Tool for repairing damaged threads

Abstract: The invention provides a chasing tool for repairing damaged internal threads, including a body (2) provided with a bore (4); a handle (6) retained in the bore (4) with one degree of freedom in rotation, the handle (6) being provided over at least part of its length with an internal thread; a cylindrical component having an external thread matching the internal thread of the handle; a tubular member (18) fixedly attached to the body (2) perpendicular to the axis of rotation of the handle (6) and opening into the bore (4) of the body (2) and a lever (16) tiltable about a pivot (34) providing the lever (16) with one degree of freedom in rotation, the cylindrical component being articulated to the lever (16) and a cutter (28) articulated to the other end of the lever (16), the cutter (28) projecting from the tubular member (18). In another embodiment, there is provided a chasing tool for repairing damaged internal threads, including a bar (46); a first arm (50) fixedly attachable to the bar (46) and extending perpendicular to the bar; a second arm (54), co-planar with the first arm (50) and slidable along the bar (46); means for immobilizing the second arm along the bar, and at least one cutter (68) articulated to the second arm.

Description: Field of the Invention The present invention relates to a chasing tool for repairing damaged internal threads. Background of the Invention Internal threads, although better protected against mechanical damage than external threads, are frequently damaged by jamming, due to forcible introduction of male components which either have a different pitch, or were misaligned. Also, there often arises the need to remove scale, rust or other encrustations. U.S. Patent 5,281,059 relates to a tool for repairing damaged threads in a blind hole, including an elongated body having and end with an expandable, fluted top and a second end defining a butterfly handle. The tool also includes an arbor with a forcing cone for expanding the fluted top into engagement with undamaged threads. The tool is then screwed out to reform the damaged threads. WO-A-88/00103 discloses a similar device for repairing damaged internal threads, having two movable body portions and operating means engaging the body portions with the internal threads. Summary of the Invention It is thus one of the objects of the present invention to provide a chasing tool for repairing internal threads that is effective, inexpensive and easily operated. According to the invention, the above object is achieved by providing a chasing tool for repairing damaged internal threads, comprising a housing; handle means for operating said tool, attached to said housing, and screw means, characterized in that said housing is of a substantially U-shaped cross-section accommodating a four-bar linkage delineating an elongated parallelogram formed of first and second oppositely located relatively short bars and first and second oppositely located relatively long bars, the first, upper, short bar being the stationary bar of said linkage and being constituted by a section of said housing, the second, lower, short bar being constituted by the center line of a cutter disposed in a mount, said relatively long first and second bars being constituted by lever-like members articulated to said short bars, and the rotation of said screw means causes said long bars to swivel relative to said stationary bar, whereby said cutter is moved relative to said housing, with the center line of said cutter maintaining its parallel position relative to said stationary linkage bar. Brief Description of the Drawings The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood. With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the drawings: Fig. 1 represents another embodiment of the chasing tool according to the invention; Fig. 2 is a view in cross-section along plane XIX-XIX of the tool of Fig. 1; Fig. 3 is an enlarged, cross-sectional view of the lower portion of the tool shown in Fig. 1; Fig. 4 is a view in cross-section along plane XXI-XXI of the enlarged tool portion of Fig. 3; Fig. 5 shows the lower portion of the tool of Fig. 1 at the middle of its range; Fig. 6 represents the tool of Fig. at the upper end of its range; Fig. 7 is a view in cross-section along plane XXIV-XXIV of the tool as represented in Fig. 23; Fig. 8 is a cross-sectional view of the tool of Fig. 1, including the attachment for increasing the upper limit of the tool's reach; Fig. 9 is a view in cross-section along plane XXVI-XXVI of the tool of Fig. 8; Fig. 10 shows the tool of Fig. 8 at the upper limit of its reach; Fig. 11 is a view in cross-section along plane XXVIII-XXVIII of the tool of Fig. 10; Fig. 12 represents yet another embodiment of the chasing tool according to the invention; Fig. 13 is a view in cross-section along plane XXX-XXX of the tool of Fig. 12; Fig. 14 is a view in cross-section along plane XXXI-XXXI of the tool of Fig. 12; Fig. 15 shows the tool of Fig. 12 in an extended position and includes an attachment for extending the upper limit of the tool's reach, and Figs. 16 and 17 iliustrate a pressure pad for use in the tools of Figs. 13 or 2 at the lower and upper ends of the ranges, respectively. Detailed Description of Preferred Embodiments Fig. 1 represents embodiment of the chasing tool according to the invention. It comprises a housing 90 of a substantially U-shaped cross-section, which is seen to better advantage in Fig. 2, in which WP stands for workpiece. Inside this housing there is located a lever or beam 92, the upper end of which is articulated to housing 90 by means of a rod 94, which projects from both sides of housing 90 and serves also as a handle whereby to rotate the tool. At the lower end of beam 92 there is seen in the enlarged drawing of Fig. 3 a cylindrical cutter 96, one end of which is constituted by the cutting edges and, the other end of which is stepped down to a smaller diameter seated with some clearance in a hoic 98 in beam 92, seen to best effect in Fig. 20. Hole 98 is the end portion of a larger hole 100 of an elongated cross-section (Fig. 4), the width of which corresponds to the diameter of cutter 96 and the height of which is somewhat larger than this diameter, so that cutter 96 can tilt within the paper plane, but not in a plane perpendicular to the paper plane. Further seen is a small radial bore 102 into which enters, with clearance and to some depth, the tip of a screw 104. It will be appreciated that screw 104 has no tightening or clamping purpose, but merely serves to prevent cutter 96 from slipping out. Returning to Figs. 1 and 2, there is seen another lever in the form of a flat steel spring 106, the upper end of which is riveted to lugs 108 raised from the wings of the U-shaped housing 90 and the lower end of which is provided with a hole 110 (Fig. 3) through which cutter 96 passes. Another hole 112 is provided at about half the spring's length. Through this hole passes the threaded shaft 113 of a thumbscrew 114, which shaft matches a threaded bore in beam 92. Assuming the shaft thread to be right-handed, by turning thumbscrew 114 in the clockwise sense, beam 92 will obviously swivel about its pivot, rod 94, in the clockwise sense, as well. One task of spring 106 is to constantly apply pressure to beam 92, to ensure that shaft 113 stays in permanent contact with the inside of housing 90. The other, more important task is fundamental to the kinematics of the device: spring 106 constitutes one bar, a , of a special case of a four-bar linkage a-b-c-d delineated in Fig. 1 by bold dash-dotted lines. Since a = c and b = d, the linkage forms a parallelogram, and if the stationary bar b, extending from the point of bend p of spring 106 to the center of pivot 94 is horizontal, bar d, passing through the centerline of cutter 96, will also be horizontal, regardless of the angle of swivel of beam 92. This is clearly seen when comparing Fig. 1, which shows the device as set for the smallest thread diameter of its range, with Figs. 5 and 6 representing the device at the middle and the upper ends of its range. In all positions, cutter 96 is seen to be horizontal. The articulation of the upper end of flat spring 106, constituting bar a of the four-bar linkage, is to be understood as being realized by the bend in the spring immcdiatcly below lugs 108 in Fig. 1. The profile of housing 90 can be seen in Fig. 2, with the curved portion abutting and pressing against the thread section opposite the spot being repaired. Along the active portion of the device (roughly the lower third), the wings of the U-shaped profile have been shortened, as clearly seen in Fig. 6, to allow the device to reach a reasonable depth. While the expansiveness of the device of Fig. 1 (i.e., the difference between the smallest and the largest internal thread diameters treatable) is a given magnitude, the upper limit, as exemplified by Fig. 6, can be increased by means of an attachment mountable on the rounded back of housing 90, as seen in Figs. 8 to 11. The accessory consists of a trough-like profile 116 of a relatively short length, soldered or brazed to a spacer 118 and fixedly mounted on the back of housing 90 by means of a screw 120. Advantageously, the position of the attachment is also secured by two dowel pins (not shown). Another embodiment of the device is seen in Figs. 12 to 15. This embodiment realizes a true four-bar linkage and comprises an attachment enabling the above-mentioned upper limit to be greatly expanded. The fixed or stationery bar is defined by two pivots 122 and 124 extending between the two wings of a housing 126 having a U-shaped profile. Their counterparts are two pivots 128, 130 whereby a block 132 is articulated to a lever 134 constituting one of the long bars of the four-bar linkage. The upper end of lever 134 is articulated to housing 126 by means of pivot 124. The second long bar of the four-bar linkage is constituted by two relatively slender levers 136 articulated to housing 126 by pivot 122 and to block 132 by pivot 128. Cutter 138 smoothly fits a bore 140 in block 132 and is secured inside bore 140 by pivot 128 passing through a bore inside cutter 138 with enough clearance to permit the cutter to adapt itself to the lead angle of the thread to be repaired. Housing 126 is provided with a head piece 142 to which is attachable a handle 144. In Fig. 12 the device is shown set to the smallest thread diameter for which the tool can be used. For larger diameters, the four-bar linkage is swung out to the required degree, as seen in the left half of Fig. 15. This is accomplished by means of a threaded bolt 146 (see also Fig. 13), the flattened end 148 of which is articulated to lever 134 by means of a pivot 150. The other end of bolt 146 passes through a cross-member 152 articulated to housing 126 and engages a knurled nut 154 articulated to cross-member 152 with only one degree of freedom in rotation. When nut 154 is rotated in the clockwise sense, bolt 146, having a right-handed thread and unable to rotate because of pivot 150, is drawn into nut 154, thereby causing the four-bar linkage to swing to the left, as seen in Fig. 15. Fig. 15 represents the device of Fig. 12, together with an attachment used to extend its reach. The attachment consists of an arm 156 mountable on handle 144 at discrete intervals determined by holes 158 associated with pegs or bolts (not shown). Further seen is a trough-like profile 160 fixedly attached to arm 156, which abuts against the threads opposite the spot to be repaired and serves as a pressure pad. An improved pressure pad is seen in Figs. 16 and 17. It has the form of an elongated, elastically deformable, very shallow trough 162, advantageously made of a piece of hardened and tempered steel sheet riveted to the U-shaped profile of housing 126 in Fig. 13, or housing 90 in Fig. 2. By flexing, trough 162 more or less adapts itself to the curvature of the inside threads, thereby spreading the working pressure over a greater length of thread crests, and thus protecting them against deformation. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims: A chasing tool for repairing damaged internal threads, comprising: a housing (90); handle means (114) for operating said tool, attached to said housing (90), and screw means (113), characterized in that said housing (90) is of a substantially U-shaped cross-section accommodating a four-bar linkage (a, b, c, d) delineating an elongated parallelogram formed of first and second oppositely located relatively short bars (b, d) and first and second oppositely located relatively long bars (a, c), the first, upper, short bar (b) being the stationary bar of said linkage and being constituted by a section of said housing (90), the second, lower, short bar (d) being constituted by the center line of a cutter (96) disposed in a mount, said relatively long first and second bars (a, c) being constituted by lever-like members (92) articulated to said short bars (b, d), and the rotation of said screw means (113) causes said long bars (a, c) to swivel relative to said stationary bar (d), whereby said cutter (96) is moved relative to said housing (90), with the center line of said cutter (96) maintaining its parallel position relative to said stationary linkage bar (b). The tool as claimed in claim 1, wherein said first lever-like member (92) is a flat-spring one end of which is fixedly clamped to the upper end of said housing (90), the other end of which is provided with a first opening (110) through which projects said cutter (96) and which constitutes the point of articulation of said first lever-like member (92), and a second opening (112) through which said screw means (113) passes. The tool as claimed in claim 1, wherein the non-cutting end of said cutter (96) is stepped down to a smaller diameter. The tool as claimed in claim 1, wherein said second lever-like member (136) is a beam one end of which is pivoted to said housing (90), the other end of which is provided with an elongated bore (100) ending in a short circular bore (98) fitting said stepped-down end of said cutter (96) with clearance, which short bore (98) constitutes the point of articulation of said second lever-like member (136). The tool as claimed in claim 1, wherein said second short bar (d) of said four-bar linkage is in the form of a block to which said first and second long bars (a, c) are articulated. The tool as claimed in claim 1, further comprising an attachment for increasing the largest thread diameter for which said tool is usable, comprising a trough-like profile (116) fixedly attached to a spacer member (118) and mountable on the back of said housing (90). The tool as claimed in claim 15 further comprising an attachment for increasing the largest thread diameter for which said tool is usable, comprising an arm (156) mountable on said handle at a distance from said tool and a trough-like profile (116) fixedly attached to said arm (156), said profile (116) abutting against the threads opposite to the spot to be repaired. The tool as claimed in claim 1, further comprising a pressure pad attachable to said housing (90), said pad being in the form of an elongated, shallow trough (162) made of an elastically deformable material.

Inventors: ABRAHAM MOSHE, STAHL ZEEV, ABRAHAM, MOSHE, STAHL, ZEEV
Applicants: SHILO TECHNOLOGIES LTD, SHILO TECHNOLOGIES LTD.
Application year: 2000
Main classification: B23G9
IPC codes: B23G9, B23G1, B21D11