bore from side S1. This drill is centered by the center drill recess formed at304. Next, at308, a smaller diameter drill is used to form part of the smaller bore, again proceeding from side S1along the drilling axis. At310, the larger bore is completed from side S1with a drill of the same diameter as that used at306. At312, a smaller drill is used to complete formation of the smaller bore from side S1. The drill used at312is the same diameter as that used at308. Finally, at314, the tool is removed from the fixture. If desired, a step drill may optionally be used between blocks312and314to provide the final finish and shape to the step between the larger and smaller bores.

The method ofFIG. 9can be implemented using a conventional, numerically controlled, indexed milling machine and the tool registration fixture described above. The registration fixture provides all of the advantages described in conjunction with the first and second embodiments, and the seating surface assists in properly locating the center drill recess.

It should be apparent from the foregoing discussion that the drilling systems described above precisely register the tool using the shoulder between the out-of-round drive portion and the shank portion of the drive stud. The drilling system10operates similarly to the drilling system100, except that no seating surfaces242,244are formed. The methods described above in conjunction with the systems10,100can readily be automated in quick and reliable systems that provide little tool breakage since the drills are well-supported to a point closely adjacent the tool, and the drills are never caused to exit the tool at an oblique angle. By using the seating surfaces242,244, consistent results can be achieved using a preferably substantially constant speed of drill advance. The registration techniques described above may be used separately from the drilling techniques, and vice-versa.

The widest variety of machine tools and mechanisms for controlling the movement of these machine tools can be used. For example, pneumatic, hydraulic, and electric power systems can be used. Conventional numerically controlled machine tool techniques can be used to automate the methods described above. In alternative embodiments of this invention, either the machine tools can be moved along any suitable direction to bring successive machine tools into alignment with the drilling axes, or the fixture can be moved along any suitable direction to achieve a similar result. Any suitable combination of rotational and/or translational movements can be used. This invention is not limited to use with the specific machine tools or the specific workpieces described above.

As used herein, the term “drive stud” is intended broadly to encompass the out-of-round portion and adjacent portions of a torque transmitting tool at intermediate stages of manufacture.

The term “oblique” is intended broadly to encompass acute angles between 0 and 90 degrees.

The term “to machine” is intended broadly to encompass any material removal method including drilling, milling, turning, grinding and electrical discharge machining, for example.

The term “machine tool” is intended broadly to encompass any tool for machining as defined above.

The term “operative position” is intended to refer to a relative position between a machine tool and a workpiece that orients the machine tool to a desired alignment with the workpiece. The operative position can be achieved by moving either the machine tool, or the fixture in which the workpiece is registered, or both to achieve the desired alignment.

The term “machined surface” is intended broadly to encompass a surface formed by any machining activity or any machine tool, including those described above.

The term “reference surface” is intended broadly to encompass a point-like surface, a line-like surface, or a surface that extends substantially in two or three dimensions.

The term “shoulder” is intended broadly as applied to a tool to encompass any part of the transitional surface between the shank portion and the drive portion of the tool, including but not limited to portions of the transitional surface immediately adjacent to the shank portion and the drive portion.

The term “fixture” is intended broadly to encompass one or more elements that stabilize the workpiece in the desired orientation. A fixture may include multiple discrete elements that are separately mounted to a reference element, and the fixture may contact the workpiece at only a few discrete points rather than receiving the workpiece as illustrated. There is no requirement that a fixture include drill bushings as shown, whether or not drill bushings are used. In some embodiments, the fixture may register a tool without physical contact with a reference surface of the tool, as for example when the position of the reference surface is sensed optically rather than by physical contact.

The foregoing detailed description has described only a few of the many forms that this invention can take. For this reason, this detailed description is intended only by way of illustration, and not by way of limitation. It is only the following claims, including all equivalents, that are intended to define the scope of this invention.