US3182476A - Thread rolling means - Google Patents

Description

y 1, 1965 H. D. PRUTTON 3,182,476

THREAD ROLLING MEANS Filed Aug. 20, 1965 5 Sheets-Sheet 1 Fig. 3

INVENTOR Howard D.Prutton,

ATTORNEYS May 11, 1965 v H. D. PRUTTON THREAD ROLLING MEANS 5 Sheets-Sheet 2 'Filed Aug. 20, 1963 ATTORNEYS May 11, 1965 Filed Aug. 20, 1963 H.D.PRUTTON THREAD ROLLING MEANS 5 Sheets-Sheet 3 INVENTOR libwvzpr 1?.lrwottorc ATTORNEYS 98 96 TABLE OF DEGREES OF ADVANCE //v CYCLE May 11, 1965 Filed Aug. 20, 1963 H. D. PRUTTON THREAD ROLLING MEANS 5 Sheets-Sheet 5 FROM STARTING Poslrlalv TABLE OF SUM OF DISPLACEMENTS 0F DIES Howard D. Prutton INVENTOR ATTORNEYS United States Patent 3,182,476 TIREAD ROLLING MEANS Howard D. Prutton, Parkview, Ohio, assignor to Wire Machinery Company, Chicago, 111., a corporation of Illinois Filed Aug. 20, 1963, Ser. No. 303,372 7 Claims. (Cl. 72-88) This invention relates to a thread rolling device for forming threads on workpieces such as machine screws,

cap screws, bolts, tapping screws, studs, drive screws, screw nails, and the like.

In most present day thread rollers, headed workpieces hanging in a feed track or otherwise advanced in succession are fed to a forming station at which there is a starting finger and, depending on the type of machine, there may also be a transfer finger. The starting finger pushes the workpiece between the rolling dies in timed relation.

In most present machines, the set of dies includes a stationary die and a moving die spaced apart in such a way that as the workpiece progresses between them the thread is rolled progressively deeper until full depth is obtained.

A reciprocating-plate :type machine of inch capacity may require a stationary die 4% inches in length and a moving die inches in length. A crank drives the moving die with a harmonic motion. The harmonic motion accelerates the workpiece from zero rotative (angular velocity to a high rotative velocity at mid-stroke. At ejection the velocity is again very low. These dies usually fail at the finish end where most pressure is exerted. In recent years this type of machine has been operated at increasingly higher speeds, up to 300 pieces per minute with a 9 inch stroke. The dynamic forces generated are great and the best of balancing does not eliminate the problem of severe vibration.

In another type of thread roller, the planetary or rotary type, a higher output is achieved with lower die speeds. A ring die turns past a stationary concave die at a constant speed. Blanks or workpieces are introduced in quick sucession by a starter finger in such a manner that each workpiece starts in properly timed relationship with the dies. A disadvantage of this type of machine is that the blank tries to go instantaneously from zero rotative velocity to maximum rotative velocity. The resulting slippage between the blank and dies is difiicult to precisely control and therefore a properly timed feeding relationship between the blank and the dies cannot be perfectly maintained. The thread form correspondingly suffers. The slippage also causes the beginning portion of the die to Wear rapidly, which in turn increases the slippage in a viscous circle.

In another type of thread roller, the two roll type, one roll die runs slightly faster than the other. Again, slippage at commencement of workpiece feed is a problem. The starter finger is however eliminated.

The present invention avoids the slippage problem and also accomplishes high production speeds without the balancing and vibrational problems of reciprocating plate type machines.

An object of the invention is to provide a thread rolling device which has a reduced number of tooling parts. Those parts which must be specially designed to the manufacture of a particular workpiece may be considered tooling parts.

Another object of the invention is to provide a thread rolling device having stroking die members but having a reduced stroke to thereby accomplish a higher production speed without disturbing the balance of the stroking device.

Another important object of the invention is the provision of a thread rolling device having a high output but having dies which are lower in cost than those of prior devices having a comparable output. In a related respect, the invention accomplishes the provision of dies which are of such relatively small dimensions that carbide dies become economically feasible.

The invention contemplates the provision of a thread rolling device having a pair of arcuate thread rolling die means mounted in apposition to define between them a workpiece-passing throat. Each of the pair of die means is repetitively displaced from its own starting position through its own cycle of back and forth movement and back to its starting position to thereby establish an overall die operating cycle such that the instantaneous directions of movement of the two die means are opposed to each other throughout at least substantial portions of the operating cycle, and the algebraic sum of the respective displacements of the two die means from their starting positions remains positive throughout at least initial portions of the operating cycle, the feed direction of the workpiece being taken as positive. In one significant aspect of the invention, the algebraic sum of displacements is maintained at a positive value throughout a majority of the over-all operating cycle.

The significance of the invention and its features will be more clearly understood from the following description of one concrete example, and from the drawings in which:

FIGURE 1 is an elevational view of apparatus embodying the invention.

FIGURE 2 is an enlarged fragmentary view of the upper central portion of FIGURE 1.

FIGURE 3 is a fragmentary view taken in the plane of line 33 in FIGURE 2.

FIGURE 4 is a section taken in the plane of line 4-4 in FIGURE 1, showing the parts at extremities of their reciprocating movement opposite to the starting posit-ion.

FIGURE 5 is a section taken in the plane of line 5-5 in FIGURE 4.

FIGURE 6 is a view taken from the plane of line 6-6 in FIGURE 1, showing the dies in the starting position and also in phantom view illustrating the extremities of their reciprocating movement.

FIGURE 7 is a view similar to FIGURE 6 but with certain parts removed and with others in a centered position.

FIGURE 8 is an enlarged fragmentary section taken in the plane of line 8-8 in FIGURE 7.

FIGURE 9 is an abstract sequential representation of the thread rolling and workpiece-advancing action contemplated by the invention.

FIGURE 10 is a graph showing the arcuate displacements of the dies of FIGURES 1-8 from a zero reference point. Such displacements are plotted throughout one cycle of operation.

In order to facilitate and condense description of the invention, the following discussion of the drawings will specify reference numerals for the various parts of an illustrated embodiment and in parentheses will specify by number the figure or figures of the drawings in which such reference numerals are used to most clearly designate the parts in question. For example, cam shaft 12 (4, 5) signifies that the particular part referred to is given the reference numeral 12 and is to be conveniently found in FIGURES 4 and 5.

Description of exemplary form of apparatus Supported on one side of a base frame is a motor 10 (l) which powers a drive linkage 11 (1, 4) which in turn powers a cam shaft 12 (4, 5). An upper cam 13 and a lower cam 14 are provided for a first die to be described below. Above both these cams there are provided. an

are keyed to reciprocatingdie mountings 23 and24 respectively (4, 645). The die mounting 24 is provided with a separately adjustable die block 26. 'Upper dic clamps 2'7 and 28 are respectively provided on the mem,

bers 23 and 26. End clamping members 29 and 3d are also provided respectively on the members 23 and 26 (6, 7). A feed stop plate or flange is clamped between the clamping member 29 and the die 31 and protrudes radially beyond the face of the die.

A first die 31 is clamped by the clampingmembers 27 and 29 and a second die 32 is clamped by the clamping members 28, and 39. Wedges 33 and a wedge bolt 34 (7) are provided to adjust the position of the member 26 on the member 24 and thereby adjust the spacing between the first and second dies31 and 32. During this adjustment the draw bolts 35 carried on the memberZd are suitably loosened and tightened.

The upper ends of the die shaft 21 and 22 are received in a cover and bracing member 36 which has openings 37 formed in its top (4, 6).

The apparatus is provided with an automatic (l) of a known type for feedingheaded workpieces out .a slightly inclined discharge track 51 (l, 2). A pivoting track 52 {1-3, 6) is provided for adjusting the height at which the workpiece is fed between the dies 31 and 32, thereby determining how much of the workpiece shank will be threaded and how much will remain unthreaded. There is however at the most only a very slight angle between 52and the dies. Thisangle is somewhat exaggerated in FIGURE 2 because the angle of elevation of the track 52 is slightly exaggerated. The pivoting track 52 pivotally adjusts about the pivot axis or point 69 (2, 6), and the discharge end :of the track 52 changes height with respect to the dies 31 and 32 according to the pivotal position to which the track is adjusted.

A fixed U-frame 53 (2, 3) is mounted on the stationary frame of the machine and slidingly and guidingly receives a movable U-frame 54 in which is fixed a pin 56 which rides in the slot of a lifter arm 55 which in turn forms part of a bell crank linkage. The linkage is actuated manually. The input member is a self-locking lifter handle 66 (1, 2, 6) of a known type (such as shown forexample in US. Patents 2,703,499; 2,802,374; 2,809,720 dated respectively March 8, 1955 August 13, 1957; October 15, 1957) which is so arranged as'to allow the arm 55 and therefore the pin 56 and U-frarne '54 tobe positionally adjusted by manual movement of the handle 66' along the fixedlocking quadrant 67- but, in any adjusted position, lock the lifter arm 55 against loads imposed from the U-frame 54 through the pin 56.

Threaded adjustment knobs 57 (2, 3, 6) are engaged on either side of the movable U-frame 54 and bear against the sides of the pivoting track 52. Lock bolts 58(3) extend through the centers of the adjustment knobs 57 into engagement with the sides of the pivoting tracks 52. Similar rear adjustment knobs 59(2, 6) are provided having lock bolts 60 received in their centers and engaging the upper end of the pivoting track 52. The knobs 57 and 59 provide for adjustment of the spacing between the two sides of the track 52. The knobs 59 and lock bolts 60 are centeredfon the pivot point or pivot axis69.

A workpiece holddown bar 62 (l-3, 6) isfastened by releasable-rear and front clamping screws 63 (2, 3, 6) which hold the bar 62 against spacers 65 integrally attached to the movable U-frame 54. The screws 63 are received in slots 64 (2, 3) formed in the spacers 65. Note that the spacing of the bar 62 above thetrackSZ may. be

hopper i adjusted by changing the vertical positions of the screws 63 in the slots 64.

A workpiece-receiving discharge bin 63 (l) is provided on the outfe'ed side of the apparatusbelow the dies.

It may be noted that the camel?) and 14 are of slightly The cams 13-16 are so shaped so that the dies 31 and 32 have the oscillating movement plotted in FIG- URE 10. The starting or zero displacement position of each of the diesis that position shown in FIGURE 6.

The position of each die shown in FIGURE. 6 is the position at which each successive workpiece starts its rolling contact with the dies. 7

In this starting position of the dies, the feed stop member 25 on the die- 31 is spaced slightly beyond the terminal end of the'feed track 52. The shank of each successive. workpiece coming out of the tracks terminal end comes to rest against the feed stop which holds the workpiece square with the .dies. Although only a few of the workpieces are shown inthedrawings, it willbe understood that they progress inv adjacent succession along the tracks 51 and 52.to the terminal end of the track 52. The terminal'end of the track, 52 is not visible in FIGURE. 6 because it underlies the holddown bar 62. In order for the track 52 to extend sufiiciently deeply within the throat 70 (7) formed between the dies 31 and 32, it may be relieved at its sides toward its free end'as at 61 (6). Although the lower or free end of the holddown bar 62 appears to interfere with the dies 51 and 32 in FIGURE 6, it will be understood 'that such holddown bar ordinarily extends over the top of the dies as does the workpiece head.

First and second dies are schematically illustrated in FIGURE 9, and correspond to the dies, 31 and 32. FIG- URE 9A shows the first and second dies at a starting position corresponding to the starting. position illustrated in FIGURE 6. FTGURE 9B shows the dies A cycle or degrees later than the starting position. FIGURE 9Cshowsthe dies /2 cycle or degrees later'than the starting position. FIGURE 913 shows the dies cycle or 270 degrees later than the starting position. FEGURE 9B shows the dies one full cycle or-360 degrees later than the original starting position. The position illustrated in FIGURE 9B is of course the beginning of a new cycle and the positions illustrated are therefore identical to those shown in FIGURE 9A.

In the diagrams of'FIGURE 9, 'a reference line 8 is drawn at the narrowest part of the throat. between the first and second dies.- Using an arbitrary unit of length, a displacement scale is then indicated as being marked off on'each of the dies. For both dies, at the starting position the zero point of the scale coincides with the line 86, thus'indicating, that the displacement of each die from the starting position is zero in the starting position.

Since movement of the dies downwardly past the line 80 is movement in the feed direction, which'may arbitrarily be chosen'as the positive direction, and conversely movement upwardly through the line 88 is movement in the antifeed direction which may be chosen as the nega tive direction, the scales maybe laid of1 in the manner illustrated so that the intersection of each scale with the line 80 actually indicates on the applicable scale the positive or negative value of die displacement.

The ,sequenceof changeof die positions shown in FIGURE 9 is intended merely to schematically illustrate the invention. "The unit length marked along the arcuate die faces, the, motion, and the starting position of the workpiece have been chosen in such a way as to=rnost clearly interrelate the die movements with the translation of the workpiece by simple numerical relationships. If a workpiece W is engaged by the first and second dies at the starting position as in FIGURE 9A and the dies move to the position shown in FIGURE 9B, the workpiece will advance linearly by A the unit length marked along the illustrated arcs because the albebraic sum of the arc displacement is /2 at the position shown in 93. During this translation of the workpiece W, it will rotate in the direction shown by the arrow 81, and threads will commence to be rolled on the shank of the workpiece. It is only the shank of the workpiece that is illustrated in the schematic illustrations of FIG- URE 9. Thread rolling continues as the dies move from the position shown in FIGURE 93 to the position shown in FIGURE 9C. Throughout the movement from the starting position shown in FIGURE 9A to the position shown in FIGURE 90, the dies move in the directions indicated by the arrows 83 and 84. Thread formation continues and the workpiece W continues to rotate in the direction 81 as the dies move from the position of FIG- URE 9B to the position of FIGURE 9C. However it is to be noted that the workpiece does not advance between these two positions of the dies. This is because the algebraic sum of the displacements of the two arcs from their starting position remains /2. Thus the arcuate scales in FIGURE 9B show a displacement of +1 /z for the first die and l for the second die, giving an algebraic sum of /2. In FIGURE 90 the arcuate scales show a displacement of +4 for the first die and 3 /2 for the second die, so that the algebraic sum of arcuate displacements remains /2. Therefore, as noted, the workpiece does not advance between FIG- URES 9B and 90, but is rolled between the dies with a pure rolling motion.

At the position shown in FIGURE 9C, the first and second dies are changing their directions and are momentarily stationary. The workpiece therefore is not rolling. However this is only an instantaneous condition and shortly thereafter the workpiece commences to roll in the direction shown by the arrow 82. The first die now commences to move in the direction shown by the arrow 85, but more slowly than the movement of the second die in the direction shown by the arrow 86. Thus when the position of FIGURE 9D is reached, the positive displacement of the first die has only been decreased to +3% from the +4 value of FIGURE 9C, a net change of /2. However the negative displacement of the second die has changed from 3 /z in FIGURE 9C to -2 in FIGURE 9D, a net change of +1 6" Thus there is an over-all change of +1 from the algebraic sum obtaining at the position of FIGURE 9C. The workpiece advances by half of this over-all change of +1 and therefore the workpiece advances a linear distance equal to /2 the unit arcuate length which was marked olI on the first and second dies in the diagram to the position shown in FIGURE 9D. The position of FIGURE 9D therefore represents an advance of 6. unit length from the narrowest point of the throat between the dies, that is, from the zero reference line 80. At this position, the algebraic sum of arc displacements is at a maximum value of +1 /2.

Actually the workpiece W does not quite reach the position shown in FIGURE 9D since this represents the extreme workpiece advance capability of the dies, and the parts are dimensioned so that the workpiece W disengages from the now widening throat between the thread forming dies very shortly before the workpiece reaches the position shown in FIGURE 9D. It is to be noted that the diagrammatic illustration relates to a system where the distance the system is capable of advancing the workpiece beyond the throat is twice the distance that the workpiece W advances as it moves from the starting point of FIGURE 9A to the narrowest part of the throat. This exact relationship of two-to-one is chosen in order to illustrate the invention with simple length relationshps. However, it is desirable in any event to have the outfeed length capability of the system exceed the infeed length so that the workpiece may be released even after accounting for the increase in diameter of the workpiece shank due to thread rolling and consequent growth of the outside diameter.

Therefore it should be clearly understood that the workpiece W shown in FIGURE 9D is shown at its hypothetical position which it would have if it had not already passed out of engagement with the first and second dies. In the diagrammatic showing of FIGURE 9, a showing of the initially increasing and then decreasing degrees of interference between the die face and the workpiece W has not been attempted. The increasing and subsequent decreasing of such interference is due of course to the narrowing and subsequent widening of the throat between the dies as the workpiece passes through this throat. When the interference becomes zero, the workpiece can drop free.

So far the description has assumed that release is by gravity. This ignores the fact that there would be interference between the dies and the head of the workpiece, causing the workpiece to hang up on the dies. However a simple gravity release may be suitable in some cases, particularly when the workpiece does not have a head. In other cases, the inertia of the advancing movement of the workpiece is relied upon.

From the position of 9D and with the workpiece now released, the dies move rapidly back to the starting position shown in 9E. It is to be noted that during this movement the algebraic sum of die displacements changes from +1 /2 to Zero, a net change of 1 /2. This negative change may commence immediately after release of the workpiece W. If the head diameters of the workpieces are greater than the length of die-contacting travel of the workpieces, as is true of many standard bolts, a succeeding workpiece will reach the starting position shown in FIGURE 9A only upon release of the workpiece W shown in FIGURE 9D.

Since the algebraic sum of arc displacement changes negatively in going from FIGURE 9D to FIGURE 9E, such succeeding workpiece will automatically be urged in a backward or antifeed direction (i.e., into the discharge mouth of the track 52), and will continue to be so urged until the parts reach the position shown in FIGURE 9E at which time the feed stop (flange 25 in the actual apparatus of FIGURES 1-8) will square the workpiece with the dies and the next cycle will commence whereby the workpiece will be drawn into the throat between the dies as previously described. Thus no separate feed mechanism whatsoever is required to transfer the workpieces from the end of the feed track 52 to a die-engaged condition. No escapement means is required to restrain succeeding workpieces until their turn foir processing arrives, for standard workpieces, since the advance of the workpiece does not exceed the normal head diameter. An escapement (not shown) may be employed when the workpiece are headless or have heads of small diameter.

The above description of the schematic illustration of FIGURE 9 utilizes simplified numerical relationships between the length values of the workpiece-feed-path and the arcuate distances along the first and second dies, and in order to do this it assumes that the dies release the workpiece prior to the 270 degree point in the cycle. However the cam drive arrangement can be such that the dies actually continue to roll the workpiece for something more than 270 degrees of the cycle, thus minimizing the portion of the cycle not devoted to actual rolling of threads, and increasing production capacity. Furthermore, the workpiece can receive a little kick near the end of its forward travel so as to more positively discharge workpieces, including those with relatively large heads.

' duced by-the combination: ofgtherelatively 93in the curve i. The sleep slopenp'o'rti URE' 10 and is the motion which the machine' illustrated,

in FIGURES 1-8 is designed toaccomplish'. Die dis? placement values are in inches. 1 Die 31 moves back'and forth through a greater distance than die 32 in the.illus.- trated machine. The displacement of. the die ;31 is'shown by thecurve 91 andthe displacementof the die 32 by the curve 92. The algebraic sum of the die displacements is plotted by the curve 93. The values ofthe CI11'V6193. divided by two produce the curve 94 which is a plot of workpiece displacement, with zero workpiece displacement corresponding to, the point at which therworkpiecei firstengages the dies; 1 V n The negative slope portion 95 f the curve 94 istheo retical since the workpiece has-atthis stage passed out of. contact with the dies and been ejected; However this negative slope clearly establishes that there cannot bean advance of a succeeding workpiece which may be presented to the dies at the outfeed mouth of the track 52 at say about the ZIO -de reestage, of the cycle; a

. 2 balancing problems and making possible a 'more compact operating cycle. and the use of less costly diesQL l The invention is, not restricted to the slavishjmitation ofieach and every onezof'the details described above whichhave been. set forth merely byway of example with the intent of most clearly setting forth the teaching of the invention. Obviously devices may be provided which change, eliminate or add certain specific structural detailsiwithout departing from the invention. What'is claimed is: p 1. a e I 1.1A thread rolling device comprising-.firstand-second a'rcuate thread-rolling die means mounted in apposition to define betweenthema WQrk iece passin'g throat for passing .w'orkpiecesina'fgiven directionfand r'olling The abrupt upward slope 96 inthe curve 93 prov teep}; slope ateda at 971 in the' curve 92- together' ith t-hefdwe curve 94" corresponds ;to the steep slope portion 9510i steep. Since a s'teep'slope corresponds to a highvclocitigl the workpiece, willthereby have a high momentum in' fth'efeed direction as-it is releasedfr'om the dies, and'thereb even large-headed workpieces will clear the dies .with ea when they are released.

. It should be noted that thehorizontal portion o f ithe central part of the curve 94 signifies that the workpiece is being rolled and. threads are being formed thereon,

even though the workpiece is. dwelling in its feed advance. 40 It should further be noted in the illustratedexample'. that the algebraic sum of die displacements represented;

T hisproduces a thread. of superior roundness.

by the curve 93 is *at a positive value or at zerothrougli out the operating cycle. Clearly, therefore, the algebraic sum remains at 'a positive value' th'roughout at 'least a majority of the operating cycle; The negative slope vatthe. right hand end of the curve 533 where it becomes con gruent With the curve 9am the particularillustration of;

FIGURE corresponds" to negative values of-..the; suint ot instantaneous velocities of the dies 31" and 312.; Such negative values apply from just beyond the 270Qdegree' point to the'360'degree point where the'over-all operating S r cycle is completed.

It is particularly to be noted that in initial stages the curve 4 has a low gentleslopejcorrespouding'tollow feed or'advance' velocities or to zerovelocity at; thefiat portion. The rate of change of the slope ofthe gcurve 94 is also reasonably low at initialportionsot.thecurvealthough not as low as at the center portion'oi the; curve (where velocity and acceleration are bothzero assuming thatthe curve is absolutelyhorizontal), ,The relatively low acceleration at the beginningof the. curve is advana i'ngi said afoiementroned said overkall.operating-cycle. 1

1 5 ."A 'deviceas definedin'clairn 1 whichsaid 'meansl forirepetitivelydisplacing saidffirst'and seceriddie means and forming them during their'passage, means fo'rrepetilish an over-all; die operating cycle, with the instantaneous directions ofmovement'of saidfirst and second die means ble'ingloppos edtoeachi ther throughout at: least 'substan lldi'eloperating cycle'and tak 7 given .direction 1 as. positive, the algebraic zsumfioff the vrespective}displacements of the first and.-se-eond diexineians from 'theirfstarting' positions remaining positive throughout-at leastt ini-tialportions of repetitively displacing, said first and Second die means es ansrtorz rnai'ntainin said algebraicisumat a.

alue" {throughout a majority of said over-all op cycl. a

evice as defincd: iniplairn in Whichsaid means ely displacing said'firstand second die means eanis'igforl'maintainingsaid algebraic sum ata lue ori-zero" throughout "all of "said over-all ing;cycle:.1 Ardevice 'as'defined in claimgl in whichtthe value of saidalgebraicrsum: changes-in the negativedirection the value ofgthez' sum ofJthe instantaneous yeth'e :fiISili'B-Dd second die means, remains negas I said overtallioperatirrg cycle is. being centincludes 'means for", maintaining a substantially constan value ofisaidalgebraic sumduring an interval which com mences at a latertime': than the beginning of said over all operating cycle and which concludes prior. tothe attainment ofthe maximum positive valuev of-said algebraic sumduring saidover-all operating cycle.-

tageous in making for a smooth rolling and thread formtion, but only through the I provision of relatively. long dies and a relatively "long-path of die movementboth.

of. which are avoided in the'prcs' ent-invention, eliminating v '6. A device as defined in claim 1 including means for I supplying a succession of. oriented workpieces 'with said i succession oii oriented workpieces beingurged in theteed direction-through. a discharge endof said supplying means at the inputside .of said workpiece passing throat.

.-. 7.,A; device as defined in -claim='6 inxwhich the value" of said algebraic sum changes, in the. negative direction 'while zsaid overvall operatingcycle is being'completed.

V ReferencesCited the Examiner UNITED STATES PATENT Z TO EIG P TENT, 215,044 :1 /:O7. LGermany.. MICHAEL v; BRIND'I'SI, Primary Examiner.

Claims (1)

1. A THREAD ROLLING DEVICE COMPRISING FIRST AND SECOND ARCUATE THREAD-ROLLING DIE MEANS MOUNTED IN APPOSITION TO DEFINE BETWEEN THEM A WORKPIECE-PASSING THROAT FOR PASSING WORKPIECES IN A GIVEN DIRECTION AND ROLLING AND FORMING THEM DURING THEIR PASSAGE, MEANS FOR REPETITIVELY DISPLACING SAID FIRST AND SECOND DIE MEANS EACH FROM ITS OWN STARTING POSITION THROUGH ITS OWN CYCLE OF ARCUATE BACK AND FORTH MOVEMENT ALONG A SIDE OF SAID THROAT AND BACK TO ITS STARTING POSITION TO THEREBY ESTABLISH AN OVER-ALL DIE OPERATING CYCLE, WITH THE INSTANTANEOUS DIRECTIONS OF MOVEMENT OF SAID FIRST AND SECOND DIE MEANS BEING OPPOSED TO EACH OTHER THROUGHOUT AT LEAST SUBSTANTIAL PORTIONS OF SAID OVER-ALL DIE OPERATING CYCLE AND, TAKING SAID AFOREMENTIONED GIVEN DIRECTIONS AS POSITIVE, THE ALGEBRAIC SUM OF THE RESPECTIVE DISPLACEMENTS OF THE FIRST AND SECOND DIE MEANS FROM THEIR STARTING POSITIONS REMAINING POSITIVE THROUGHOUT AT LEAST INITIAL PORTIONS OF SAID OVER-ALL OPERATING CYCLE.

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