Threaded Lockwasher And Method For Fabrication Thereof

Abstract

A lockwasher having tabs and gripping edges is made of a strip of coil stock material cut and wound a plurality of turns on a mandrel. A portion of at least one turn of the washer is axially displaced so at least one edge of the displaced portion is circumferentially aligned with a shoulder of an adjoining turn for preventing unwinding of the finished product.

Parent Case Text

This application is a continuation-in-part of the presently pending U.S. Pat. application Ser. No. 703,494, entitled "Threaded Lock Washer and Method for Fabrication Thereof" filed Nov. 13, 1967, now U.S. Pat. No. 3,453,672.

Description

This invention relates to threaded lockwashers, and more particularly to threaded lockwashers having improved locking characteristics and methods and equipment for the fabrication thereof.

Threaded lockwashers, which are used in the millions each year, are essentially cylindrical bodies each having a threaded central bore and spaced gripping or biting tabs along its outer periphery. There are many uses for such washers, typical of these being the locking of a threaded pipe to an outlet box. Prior art washers have generally been fabricated by an appropriate stamping operation on sheet stock.

There are three major problems encountered in the use and fabrication of prior art lockwashers. First, in the stamping operation up to 80 percent of the stock material may be wasted because the material which is punched out to form the central bore and the rounded periphery configuration is wasted. Second, in the manufacture of the prior art lockwashers once the bore is formed it must be threaded, and the threading step is a relatively expensive one from the points of view of the initial cost of the threading equipment and the time which is required for the operation. Third, prior art lockwashers are known to often work loose after attachment to an outlet box or similar device, due primarily to the difficulty of tapping smooth 100 percent threads.

In my parent application, Ser. No. 394,160 filed Sept. 3, 1964 and entitled "Threaded Lock Washer," now U.S. Pat. No. 3,260,293 there is disclosed an improved lockwasher and a method for its construction. A strip of flat-wire material, with a beveled edge, is wound to form a helical coil. The coil is wound such that the beveled edge of the strip defines a central threaded bore. The coil may then be stamped to form the gripping tabs. This method of fabrication is advantageous for three reasons. Because the wire strips which eventually form the final lockwashers may be cut from sheet stock with very little material being wasted, a considerable savings is realized in the cost of the material. And because the beveled edge is formed on each strip before the winding operation, there is no need for the threading operation in the manufacturing process. (Additionally, a 100 percent thread is formed.) As for the final lockwasher itself it is vastly superior to the prior-art-type of lockwasher. If two turns are made in the winding operation, the final washer has the characteristics of two separate washers, one on top of the other. When the "combined" lockwasher is used in practice and tightened to an outlet box, the outer convolution rotates slightly with respect to the inner convolution which rests against the box wall. This slight rotation provides a dual-locking characteristic which in the prior art can be obtained only with the use of two separate washers. A single washer constructed as described in my above-identified application is substantially foolproof from working loose after attachment.

It has been found that electricians and other persons, when using the lockwasher disclosed in my above-identified application, are sometimes apt to ruin it. A lockwasher is generally tightened to an outlet box or other wall by placing a screwdriver against one of the gripping tabs and hitting it with a hammer. The force applied by the hammer causes the washer to turn on the threaded pipe and the gripping tabs to bite into the box wall. If an electrician follows the same procedure when using my above-described lockwasher there is no problem. However, it is possible that due to the construction of the washer an attempt will be made to tighten it in another manner. Because the washer is basically a helically wound strip of flat wire, the surface furthest away from the box wall, the surface subject to view during installation, exhibits a cut end of flat wire. An electrician is apt to place the tip of the screwdriver against this edge and strike it with a hammer to force the turning of the washer. In so doing, the helically wound wire may uncoil to too great an extent and the washer may have to be discarded.

To overcome this problem, my copending application, Ser. No. 534,837, filed Mar. 16, 1966 entitled "Threaded Lock Washer and Method of Fabrication Thereof" now U.S. Pat. No. 3,397,726, disclosed an improved lockwasher having a locking tab provided on the washer itself. This tab is a radial extension of the lower convolution and is bent upward to fit between two of the gripping tabs extending from the upper convolution. The locking tab, in the illustrative embodiment of the invention, engages the upper convolution near its end. This has the effect of rigidly attachment the end of the upper turn to that part of the wire coil beneath it. In fact, the entire upper turn is a rigid unit, and even if the upper edge of the strip is struck, the washer turns without unfurling.

Because of the locking tab, however, the manufacturing process requires more steps than merely the coiling of a wire strip followed by the stamping of it to form the gripping tabs. For example, the locking tab must be bent to engage the upper turn of the coil. And the stamping process must not destroy the tab after it is bent, if the bending step is first, or before it is bent, if the stamping step is first. Moreover, an additional punching operation may be required to form a slot on the side (interior or exterior) of the upper end of the coil into which the bent tab may fit. Thus, all things considered, the manufacturing process for constructing a helically wound lockwasher with a locking tab is considerably more complex than the process for constructing the simpler lockwasher disclosed in my above-identified application.

It is a general object of this invention to provide a lockwasher, and a method and equipment for the fabrication thereof which are improvements over those disclosed in my above-identified application.

In accordance with the principles of my invention a portion of the turns of the final coiled configuration is displaced longitudinally after being coiled on a threaded mandrel so that adjoining portions of the turns engage. This displacement may take place while a shearing punch and die forms a series of notches and gripping tabs with biting edges on the coiled strip. The displaced portion of the turns are so offset and bent that the portion of the upper turn engages the adjoining lower turn, so as to effectively rigidly attach the upper turn to the lower turn. Then, if the upper turn is struck by the user, the washer turns without unfurling. Because the upper turn is still free for relative slight movement with respect to the lower turn, the dual-locking characteristic of the lockwasher is not lost even though the upper turn is in fact a rigid unit. Thus, the offset portion ensures that the washer will not be deformed during installation by an absent-minded technician, without, however, destroying any of the beneficial characteristics of the washer.

It is a feature of this invention to provide a lockwasher having gripping tabs and a screw-threaded central bore, with a plurality of helically coiled wire strip convolutions having a portion of the turns longitudinally offset and bent for securing the upper end of the wire strip to the strip material beneath it.

Further objects, features and advantages of the invention will become apparent upon consideration of the following detailed description in conjunction with the drawing in which:

FIG. 1 is a perspective view illustrating a helical coil of flat-wire material employed to form a lockwasher in accordance with the invention disclosed in my above-identified parent application;

FIG. 2 is a perspective view of the final lockwasher constructed from the helical coil of FIG. 1, and disclosed in my above-identified parent application;

FIG. 3 is a perspective view of a final lockwasher constructed in accordance with the invention disclosed in my above-identified application;

FIG. 4 is a sectional view of the lockwasher taken along line 4--4 of FIG. 3;

FIG. 5 is a perspective view of a lockwasher constructed in accordance with the principles of the present invention;

FIG. 6 is a top plan view of the lockwasher of FIG. 5;

FIG. 6A is a bottom plan view of the lockwasher of FIG. 5;

FIG. 7 is an elevational view of the lockwasher of FIG. 5;

FIG. 8 is a sectional view of the lockwasher of FIG. 5 taken along the line 8--8 in FIG. 6.

Like numbers refer to like elements in the various embodiments.

In my above-identified application the first step in constructing the lockwasher of FIG. 2 is to form a helical coil 30 from a straight strip of stock material as shown in FIG. 1. The material is substantially rectangular in cross section, except that one lengthwise edge 31 is beveled. As the strip is wound a screw-threaded central bore is formed. The coil is then stamped or punched on a die. Notches 32 are cut out along the outer periphery of the coil. In addition, in the same step the remaining material at the periphery of the unit is bent slightly to form gripping teeth or tabs 33. The overall assembly is similar to that of the prior art. But the only wasted material is that cut out of notches 32. And because of the initial beveled edge of the wire strip 30, which strip is used to form the washer, a threading operation is not required. In addition to the advantages in the fabrication of the washer, the completed washer exhibits an unusual characteristic--it functions in practice as two separate lockwashers. As the washer is turned clockwise from above, the teeth of the lower turn of the helix grip the connecting surface, such as the wall of an outlet box. After the lower convolution stops turning the upper convolution still turns slightly if sufficient force is applied. While it may rotate only slightly with respect to the lower turn, it functions as a second lockwasher. This dual-locking characteristic is described in greater detail in my above-identified parent application.

In practice, the washer is tightened by placing the tip of a screwdriver in one of the notches 32 against the upper section of one of the gripping tabs. As the screwdriver is struck with a hammer the washer is turned. It should be noted, however, that end 34 of the metal strip is in full view at the top of the washer. An absentminded individual might mistakenly place the screwdriver against this edge rather than against one of the biting tabs. In such a case, if sufficient force is applied, after the teeth grip the outlet box wall the washer may unravel and have to be discarded.

To eliminate this possibility the improved lockwasher of the above-identified application Ser. No. 534,837 shown in FIGS. 3-4, is different from the washer of FIG. 2 in two major respects. First, end 36 in FIG. 3 is rounded rather than being straight as is end 34 in FIG. 2. (The lower end of the coil can also be rounded, although this is not as important.) With a rounded edge the installer is more likely to place his screwdriver against the biting edges. But this is not a sufficient guarantee and for this reason my improved washer includes a locking tab 35. With this tab it may not even be necessary to provide a rounded edge because the tab prevents the uncoiling of the washer even if the upper end of the helix is struck.

While the six notches of the washer of FIG. 2 are formed by punching through the entire coil at six sections on its periphery, in the washer of FIG. 3 only five of these notches are formed. The sixth notch is similar to the other five only in that the upper turn of the wire strip is cut through. The material in the lower turn directly beneath the half-notch is not cut out. Instead, it is bent up into the notch (slot) in the upper turn, as shown in FIG. 4. Thus, the upper end of the coil is in effect locked to the material directly underneath it and cannot unravel if it is struck at its end 36.

Although the construction of this washer is easily understood it is readily apparent that the method for making it is considerably more complex than that required for fabricating the washer of FIG. 2. After the wire strip is wound it is not sufficient to provide a single punching operation. The problem arises with the notch in the upper turn near edge 36. While this notch must be cut out, the material below it, which forms locking tab 35, must not be cut out. It is difficult to build a punch which will form five full notches 32 and an additional half-notch. Moreover, even after the half-notch is formed a punching operation is required to form the locking tab 35 itself. This requires a separate operation as taught in the prior application.

To avoid the complex method of producing the lockwasher shown in FIGS. 3 and 4 and yet produce a rigid lockwasher, which will not unravel, even if end 34 is struck inadvertently, the improved lockwasher of the present invention is shown in FIGS. 5-8, and differs from the washers of FIGS. 2 and 3 by displacing a portion 100 of the turns axially or longitudinally and bending the ends of this portion, so that at least one end 102 of the top turn of this portion is aligned with the bottom turn of the washer adjacent this displaced portion, indicated at 104. Because the top turn is then rigidly attached to the bottom turn, end 34 may be straight as in the lockwasher of FIG. 2. However, the end can be rounded, as at 36 if desired, but this will require a separate punching step. The washer of FIG. 5 has five notches 32 formed by punching through the entire coil at five sections on its periphery, with portion 100 overlapping two consecutive tabs 33. All of this punching and bending is done in one operation. Opposite ends of portion 100 are bent downwardly, such as shown at 106 and 108, so that the end 102 of the top turn of portion 100 is aligned with the facing end or shoulder 104 of the bottom turn of tab 33. Thus, the upper turn of the coil is in effect locked to the material directly underneath it and the coil cannot unravel, if it is struck at its end 34, since end 102 of the top turn of portion 100 will engage shoulder 104 of the bottom turn. The washer still exhibits the dual-locking characteristic. The upper washer is a rigid unit which can be viewed best by following the helix of FIG. 1 from end 34 all the way around to approximately that part indicated at 38. The second washer extends from this point to the lower end of the helical strip. These two washers can move slightly relative to each other. FIGS. 6, 6A and 7, show three different views of the washer. In FIGS. 7 and 8 a considerable space is shown between the coil layers. In construction, this dimension would be minimal but it is shown exaggerated in the drawing for the sake of clarity.

Claims

What I claim is:

1. A threaded lockwasher, comprising a plurality of turns of continuous lengthwise material forming a helix having a central opening, said turns being wound side by side in accordance with a screw thread convolution, said turns abutting each other, the lengthwise edge of the material forming the bore of said central opening having a beveled V-shaped edge to provide a screw thread along said opening, a series of tabs extending radially outward from the outer periphery of said turns and being extended down past the lowest one of said turns to provide biting edges at an angle with respect to a plane perpendicular to the axis of said central opening, and a generally inverted V-shaped portion of the periphery of one of said turns displaced axially so that opposite ends of the V-shaped portion are in general circumferential alignment with shoulders on an adjoining turn.

2. A lockwasher, comprising a plurality of turns of continuous lengthwise material forming a helix having a central opening, said opening including screw thread means said turns being wound side by side in accordance with a screw thread convolution, said turns abutting each other, a series of toothed serrations extending radially from the outer periphery of said turns, each of said toothed serrations having an abutment for causing the lockwasher to turn around a cylindrical member when struck thereat, and a generally inverted V-shaped portion of the periphery of one of said turns displaced axially so that opposite ends of the V-shaped portion are in generally circumferential alignment with shoulders on an adjoining turn.

3. A threaded lockwasher, comprising a plurality of turns of continuous lengthwise material forming a helix having a central opening, said turns being wound side by side in accordance with a screw thread convolution, said turns abutting each other, the lengthwise edge of the material forming the bore of said central opening having a beveled V-shaped edge to provide a screw thread along said opening, a series of tabs extending radially outward from the outer periphery of said turns and being extended down past the lower surface of its corresponding turn to provide biting edges at an angle with respect to a plane perpendicular to the axis of said central opening, the biting edges on the series of tabs on the lowest turn projecting axially beyond said lowest turn of said helix and each of said tabs includes a tool-striking edge, a portion of the periphery of said upper turn displaced axially into generally circumferential alignment with a lower one of said turns and a portion of said lower turn superposed with the displaced portion of said upper turn being correspondingly axially displaced and projecting beyond the lower turn.

4. A threaded lockwasher in accordance with claim 3, wherein said displaced portions of said upper and lower turns are in the form of an inverted V-shaped portion.

5. A lockwasher, comprising a plurality of turns of continuous lengthwise material forming a helix having a central opening, said turns being wound side by side in accordance with a screw thread convolution, said turns abutting each other, the lengthwise edge of the material forming the bore of said central opening having a screw thread along said opening, a series of toothed serrations extending radially from the outer periphery of said turns, each of said toothed serrations having an abutment for causing the lockwasher to turn around a cylindrical member when struck thereat, and a portion of the upper turn displaced axially into generally circumferential alignment with the lower one of said turns, and a portion of said lower turn superposed with the displaced portion of said upper turn displaced axially and projecting beyond the lower turn.

6. A lockwasher in accordance with claim 5, wherein the displaced portions of said turns are in the form of an inverted V.

7. A lockwasher in accordance with claim 6, wherein opposite ends of said portions have opposite tapers.