US2937548A

US2937548A - Strap wrench device

Info

Publication number: US2937548A
Application number: US727361A
Authority: US
Inventors: Robert H Mckim
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-04-09
Filing date: 1958-04-09
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24

Description

May 24, 1960 R. H. McKlM STRAP WRENCH DEVICE 2 Sheets-Sheet 1 Filed April 9, 1958 INVENTOR. Robert H A/cK/m ATTO R/YEY United States Patent This invention relates to a device for opening screw fitting lids from jars and bottles. It is of the strap wrench type and is used for holding a circular object in a fixed position while screwing or unscrewing a second object into threaded engagement therewith or into disengagement therefrom. Jar lids and bottle lids constitute a group of circular objects for which the device is especially suited.

Devices for this purpose as heretofore constructed have generally been complicated, often requiring that the ;operator have particular knowledge of what constitutes the most effective position of the circular object with-relation to the device for optimum utilization of the tightening principle inherent in the device. In fact it has been possible for the operator of the device to tighten the strap against the circular object and operate the device upon having unwittingly placed the circular object in such position with relation to the device that it would be impossible for the tightening principle to come-into play.

Another disadvantage has been that the operator must use one of his hands to pull upon the strap during the entire operation of turning the object into or out of threaded engagement with the jar lid or other circular object involved. In an attempt to avoid this, resort has been had to different kinds of clamping, hooking, or

locking devices to hold the strap tightly around the circular object with the result oftentimes of damage to the strap.

Irrespective of the damage to the strap from such sources, the general wear and tear encountered with previous devices has been great. Metal chain straps sometimes found in strap wrench types of devices are not only expensive but they severely dent or otherwise dam age the lids of most jars. Moreover, because chains of adequate strength must possess large links, they do not readily fit around small diameter objects such as the lids of small bottles. To accommodate the lids of both very small and very large jars and the like, the strap must have considerable flexibility and a breaking strength of the order of one thousand pounds or greater (for a conventionally desirable safety factor, of, say, 5), and this strength must reside in a strap of about one quarter to three eighths inch in width for use with lids of both small and large jars. Cloth, rope, and leather straps are not strong enough when of the narrow width required by a jar opening device. Thin steel straps are not satisfactory. For one thing, when wrapped about the lid of a small bottle, kinks or other deformities are likely to develop, making frequent renewals of the strap necessary.

Still another problem attending the devices heretofore employed has been the storage of the unused portion when changing from objects of large diameter, such as lids of large jars, to those of small diameter. In going from the former to the latter a long unused portion of strap must dangle in a loose and unsightly manner from the device if it is not stored away in some manner. In attempts to do this by winding the unused portion upon 2,937,548 Patented May 24, 19 60 a spool, the unwinding of the stored portion usuallyresults in the coils spreading out from the spool and coming in contact with and wedging against the containing walls or other stationary parts of the device, thereby locking the spool against any reverse turning intended for unwinding the coil, and making it necessary for the operator to use his hand on the strap to pull it oh the spool.

It is an object of this invention to provide a device of the strap wrench type for use in holding a circular object, such as the screw lid of a jar or bottle, while a second threaded object is turned into threaded. engagement therewith or disengagement therefrom, by which,

when the strap is looped around and tightened about the circular object the said object is automatically positioned in relation to the device for the optimum utilization of the tightening principle inherent in strap wrench type of devices, and which does'not, therefore, require that the housewife or other operator of the device have knowledge of where to place the circular object for the most effective operation of the device. v 'It is a further object of the invention to provide means whereby when the strap is tightened about the jar lid, the lid is pulled into a relationship with the device'whi'ch gives the maximum gripping friction between the strap and the lid possible within the limitations of the workable tensile strength of the strap and the wide'rang'e' of diameters of jar lids or other circular objects that are intended to be handled by the device, or in other words which prevents overstressing the strap while still providing adequate gripping friction of the circular object.

Another object is to provide a device of the strap wrench type which does not require that the free end of the strap be held and pulled by the operator during the gripping action of the strap, the strap being hand tightened only to the extent for positioning the jar lid, the actual tightening for gripping being self-acting and coincident with the application of torque to the jar. Both hands of the operator are thus free to apply a turning force to the jar.

Still another object is to provide a device in which, coincident with the foregoing self-tightening gripping action of the strap, there is a self-locking action created by friction of the strap against an element of the device to keep the strap held tightly around the jar lid during turning of the jar, thereby eliminating the necessity for damage the strap. A further object is to provide a device of the aforesaid type which may be used for both large and small diameter jar lids or other round objects and wherein storage of the unused portion of strap when the device is used with small diameter objects is obtained by winding it upon a spool or similar device and whereby the tendency of the coils of strap during unwinding to become locked against the inner walls or other parts of the device is precluded.

A further object is to provide a strap for a device of the aforesaid type which is narrow enough for use on all commercial jar lids, flexible enough for bending around lids of very small diameter without taking a permanent deformity, strong enough for use with large diameter lids, and has a coeflicient of friction large enough to grip lids of all diameters.

These and other objects and advantages of the invention will appear from the ensuing description and appended claims.

The invention is illustrated by way of example in the accompanying drawings and is described in detail hereinafter. The particular constructions herein shown and described are to be construed as illustrative only, and not as limiting the invention.

means In the drawings:

Fig. 1 is a view in perspective of the device operatively applied to a screw-fitted jar lid.

Fig. 2 shows a horizontal section of the body of the device on line 2-2 of Fig. 1, said section being above that portion of the strap which is within the body of the device.

Fig. 3 is a sectional view on line 3-3 of Fig. 2 plus a small portion of the strap shown diagrammatically.

Fig. 4 is a plan view, partly in section, of a form of the device similar to the device of Figs. 1-3, except for a different spindle arrangement on which the strap may be wound.

Fig. 5 is a sectional view on line 5-5 of Fig. 4, plus a small portion of the strap shown diagrammatically.

Fig. 6 is an end elevation view of a modified form of the device operatively applied to a screw-fitted jar lid.

Fig. 7 is a horizontal sectional view on line 77 of Fig. 6 taken above the strap.

Fig. 8 is a front elevation view of the device of Fig. 6 but without the jar lid and the portion of strap around said jar lid.

Fig. 9 is a view in horizontal section showing a modified form of the device shown in Fig. 7.

Fig. 10 is a side elevation view of a strap used with my device.

Fig. 11 is a view of the strap from line 11--11 of Fig. 10.

Fig. 12 is a section on line 12-12 of Fig. 10.

Fig. 13 illustrates a common strap wrench with a certain feature of my invention diagrammatically illustrated and superimposed thereon.

Referring to the drawings, a flat, box-like housing, designated generally by the reference numeral 10, is comprised of a top plate 11 and a bottom plate 12 (Figs. 3 and 5). Said plates may, if desired, be generally rectangular in shape. They are spaced apart and fixed parallel to each other by any suitable means, such, for example, as by forming either of said plates into a right angle flange at its two ends, said flanges serving as supports for the other of said plates by soldering or otherwise securing said other plate to said end flanges. In the structure as shown in Fig. 1 the top plate 11 is thus flanged to form end pieces 13. The sides and ends of said housing, however, may or may not, as desired, be left open between the said two plates, except for a distance along one side as hereafter explained. The said housing may, if desired, be die cast into one monolithic flat box-like piece having the said upper and lower plates. A preferred manner of use of the housing embraces having it secured to a wall or other suitable vertical surface with the said two plates in a horizontal position. Any suitable means may be employed for so securing said housing, such as by forming the bottom plate into a downwardly extending flange 14 along the rear side of the housing, said flange being provided with appropriate holes fitted with screws 15 for engaging such wall 15'.

Desirably, although not necessarily, there is provided a narrow plate 16 along a portion of the front side of housing 10 between the top and bottom plates 11 and 12, and rigidly secured, by any suitable means, with respect to said plates. The outer face of plate 16 may be flush with the front edges of plates 11 and 12 or, for reasons hereinafter explained, it may be recessed so that its outer face lies behind the plane of the front edges of said plates by any desired distance less than the thickness of the strap used with the device. In the construction as shown in the drawings the outer face of said plate 16 is flush with said edges of said plates and is obtained by forming the lower plate 12 into an upwardly extending flange which has its upper edge adjacent to upper plate 11. The length of said plate 16 is such as to leave an open space between the top and bottom plates at the right hand end of the front side of the housing 10 sufficient for the working of the strap therethrough for engagement of said strap with jar lids, and other round objects, of different diameters as hereinafter explained. This said open space is designated by the reference numeral 17, a portion of said opening being seen back of the jar lid in Fig. 1. The said narrow plate 16 may be of only short length since, as will be seen later, it need extend only a short distance to the left of the said opening 17. That portion of the forward edges of plates 11 and 12 which bound the said opening 17 constitutes what I term the working edges 17 of my device. These edges should lie in a plane perpendicular to the top and bottom plates. Preferably this plane should be a flat plane.

A fulcrum member 18 (Fig. 2), rigidly secured to the housing 10 between the top and bottom plates thereof, has an arcuate-shaped surface, which said surface begins at the right hand terminus of the narrow plate member 16 and extends inwardly therefrom first to the right and thence to the left so as to present a smooth and inwardly extending recurved surface on which, as later seen, the strap of my device is positioned after the said strap has been placed about the circumference of the jar lid. In the construction as shown in Figs. 1 to 3 the said arcuateshaped member 18 is formed as a continuation of the flange which constitutes the narrow plate member 16, as if a portion of the flange had been sawed free from the floor plate to form a free end and the said free end bent inwardly into the said arcuate or recurved shape. The said arcuate surface is preferably corrugated or otherwise roughened to increase its friction to the strap.

A spindle, designated generally as B (Fig. 1), is rotatably positioned on floor plate 12 and extends axially upwardly through the top plate 11, said top plate being appropriately provided With a circular opening through which the said spindle rotatively fits. Desirably, though not necessarily, the spindle 19 is made up of two separate sections, a lower spindle section 20 extending from the lower plate 12 to upper plate 11, and an upper spindle section 21 extending upwardly through the aforesaid circular opening in upper plate 11, the said two sections being rigidly secured together and the upper spindle section 21 serving as a means by which the said spindle 19 is manually rotated. A disc 22, coaxial with spindle 19, is positioned between, and rigidly secured to, the two

spindle sections

20 and 21 and is provided with a circumferentially positioned and downwardly extending flange 23, the width of said flange being some fractional part, preferably not all, of the vertical distance between the upper and lower plates 11 and 12 of the housing 10. The said disc is of suflicient diameter that an annular space exists between the lower section 20 of spindle 19 and the said flange 23 of radial width great enough that the unused portion of the strap 24 can be wound flatwise upon the spindle to occupy the said annular space between the spindle and the said flange. The vertical distance between the upper and lower plates 11 and 12 of the housing 10 is such that when the unused portion of the strap is wound as aforesaid upon the said spindle the upper and lower edges of the coiled sections of the strap are in close proximity to the lower plate 12 and the disc 22, as seen in Fig. 3. The strap 24 is wound flatwise upon the spindle and analogously to the winding of a ribbon upon a spool, but it will be noted that it must be passed underneath the lower edge of the flange 23 before it can be wound upon the spindle. In order to permit the strap to be passed edgewise under the said flange the lower plate 12 is appropriately cut away, as shown at 25 in Figs. 2 and 3, in an area extending from near the arcuate-shaped member 18 to a point beyond the position where the strap must pass under the flange 23. Other means may be employed to permit the strap to pass under the flange 23. For example, the floor plate may be appropriately depressed or grooved downwardly to permit such passage. In the unwinding of the strap from the spindle the strap again passes edgewise under the'lower edge, of the flange 23, but in the reverse direction.

It will thus be seen that the circumferential flange 23 serves as an outer confining or retaining wall for the coiled portion of the strap 24. It will also be seen that as the spindle is turned to unwind the coiled strap, this retaining wall rotates with the spindle and that in any spreading out of the coils from the spindle the strap comes in contact with this rotating wall so that there is prevented any contacting of the spreading coils against stationary parts of the housing which might lock the coils against said stationary parts. Thus the operator is not required to use his hand on the strap itself to pull and unwind it from the spindle.

In Figs. 4 and 5 there is shown an alternate construction for the rotatable retaining wall which serves as above explained to prevent the locking of the unwinding coils of strap as the spindle 19 is rotated to unwind the strap. A disc 26, coaxial with spindle 19, is rigidly secured to the lower end of spindle 19 and is provided with a circumferentially positioned and upwardly extending flange 27 which corresponds to the downwardly extending flange 23 of the construction shown in Fig. 3. The upper plate 11 is provided with a downwardly extending protrusion 28 which serves to hold the coils of thejstrap in position adjacent the disc 26 and contained within the flange 27. With this construction the top and bottom plates are spaced apart suificiently to allow the strap to pass edgewise over the flange 27 and under the member 28, thus avoiding grooving or cutting away a portion of the upper plate to permit passage of the strap over the flange 27.

The end of the aforesaid strap 24 which is not in use during the operation of the device is secured, by any suitable means, to the lower spindle section 20 whereby the unused portion of the strap will be coiled upon the spindle when the latter is rotated. The other end of the strap is anchored at the point A (Fig. 2) by any suitable means such as bracket 29 secured to the floor plate 12 and the end of the strap appropriately attached to said bracket, the location of the said point A being hereinafter more fully defined. From the fixed anchorage point A the strap extends outwardly through the opening 17 of the housing 10, thence about a circumferential part of a jar lid 30 (which is screw fitted to jar 31) when said jar lid is in a position tangent to the said working edges 17' of said housing at the said opening 17, ,thenceback through said opening 17 and over the aforesaid arcuateshaped fulcrum member 18, from whence the remaining portion of the strap extends to and is coiled upon the aforesaid spindle section 20.

A modified form of the device of my invention is shown in Figs. 6 to 8 in which there is omitted the means for storing within the device the surplus or unused portion of the strap when the device is used with threaded bottle or jar lids or other small round objects of small diameter. The housing, designated generally as 100, is of the same general, flat, box-like structure as the housing 10 of Figs. 1 to 3 incl., and may, if desired, be adapted for mounting upon a wall or other appropriate vertical surface 101 by suitable means, such as bracket 102 and screws 103. The front side of the housing 100 is analogous in every way to the front side of housing 10 of Figs. 1 to 3 and is provided with a front opening 104, working edges 104, a narrow plate member 105 and the arcuate-shaped member 106, all of which correspond respectively to the opening 17, working edges 17, the narrow plate 16 and the arcuate-shaped member 18 of the form of device shown in Figs. 1 to 3. One end of the strap 24 is anchored at point A by any suitable means such as bracket 107 secured to the floor of the housing 100. An opening 108 is provided in the left hand end wall of the housing through which the unused portion of the strap 24 passes after around jar lid 109, thence back through the opening 104, and over the arcuate-shaped member 10 The location of point A (the anchorage point of the strap) will be explained by reference to Fig. 7 wherein the strap is tightly pulled about the jar lid 10? so that the jar lid is positioned tangentially against the working edges 104 and tangentially against that portion'of the strap that passes over the arcuate-shaped member 106 at point D. In Fig. 7, point A, as hereinbefore stated, is the anchorage point for the fixed end of the strap, point B is the first point of tangency which the strap makes with the jar lid, point C is the center of the jar lid and point D is the second point of tangency of the strap of the jar lid where the strap leaves the lid and begins contact with the arcuate-shaped member 106. The angle included between lines AB and CD is termed angle a. The anchorage point A should be so located that the lines AB and CD intersect at a point which lies on the side of the working edges 104 toward the housing 100, and not on the opposite side of said working edges. Thus the point A should not be located too far toward the right-hand side of the housing shown in Fig. 7, since with small bottle caps and jarlids or other small-diameter objects, that would throw the apex of the angle a front of the working edges 104', i.e., on the opposite side from that shown in Fig. 7.

Fig. 9 shows a modified form of the device shown in Fig. 7, the sole modification beingthe positioning of the working edges 104 by a distance y in front of and parallel to the narrow plate member the distance y being a fraction of the thickness of the strap, said fraction depending upon the resiliency of the strap material, and being generally about half the strap thickness. This modification afiords an increase in the size of the angle a, which is desirable where the device is to be used for small jar lids and other small-diameter objects where more friction is required for proper grip on said object.

With respect to the strap to be used, I prefer to employ the strap construction shown in Figs. 10, 11, and 12. A

pair of flexible aircraft-type steel cables 150, having a breaking strength of around 500 pounds each, positioned parallel and spaced slightly apart, are imbcdded in a flexible rubber or plastic jacket 151, approximately rectangular in cross-sectional shape, with the major axis of said rectangle cutting across the axes of said cables. Instead of the said two cables, one cable of strength equivalent to the two cables may be positioned on the central longitudinal axis of said flexible jacket 151. Preferably each of the two sides ofthe strap is provided with 'a succession ofribs 152 so as to give a corrugated surface throughout substantially the entire length of'the cable,

surface in the operation of the device. It is also preferable that these corrugations approximate the conventional corrugations found in jar lids. In order to fit the narrowest of commercial jar lids, the strap should be approximately inch in width; and to be sufliciently flexible for bending around lids of small diameter, its thickness should be approximately /8 inch. The material comprising the jacket surrounding the cables should have a coeflicient of friction (strap-to-metal) of at least 0.5, and the general physical characteristics, particularly as to flexibility and strength, as those possessed by a flexible grade of polyvinyl chloride plastic material.

To operate the device, as for example in loosening a. tightly screw-fitted lid from a jar, the jar is held in one hand while the lid is placed within the loop of strap in front of the working edges of the housing. Ifthe device is of the form shown in Figs. 6 to 8 wherein the unused portion of thestrap is not coiled within the housing, the free end of the strap is then pulled with the other hand until the strap pulls the jar lid into firm tangential contact against the working edges of the housing and the strap makes firm contact with the circumference of the lid.

mamas As soon as positioning of the jar lid and strap is effected the jar can be gripped with both hands and a clockwise turning force exerted to unscrew the lid from the jar. .If the device is of the form shown in Figs. 1 to 5 wherein the unused portion of the strap is wound upon a spindle for storage purposes, the operation is essentially the same except that the hand not holding the jar is used to rotate the spindle to wind enough of the strap thereon to position the jar lid tangentiflly to the working edges of the housing and to bring the strap into firm contact about the jar lid. As soon as the jar lid and strap are thus positioned and torque is applied to the jar, no further pulling force need be applied to the free end of the strap--the strap grips the jar lid with ever increasing tightness as torque is increasingly applied to the jar.

An important feature of my device is the incorporation of the working edges 17 in Figs. 1 to 5 and 104 in Figs. 6 to 8 against which jar lids of various diameters may be automatically positioned with relation to anchorage point A and the arcuate-shaped member (18, Fig. 2; 106, Fig. 7) so that, as hereinbefore explained, angle (1" is such that the strap adequately grips the jar lid without being overstressed by the torque that is applied to the jar.

The importance of this working edge feature of my device may be further emphasized by reference to Fig. 13 which illustrates a common strap wrench with a circular object to be held therewith shown in two positions-one wherein the self-tightening principle comes into play and the other wherein this principle cannot come into play. The strap 113 is fixed at one of its ends to the wrench handle 114 at the point 115 and after being applied to the circular object 116, passes over the knob or fulcrum member 117 at the end of the wrench. In this solid circle position 116 the two lines which define angle "a, converge on the same side of the device as is the anchorage point of the strap and, therefore, the self-tightening principle is operative, and after original positioning is accomplished, no further pulling force need be applied to strap end 118 in order for the strap to grip the jar. In the dotted circle position 116', however, the apex of said angle a lies on the opposite side of the device from the anchorage point of the strap and the said self-tightening principle is inoperative, requiring that considerable pulling force be applied to strap end 118 in order that the strap grip the jar. The rectangle shown by the broken lines in Fig. 13, superimposed on the strap wrench, is to illustrate the position which my device takes, and particularly the working edges thereof, represented by line EE, relative to the circular object 116 when said device is in position wherein the said self-tightening principle comes into play. It can be seen from the Fig. 13 that line EE and, therefore, the working edges of my device, serve to preclude the operator from unwittingly placing the circular object in an inefficient position, as is possible with the common strap wrench. Furthermore, in light of the hereinabove discussion concerning angle "a and the relative placement of anchorage point A, it can be seen that the working edges also assist the operator, such as the housewife, in placing a jar lid of any commercial diameter with relation to elements of the device so that adequate torque-originated gripping takes place without overstressing the strap.

Another feature of my device is the fact that, coincident with the self-tightening action of the strap, there is a self-locking action created by friction of the strap against an element of the device which keeps the strap held tightly around the jar during the turning of the jar. This selflocking action occurs where the strap is squeezed between.

it is to be understood that various changes can be made in its construction by those skilled in the art without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. A strap wrench device comprising a flexible strap, a pair of parallel plates spaced apart and rigidly secured to each other to constitute a housing, the distance between said plates being in excess of the width of said strap, each of said plates having an edge parallel to an edge on said other plate, said parallel edges collectively constituting a working edge of said housing adapted for the placing of a circular object thereagainst, tangential thereto, said plates forming a space therebetween which is open at said edges and adapted for the passage of said strap edgewise therethrough on either side of said tangential point of contact when said circular object is against said working edge, a member rigidly positioned between said plates and having an arcuately-curved surface perpendicular to said plates, said surface beginning at said edges and extending inwardly therefrom, and having a convex portion facing outwardly, means for anchoring one end of said strap fixedly between said plates at a point inwardly from said opening in the said working edge, said strap passing out of and back into said opening to form a loop, and means for pulling the free end of said strap over said arcuate surface to position said loop firmly against a circular object placed tangentially against said working edge.

2. The apparatus of claim 1 wherein the said means for pulling the free end of said strap comprises a spindle rotatably positioned between said plates with its axis of rotation perpendicular thereto, the free end of said strap being fixed to the circumferential surface of said spindle, means for rotating said spindle, and said spindle being so positioned that as the strap is wound thereon dun'ng rotation of said spindle said strap passes over said arcuately-curved surface.

3. The apparatus of claim 2 with the addition of a plate fixed to said spindle whereby it rotates therewith and extending radially outward from the said spindle with the outer periphery of said radially extending portion being substantially concentric with the outer surface of said spindle, said plate being positioned adjacent to but rotatably free from the inner surface of either of the two plates of the said housing, and spaced apart from the other of said plates by a distance slightly in excess of the width of said strap, a ring shaped flange fixed circumferentially to said rotatable plate and extending axially inward therefrom, adapted to constitute a confining rotating wall for the coils of said strap when said strap is wound upon said spindle and unwound therefrom, the axial width of said flange being no greater than the width of said strap, and means for guiding said strap in an edgewise position into the annular space between said spindle and said flange when said spindle is being rotated to wind said strap thereon or to uncoil it therefrom.

4. The apparatus of claim 1 wherein said anchorage point of the fixed end of said strap is so positioned that when said circular object is positioned tangentially to said working edge of said housing and tangent to said arcuateshaped surface with the strap therebetween, said strap extends from its said anchor point through said opening in said working edge, thence about said circular object, and thence over said arcuate surface to within said housing, the apex of the angle formed between the straight line passing through said anchor point and the first point of tangency of the strap to said circular object and the straight line passing through the center of said circular object and the point of tangency where said strap leaves said circular object to pass over said arcuate-shaped surface lies on the side of said working edge toward said housing.

5. The device of claim .1 wherein said strap comprises a steel cable embedded in a jacket of plastic material having approximately the flexibility and strength of a flexible grade of polyvinyl chloride plastic material.

' 6. The device of claim 1 wherein said curved surface begins at a point rearwardly of said edges by a distance no greater than the thickness of said strap.

7. The device of claim 1 wherein said curved surface begins at a point rearwardly of said edges by a distance no greater than half the thickness of said strap.

8. The device of claim 5 wherein said cable comprises a ,4 inch steel cable.

9. A strap wrench device comprising a flexible strap, a pair of parallel plates spaced apart and rigidly secured to each other to constitute a housing, the distance between said plates being in excess of the width of said strap, each of said plates having an edge parallel to an edge on said other plate, said parallel edges collectively constituting a working edge of said housing, said plates form ing a space therebetween which is open at said edge, said strap passing from said space between said plates edgewise out of and back through said opening at said edge to form a loop adapted to be positioned around a circular object placed tangentially against said edges, a member rigidly positioned between said plates having a terminus 10 perpendicular to said plates and so positioned adjacent said edges and outside said loop of said strap that when said strap is pulled over said terminus to tighten said loop against a circular object placed tangentially against said edges within said loop, said strap is squeezed against said terminus.

10. The apparatus of claim 9 with the addition of means secured between said plates for anchoring one end of said strap fixedly between said plates a spindle rotatably positioned between said plates with its axis of rotation perpendicular to said plates, the free end of said strap being fixed to the circumferential surface of said spindle, and said spindle being so positioned that as said strap is wound thereon during rotation of said spindle said strap passes over the said terminus of said rigidly positioned member.

References Cited in the file of this patent UNITED STATES PATENTS 1,414,014 Genett Apr. 25, 1922 2,394,323 Menke Feb. 5, 1946 2,793,550 Robinson May 28, 1957