Conductor Wrapping Bit And Method For Forming A Surface Thereon

Abstract

A rotary bit for wrapping conductor wire about a terminal in helical convolutions to form an electrical connection. The bit includes a longitudinal terminal-receiving bore and a conductor wire-receiving groove in radially offset parallelism therewith. A wire-camming surface slopes radially inwardly from the transverse end face of the bit to the terminal bore and includes a helical rise for continuously camming and supporting a major portion of successive wire convolutions. A wire guide surface intersects the conductor groove and sloped camming surface for feeding the wire into camming position. The sloped camming surface is formed by a rotary form machining tool which is simultaneously rotated relative to the bit longitudinal axis and axially moved relative to the bit end face.

Description

BACKGROUND OF THE INVENTION

Conductor-wrapping tools commonly incorporate a bit which is connected with a rotary motor and journaled in a surrounding stationary sleeve. The bit is usually provided with a longitudinal bore for receiving an electrical terminal and a radially offset groove for receiving a stripped end portion of a wire which is to be wound in helical convolutions about the terminal upon rotation of the bit.

Known conductor-wrapping bits include types having surfaces opening to the end face of the bit which operate to cam portions of the conductor wire radially inwardly onto the terminal as the winding process is carried out. This camming action enhances the electrical and mechanical integrity of the connection in various ways. Conductor-wrapping bits known in the art which have sloped camming surfaces are disclosed in U.S. Pat. No. 2,758,797 to E. P. Miklau and U.S. Pat. No. 3,078,052 to W. L. Olds et al. The conductor-wrapping bit of Miklau provides a helical sloped surface for camming the end portion of the wire, and the wrapping bit of Olds provides a sloped surface for radial and axial camming of portions of each wire convolution as well as the end portion.

A longstanding problem in the art of conductor-wrapping bits has been the provision of a bit which will compensate for dimensional variations of the terminal and wire to provide the proper amount of camming action to assure consistency of the mechanical and electrical characteristics of connections. The criticality of providing the structural essentials for a satisfactory wrapped electrical connection is discussed in detail in U.S. Pat. No. 2,759,166 to R. F. Mallina.

Another problem in the art of wrapping bit design is the provision of adequate contact area between the bit surface and the conductor so that wear producing unit pressures between the bit surface and the conductor may be held within reasonable limits. This problem has been substantially solved with the improved wrapping bit disclosed in U.S. Pat. No. 3,531,056 issued to applicants on Sept. 29, 1970. Ser. No. 683,631 filed by applicants on Nov. 16, 1967. However, the wrapping bit disclosed in Ser. No. 683,631 does not compensate for dimensional variations encountered in mass produced terminals and conductor wire.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a conductor-wrapping bit which operates to wrap a conductor wire in successive helical convolutions about a terminal with consistency of mechanical and electrical characteristics regardless of dimensional variations which are normally encountered in mass produced terminals and wire. The present invention further provides a wrapping bit having a wire camming and support surface which operates to cam a major portion of a wire convolution radially inwardly with respect to the bit axis of rotation and axially forwardly away from the bit end face to assure a properly wrapped connection. By engaging and supporting a major portion of a wire convolution, unit pressure between the bit and wire is reduced; and, accordingly, lateral deflection of the terminal is reduced.

The functional advantages of the present invention are realized in the wrapping operation by a wrapping bit having a camming surface which substantially surrounds the terminal receiving bore and slopes radially inwardly from the transverse end face of the bit to the terminal-receiving bore whereby the wire is cammed onto the terminal over a major portion of each convolution regardless of dimensional variations in terminal and wire cross section. Furthermore, the bit camming surface is provided with a helical rise conforming substantially to the natural helix of a wire convolution to provide for reduced contact stress between the bit surface and the wire and to provide uniform camming action. The present invention further includes a wire guide surface intersecting the conductor receiving groove and the sloped camming surface which is operable to feed the wire into the most desirable camming position between the terminal edge and the bit camming surface.

The present invention also provides a novel method for forming a helical sloped surface on a conductor-wrapping bit by simultaneously providing relative axial movement between the bit and a form machining tool and rotating the tool relative to the bit about the longitudinal axis of the latter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation, partly in section, of a rotary tool which includes a wrapping bit in accordance with the present invention.

FIG. 2 is a transverse end view of the conductor-wrapping bit of the present invention.

FIG. 3 is a section view taken along the line 3--3 of FIG. 2.

FIG. 4 is a longitudinal section view taken along the line 4--4 of FIG. 2 with a terminal in position and illustrating how the helical-camming surface supports a wire convolution.

FIG. 5 is a partial longitudinal section view of the wrapping bit illustrating how the wire-camming surface compensates for variations in terminal dimensions.

FIG. 6 is a transverse end view of the wrapping bit in the process of wrapping a conductor wire about a square terminal.

FIG. 7 is a section view taken along the line 7--7 of FIG. 6.

FIG. 8 is a section view taken along the line 8--8 of FIG. 2 and showing a form machining tool in position to form the bit camming surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is operable to be used in a variety of tools commonly used in the art of making solderless wrapped electrical connections including hand-held tools and automatic machines. A typical hand-held or portable conductor wire wrapping tool is illustrated in FIG. 1 and generally designated by the numeral 10. The tool 10 includes a casing 12 and a handle 14. The casing 12 houses a suitable motor which is operated by depressing the operator trigger 16. The forward end of the tool comprises a sleeve 18 attached to the front of the casing 12 and secured thereto by a nut 20. The sleeve 18 includes a stationary collet and nut assembly 22 which is operable to removably secure an elongated tubular sleeve element 24. The tubular sleeve 24 is operable to axially retain and rotatably journal a conductor wrapping bit 26 preferably made of heat treatable steel and having a bit end face 28 opening to the distal end of the sleeve 24. The bit 26 includes an integral shank 30 having a portion nonrotatably engaged with a rotatable spindle 32 by means of a transverse pin 34. The spindle 32 is suitably rotatably driven by the tool motor whereby the bit 26 is rotated within the stationary supporting sleeve 24. In a manner well known, the conductor wire wrapping bit 26 is operable to tightly wrap the stripped end of a flexible electrical conductor wire about a metallic post or terminal in a series of helical convolutions to form a solderless electrical connection. The particular geometry of the bit end face and surfaces in proximity thereto which comprise an improvement in the art of wire-wrapping bits is set forth herein.

Referring to FIG. 2, a central cylindrical bore 36 opens to the transverse end face 28 of the bit 26 and is operable to receive a substantially square cross section terminal 38 (see FIG. 6) in place therein. The bore 36 extends a sufficient depth into the bit 26 to receive enough length of the terminal to wrap a plurality of convolutions of conductor wire thereon as will be described. Disposed about the bore 36 and intersecting the bit end face 28 is a conductor wire camming and support surface 40 which slopes radially inwardly with respect to the longitudinal bit axis 42 from the end face 28 to the intersection with the terminal-receiving bore 36. As viewed in FIG. 2, the surface 40 is formed to have a helical advance in a clockwise direction around the bore 36. That is, a point at a constant radius from the longitudinal axis 42 of the bit 26 and lying on the surface 40 would follow a helical path with respect to said axis if rotated in a clockwise manner.

Also opening to the end face 28 is a conductor wire receiving groove 44 comprising a rectangular slot 46 longitudinally formed near the circumference of the bit and closed by the inner wall 48 of the stationary support sleeve 24 (FIG. 6). An enlarged circular counterbore portion 50 of the wire-receiving groove 44 (see FIG. 7) is provided for receiving a portion of conductor wire insulation if it is desired to form a wrapped connection having an insulated portion.

Referring to FIGS. 2 and 3, the bit 26 is further provided with wire-guiding surface means 52 intersecting the wire-camming surface 40 and the wire-receiving groove 44. The guiding surface 52 slopes axially with respect to the longitudinal bit axis 42 (FIG. 3) from the intersection with the camming surface 40 to the groove 44. As may be seen in FIG. 3 the intersection of the surface 52 with the groove 44 is formed by a radius R over which a conductor wire is bent as it moves from the groove 44 along the surface 52 and into the camming position at 54 on the camming surface 40. As shown in FIGS. 2 and 3 the guide surface 52 is generally funnel-shaped converging from the intersection with the groove 44 to the intersection with the camming surface 40. The longitudinal axis of the funnel-shaped surface 52 corresponds to the line 3--3 and lies in a plane parallel to the longitudinal axis 42 of the bit. A preferred method of forming the guide surface 52 is by means of a rotary form milling cutter. Surrounding the conductor wire receiving groove 44 is a somewhat U-shaped recess 58 which is formed to facilitate a coining operation which forms the radius R.

As previously mentioned, the operation of a conductor wire wrapping bit is for the purpose of forming a series of contiguous convolutions of wire wrapped tightly on a terminal. Superior wrapped connections are performed by bits which cam the wire onto the terminal rather than merely pulling the wire around the terminal. Referring to FIGS. 6 and 7, the views show the terminal 38 wrapped with approximately two turns or convolutions of conductor wire C. However, in commencing a wrapping operation, the stripped end portion 60 of the conductor wire is inserted in the groove 44 and the wire is laid in the notch 62 in the stationary sleeve 24, see FIG. 6. Usually the insulated portion 64 of the wire C extends just inside the notch as shown. The tool 10 is then positioned over the terminal 38 with the terminal extending into the bore 36 as shown in FIG. 7. With the wire C held stationary relative to the sleeve 24 at the notch 62, the tool is operated to rotate the bit 26 in the direction of the arrow in FIG. 6. At the beginning of the wrapping operation the conductor wire is pulled out of the groove 44 and guided by the funnel-shaped guide surface 52 to a position between the camming surface 40 and the corner 66 of the terminal 38, see FIG. 6, whereby the wire is cammed by the surface 40 into contact with the terminal. As shown in FIG. 6, there is actually penetration of the terminal corner 66 into the wire C to assure adequate electrical contact area and a gastight connection. Continued rotation of the bit 26 causes successive portions of the camming surface 40 to come into camming and supporting contact with the wire C to wrap a series of helical convolutions.

A distinct advantage of the bit 26 is the provision of the helically sloped camming and support surface 40 which compressively embraces a major portion of a wire convolution whereby the wire is continuously and substantially evenly pressed radially inward against the terminal 38 and axially against the previous convolution to provide a connection of superior mechanical and electrical character. As can be seen in FIG. 4, by providing a helical advance or lead to the camming surface 40 substantially corresponding to the natural lead of a wire convolution 68 the camming surface provides continuous and even force against the wire as indicated by the force vectors 70 shown with their axial and radial components. By providing support over a major portion of the periphery of a wire convolution there is virtually no tendency for the longitudinal bit axis 42 to wobble relative to the terminal 38 and hence no tendency to bend or deflect the terminal. This reduction of unbalanced lateral forces between the bit and terminal is enhanced by the coincident position of the terminal receiving bore axis and the bit rotation axis 42.

A principal advantage of the bit 26 over known conductor wire wrapping bits is illustrated in FIG. 5. The sloping cam surface 40 is operable to compensate for terminal diagonal dimensional variations which affect the radial location of the terminal corners 66. If an undersize or lower dimensional limit terminal is encountered, the conductor wire C is guided by the funnel-shaped surface 52 onto the camming surface deeper in the recess formed by the surface 40 or further away from the transverse end face 28 whereby it is properly cammed onto the edge 66. If a terminal 39, designated by the dashed line, having the larger or maximum diagonal dimension is encountered the conductor, represented by the dashed circle, comes into camming position on the surface 40 closer to the transverse end face 28. Compensation for dimensional tolerances in wire diameter is also provided by the geometry of the cam surface 40. Not only does the sloping cam surface 40 compensate for wire and terminal dimensional variations, but the guide surface 52 provides for guiding the wire onto the camming surface at various positions by permitting the wire to leave the funnel-shaped surface at either a deep or shallow point with respect to the convergence of the surface 52 with the camming surface 40.

The bit 26 is particularly advantageously used with wire diameter of 0.010 inches or less wherein terminals have diagonal dimensions of 0.030 inches or less. Tolerances encountered in manufacturing terminals and conductor wire with these minuscule dimensions become a significant portion of the total dimension, and it may be appreciated from the foregoing that a bit in accordance with the present invention operates to compensate for the imperfections of mass produced terminals and wire.

As previously mentioned, the bit-camming surface 40 slopes radially inwardly from intersection with the transverse end face 28 to intersection with the longitudinal terminal-receiving bore 36 and the surface 40 also has a helical rise with respect to the longitudinal bit axis 42. Referring to FIG. 8, a preferred method of forming the surface 40 is by means of a rotary form machining tool 76. The tool 76 may be a milling cutter or a grinding tool or any suitable tool on which a form surface 78 may be provided. The tool 76 is rotatable about an axis 80 and is rotatably driven by the shank portion 82 which is operative to be driven by a drive spindle, not shown.

In the operation of forming the surface 40 on the bit 26, the tool 76 is positioned with its rotative axis 80 a predetermined radial distance r from the bit longitudinal axis 42 and parallel thereto. The tool 76 is then moved relatively toward the bit to penetrate the end face 28 and form the deepest portion of the surface 40, which is at the intersection of the surface 40 with the funnel-shaped guide surface 52, see FIG. 2. With the tool 76 rotating about its axis 80, simultaneously, and at a constant rate, the tool is rotated about the axis 42 with the axis 80 at the radial distance r and axially is moved with respect to the end face 28 to form the surface 40 having a helical lead corresponding to the natural lead of a wire convolution. Reversely, the bit may be orbited around the axis 80 of the tool and moved axially with respect to the tool-machining surface 78 to form the surface 40 the result in either process being to effect relative motion between the bit and the tool which will generate the sloped helical surface.

Claims

What is claimed is:

1. A bit for wrapping a wire about a terminal in helical convolutions comprising:

a. a bit end face;

b. a terminal-receiving bore in said end face;

c. a wire-receiving groove opening to said end face;

d. a helically sloped wire camming surface disposed about said terminal-receiving bore; and,

e. surface means intersecting said wire-receiving groove and said wire-camming surface and sloping axially with respect to the longitudinal axis of said bit from said intersection with said wire-camming surface to said intersection with said wire receiving groove, said surface means including a substantially funnel-shaped section converging from said intersection with said wire-receiving groove to said intersection with said wire-comming surface; for guiding said wire into a position for camming said wire onto said terminal by said wire-camming surface.

2. The invention set forth in claim 1 wherein:

the longitudinal axis of said funnel-shaped section lies in a plane parallel to the longitudinal axis of said bit.

3. In a bit for wrapping a wire about a terminal in helical convolutions:

a. a bit end face;

b. a terminal-receiving bore in said end face;

c. a wire-receiving groove opening to said end face; and,

d. a wire camming and support surface disposed about said terminal-receiving bore and sloping radially inwardly with respect to the longitudinal axis of said bit, said camming and support surface having a helical lead corresponding substantially to the lead of a wire convolution for compressively embracing a major portion of the periphery of a wire convolution and pressing said wire convolution radially against said terminal.

4. A bit for wrapping a wire about a terminal in helical convolutions comprising:

a. a bit end face;

b. a terminal-receiving bore in said end face;

c. a wire-receiving groove opening to said end face;

d. surface means on said bit for camming said wire onto said terminal; and,

e. wire guide surface means intersecting said wire-receiving groove and sloping axially toward said bit end face for guiding said wire into a position for camming said wire onto said terminal by said wire-camming surface means, said wire guide surface means comprising a substantially funnel-shaped portion converging from said intersection with said wire-receiving groove toward said bit end face.