US3397726A

US3397726A - Threaded lock washer and method for fabrication thereof

Info

Publication number: US3397726A
Application number: US534837A
Authority: US
Inventors: Howard C Gohs
Original assignee: ELECTRICAL FITTINGS CORP
Current assignee: ELECTRICAL FITTINGS CORP
Priority date: 1966-03-16
Filing date: 1966-03-16
Publication date: 1968-08-20
Anticipated expiration: 1985-08-20

Description

Aug. 20, 1968 H. c. GOHS THREADED LOCK WASHER AND METHOD FOR FABRICATION THEREOF 2 Sheets-Sheet 1 Filed March 16, 1966 w T N E V m 170M422! 6f fa BY W ORNEY H. C. GOHS Aug. 20, 1968 THREADED LOCK WASHER AND METHOD FOR FABRICATION THEREOF Filed March 16, 1966 2 Sheets-Sheet 2 M542 uma/ 5 4/ w a mm 06 41 5 N w a we m e w 6 -M N p 0 w m M W? s M a United States Patent 3,397,726 THREADED LOCK WASHER AND METHOD FOR FABRICATION THEREOF Howard C. Gohs, Syosset, N.Y., assignor to Electrical Fittings Corporation, East Farmingd'ale, N. a corporation of New York Filed Mar. 16, 1966, Ser. No. 534,837 4 Claims. (Cl. 15137) ABSTRACT OF THE DISCLOSURE A lock washer made of a strip of coil stock material and the process and apparatus for fabricating same. The fabricating apparatus is a multi-station forming die-punch device wherein a strip of material is cut from stock and wound on a mandrel; a locking tab is formed on the washer for preventing unwinding of the finished product. The fabricating apparatus then forms the remainder of the washer, its notches and gripping edges.

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

Threaded lock washers, 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 lock washers. First, in the stamping operation up to 80% 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 lock washer 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 equip ment and the time which is required for the operation. Third, prior art lock washers are known to often work loose after attachment to an outlet box or similar device, due primarily to the difficulty of tapping smooth 100% threads.

In my copending application Ser. No. 394,160, filed Sept. 3, 1964 and entitled Threaded Lock Washer, now US. Patent 3,260,293, there is disclosed an improved lock washer and a method for its construction. A strip of fiat 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 lock washers 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% thread is formed.) As for the final lock washer itself it is vastly superior to the prior art type of lock Washer. 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 lock washer 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 3,397,726 Patented Aug. 20, 1968 ice 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 is a general object of this invention to provide a lock washer, and a method and equipment for the fabrication thereof which are improvements over those disclosed in my above-identified application.

It has been found that electricians and other persons, when using the lock washer disclosed in my above-identified application, are sometimes apt to ruin it. A lock washer 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 look washer 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 fiat 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.

For this reason, in accordance with the principles of the present invention, a locking tab is 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 attaching 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 the upper turn is still free for relative slight rotational movement with respect to the lower turn the dual locking characteristic of the lock washer is not lost even though the upper turn is in fact a rigid unit. Thus, the locking tab insures 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.

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 lock washer with a locking tab is considerably more complex than the process for constructing the simpler lock washer disclosed in my above-identified application.

In accordance with the principles of my invention a slot is punched along the edge of the wire strip, before it is coiled, near that end which in the final coiled configuration is part of the upper turn. (At the same time, this end of the strip is rounded to further insure that an electrician will not strike it.) The strip. is then coiled on a threaded mandrel. A tab forming punch then strikes :a portion of the lower turn (an exteriorsection in the illustrative'embodiment of the invention) and forces'it to be bent up into the tab slot previously stamped near the upper end of the coil. After the locking tab engagement is made a shearing punch and die forms a series of notches and gripping tabs with biting edges on the coiled strip. The interactions between the various punches and dies is described in much greater detail below.

Before the fiat wire strip is coiled it is necessary to form a beveled V-shape along that edge which will subsequently define the threaded central bore. In my aboveidentified application the strip is shown with such a beveled edge. While such :an edge may be formed in accordance with prior art techniques I have discovered a particularly advantageous method for doing so. The simplest process for forming the beveled edge would appear to be stamping, or punching. The strip may be placed on a die whose upper surface is fiat but inclined upward directly beneath the edge of the strip to be beveled. A shear punch may then be forced downward against the strip, the lower surface of this punch being flat but inclined downward directly above that edge of the strip to be beveled. When the die and punch surfaces come against each other the beveled edge will be formed from the previously straight edge. This deceptively simple process has one major drawback. In forming the beveled edge the wire material is not cut away but merely squeezed together. The material must fiow somewhere. Unfortunately, the material is apt to flow in such a manner that the punch is pushed away from the die. The force which is generated by the flowing metal is exceedingly large. In fact, early punches used experimentally in this manner flew off the die with considerable force when contact was made; the heavy securing bolts were completely severed.

To overcome this difi'iculty I provide a groove or indentation in the shear punch mechanism. The mechanism consists of a vertically fiat blanking punch having various punch forms thereon and at its upper end the beveled-edge forming shear punch. The sheet stock is first fed up against the flat blank Wall of the punch. This wall is used as a stop to obtain the exact width of material required. As the mechanism is lowered the flat blanking punch fits flush against the vertical end of the die, on top of which rests the sheet stock from which the wire strip is to be formed. As the blanking punch falls the various punch forms cut rounded ends and the tab slot on the sheet stock. As the blanking punch continues to fall the shear punch strikes the sheet stock and exposes the recess to cut off a strip and at the same time to form a beveled edge. It is at this time that the strip would be forced out against the blanking punch to break the securing bolts. To eliminate this problem the blanking punch is provided with a groove or recess into which the metal may flow as the strip grows in width. Because the groove is included in the blanking punch it is possible to utilize a simple punching mechanism for forming the rounded edges, the locking tab slot, and the beveled edge all in a single operation.

It is a feature of this invention to provide a lock washer having gripping tabs and a screw-threaded central bore, with a plurality of helically-coiled wire strip convolutions and a locking tab for securing the upper end of the wire strip to the strip material beneath it. Itis another feature of this invention to provide a series of apparatus interacting with each other in such a manner that the wire strip is cut from sheet stock, wound and punched such that the final lock washer may be fabricated in an exceedingly simple and efficient manner.

It is a still further feature of this invention to provide a mechanism for cutting a wire strip from sheet stock, cutting it with a punch form, and forming with a shear punch a beveled edge thereon, all in a single operation.

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 fiat wire material employed to form a lock washer in accordance with the invention disclosed in my aboveidentifie'd application;

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

FIG. 3 is a perspective view of a lock washer constructed in accordance with the principles of the present invention;

FIG. 4 is a top plan view of the lock washer of FIG. 3;

FIG. 5 is a bottom plan view of the lock washer of FIG. 3;

FIG. 6 is an elevational view of the lock washer of FIG. 3;

FIG. 7 is a sectional view of the lock washer of FIG. 3 taken along the line 77 in FIG. 4; and

FIGS. 8-11 depict illustrative mechanisms for constructing the lock washer of FIG. 12.

FIG. 12 is a perspective view of the strip from which the lock washer is formed.

In my above-identified application the first step in constructing the lock washer 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 crosssection, 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 over-all 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 lock washers. 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 sufiicient force is applied. While it may rotate only slightly with respect to the lower turn it functions as a second lock washer. This dual locking characteristic is described in greater detail in my above-identified 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 absent-minded 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 lock washer of the present invention, shown in FIGS. 3-7, 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 as shown in FIG. 5 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. (Alternatively, the lower turn may contain the notch and the material in the upper turn may be bent down.) 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. 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. 4, 5 and 6 show three different views of the washer. The sectional view of FIG. 7 is included in the drawing to show the tab construction. The cross-hatched area represents that part of the washer cut by line 77 in FIG. 4. The two areas adjacent locking tab 35 represent the end view of the gripping tab to the left of the locking tab in FIG. 4. In FIGS. 6 and 7 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.

Although the construction of the 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 sufiicient 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 difiicult to build a punch which will form fi-ve 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, too, is not a simple matter particularly if all punohing operations are to be performed while the helical coil is held in place on a single mandrel.

Because of the difficulty in forming five full notches together with one half-notch, before the wire strip is wound a tab slot is formed in it. The strip 30 which is used to form the lock washer is shown in FIG. 12. This strip is cut from sheet stock. The two ends are rounded as shown and lengthwise edge 31 is beveled. Before the strip is wound in a coil, however, tab slot 51 is formed. It the strip of FIG. 12 is wound as shown in FIGS. 1 or 3, it is evident that in the teeth forming step it is only necessary to punch out five full notches 32. In this step it is not necessary to form a half-notch 51 because it is cut in the strip even before the strip is wound. The locking tab 35 may be constructed merely by bending up that portion of strip 30 immediately below slot 51 in the wound configuration. Thus, the first step in the process is to form the strip 30 shown in FIG. 12. The strip is then wound, and following the formation of the coil, the five notches 32 are punched out and the locking tab is bent up. (Preferably, the tab is formed before the notches are punched out.) The various figures on sheet 2 of the drawing show the method for obtaining stock strip 30.

Referring to FIG. -8 it is seen that sheet stock 45 is moved along the upper surface of die 48 toward blanking punch 40. The blanking punch fits snugly against the vertical end of the die. The upper rear end 49 of the die has a shape which is shown most clearly in FIG. 11. It is flat near the blanking punch and inclined upward slightly away from it. Sheet stock 45 must slide over the little hump thus formed on the upper surface of die 48. For this reason within strip guides 46 there are two stock lift pads 47. These pads not only minimize the friction of the sheet stock against the die, but in addition lift the stock sufliciently such that it slides over the hump and comes to rest against blanking punch 40.

The rear vertical end of the die is rounded on both sides and includes a notch such that punch forms 43 and 44 can be forced down against the die. As the blanking punch is forced down the punch forms cut the sheet stock to provide the two rounded ends and tab slot 51. This is shown most clearly in FIG. 9 where punch form 44 is shown cutting the sheet stock. Scrap pieces 52 and 53 are cut out and may be thrown away. Another piece such as 52 is cut away by punch form 43 if the lower end of the washer is to be rounded as is end 36.

As the blanking punch 40 continues to fall down the cutting edge of shear punch 41 bites into the sheet stock. As seen most clearly from the perspective view of FIG. 10 and the side view of FIG. 11, shear punch 41 and die 48 cause strip 30 to be cut from the sheet stock and at the same time to have its edge 31 beveled.

Recess or groove 42 is included in the blanking punch as show-n in FIGS. 8-11. In the formation of the beveled edge the strip material is squeezed. The metal must flow somewhere, and in fact it is projected in a horizontal direction toward the blanking punch. Without recess 42 the flowing metal is forced against blanking punch 40 with such force that the punch may be broken off whatever mechanism (not shown) holds it in place against die 48. Because of the positioning of recess 42, however, in the blanking punch just below the lower surface of the shear punch, the squeezed metal flows into the recess as shown in FIG. 11 without applying any force against the blanking punch. Thus, in a single step, the falling motion of the punch unit, the strip 30 of FIG. 12 is completely formed with its rounded ends, tab slot and beveled edge.

The blanking punch is preferably not raised at this time for the purpose of gaining access to the cut strip 30. Because the outer edge of the strip is fitted into recess 42 it may not be advisable to lift the blanking punch to gain access to strip 30. Instead, the punch remains stationary and a pusher rod used to push the strip out from between shear punch 41 and die 48.

Although the invention has been described with reference to a particular embodiment, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

What is claimed is:

1. A threaded lock washer comprising a plurality of turns of continuous lengthwise material forming a helix having a central opening, said turns being wound side-byside in accordance with a screw thread convolution, said turns abutting each other but being free for slight relative sliding movement, 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, a locking tab extending radially from the periphery of said lowest turn and being bent up to engage the uppermost one of said turns, wherein the biting edges of said series of tabs project axially beyond said lowest turn of said helix and each of said tabs includes a tool-striking edge, and further including a cut-out slot in the periphery of said uppermost turn into which said bent-up locking tab is fitted, said cut-out slot being larger in the circumferential direction than said locking tab and said cut-out slot having abutments which are adapted to be selectively engaged by said locking tab.

2. A threaded lock washer in accordance with claim 1 wherein said locking tab is extended radially outward from the outer periphery of said lowest turn and said tab .7 slot is included in the outer periphery of said uppermost turn.

3. A lock washer 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 but being free for slight relative sliding movement, 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 lock washer to turn around a cylindrical member when struck thereat and a biting edge which projects axially beyond the end turn of the washer, and a locking tab bent up from a lower one of said turns to engage an upper one of said turns, wherein the lengthwise edge of the material forming the bore of said central opening has a beveled V-shaped edge to provide a screw thread along said opening, and said upper turn includes a slot into which said locking tab is fitted, said slot being larger in the circumferential direction than said locking tab and said slot having abutments which are adapted to be selectively engaged by said locking tab.

4. A lock Washer in accordance with claim 3 wherein said locking tab is bent up from the outer periphery of said lower turn and said slot is included in the outer periphery of the uppermost one of said turns.

References Cited UNITED STATES PATENTS 2,902,303 9/1959 Davis 85-8.8 2,999,412 9/1961 Mantens 858.8 3,260,293 7/1966 Gohs 15137 EDWARD C. ALLEN, Primary Examiner.