US3302691A

US3302691A - Folding door

Info

Publication number: US3302691A
Application number: US414676A
Authority: US
Inventors: George M Andrews; Charles W Gibson
Original assignee: Vega Industries Inc
Current assignee: HARROW SECURITIES Inc A CORP OF; Vega Industries Inc
Priority date: 1964-11-30
Filing date: 1964-11-30
Publication date: 1967-02-07
Anticipated expiration: 1984-02-07

Description

Feb 7 H967 G. M. ANDQEWS ETAL Sg FOLDING DOOR Filed Nov. 50, 1964. 7 Sheets-Sheet 1 ,f /3/6\:V 55/- l ISG 53 I O l k H2 |5 '11 L [l y 1 1s 1| ,l l I 1 y l lof l l i INVENTORS. GEORGE M. ANDREWS.

CHARLES. VJ. GISSON. m W

ATTORNEY.

7 Sheeis-Sheet 2 Feb. 7, 1967 e. M. ANDREWS ETAL FOLDING DOOR Filed Nov. :5o. 196A.

JNVENTORS.

GEURGE M, ANDREWS.

CHARLas w. GIBSON. BY f STTORNEY.

Feb 7. 3967 G. M. ANDREWS ETAL mm FOLDING DOOR Filed Nov. 30, 1964 7 Sheets-Sheet 3 INVENTORS. GEORGE Pil. ANDREWS. CHARLES W. GIBSON.

ATTORNEY.

Feh 7, 1967 G. M. ANDREWS ETAL E FOLDING DOOR 7 Sheets-Sheet 4 Filed NOV. 30, 1954 WIG. 4

,INVENTORS GEORGE M. NDREWS. CHARLES W. GIBSGN.

TTRNEY.

Feb 7, 967 G. M. ANDREWS ETAL @3102,93

FOLDING DOOR Filed Nov. 30, 1964 7 Sheets-Sheet 5 WIG. 5

IN VEN TORS.

GEORGE M. NDREWS. BY CHARLES W. GBSON.

ATTORNEY.

Feb 7, 3967 G. M. ANDREWS ETAL 3,302J59 FOLDING DOOR Filed Nov. 30, 1964 '7 Sheets-Sheet 6 l: I i

VIII III V INVENTORS. GEORGE M. ANDREWS. CHARLES W. GIBSON.

STTORNE?.

Feyo 7, i967 e.. M. ANDREWS r-:TAL 393029593 FOLDING DOOR Filed Nov. 30, 1964 '7 Sheets-Sheet 7 R" 2;.. @im 25 m; L@ n IN VEN TORS. GEORGE M. ANDREWS. BY CHARLES W. GIBSON.

TTORNEY United States Patent Oiltice 3,302,691 Patented-Feb. 7, 1967 3,302,691 FOLDING DOOR GeorgeM. Andrews, Syracuse, N.Y., and Charles W.

Gibson, Bloomingdale, Mich., assiguors to Vega Industries, Inc., Syracuse, N.Y., a corporation of New vitork Filed Nov. 30, 1964, Ser. No. 414,676 7 Claims. (Cl. 160-206) This invention relates to a folding door structure. Such structures consist of at least one pair of panels hinged together along their vertical edges, one panel having a hinge structure at, or adjacent to, its free vertical edge, and Athe second panel being provided at, or adjacent to, its free vertical edge with guide rollers movable in upper and lower tracks. For door openings of substantial width, a second pair of panels may be employed. Such door structures are used extensively for closures for door openings in the interior of buildings, for example, closet door openings. Such door structures have Ithe advantage in requiring less than one-half of the swing space occupied by conventional doors. However, prior folding doors embodied a relatively heavy construction, which necessitated the services of professionalmechanics to install the doors, and often the door structures became warped or twisted causing them to bind and become otherwise diicult to operate.

This invention has an object a folding door structure embodying a light weight structure which is particularly economical to manufacture, which is particularly easy to open and close, and which will not bind even under adverse conditions of mis-use.

The invention has as a further object a folding door structure wherein ythe mechanism on which the doors are hinged and guided is conveniently adjustable to effect proper alignment of the door panels and ease of operation, even though the door opening is out of square, which is often the case.

The door structure of our invention may be shipped in compact form and quickly installed by a non-skilled person by the employment of only a screwdriver.

The invention consists in the novel features and in the combinations and constructions hereinafter set forth and claimed.

In describing this invention reference is had to the accompanying drawings in which like characters designate corresponding parts in all the views.

FIGURE 1 is an elevational view of the inner side of a two-panel door embodying our invention and including the contiguous portion of the door frame.

FIGURE 2 is a view similar to FIGURE 1 with the door panels in full open position and illustrating the upper track inclining upwardly to the left, due to the out of square condition of the door opening.

FIGURE 3 is an enlarged view of the upper right-hand portion of the structure shown in FIGURE 1.

FIGURE 4 is an enlarged view of the lower right-hand portion of FIGURE 1.

FIGURE 5 is an enlarged view of the upper left-hand portion of FIGURE 1.

FIGURE 6 is an enlarged view of the lower left portion of FIGURE 1.

FIGURE 7 is a view taken on line 7 7, FIGURE 4.

FIGURE 8 is a View taken on line 8 8, FIGURE 3.

FIGURE 9 is a view taken on line 9 9, FIGURE 5.

FIGURE l is a view taken on line lil-10, FIGURE 6.

FIGURE ll is a perspective view of the bracket structure for the lower pintle pin.

FIGURE l2 is a view taken on line 12 12, FIGURE 3.

FIGURE 13 is a view taken on line 13 13, FIGURE l.

The door structure includes at least one pair of panel members designated generally 10, 11. Each of these members consists of a rectangular frame formed of tubular side members 13, and tubular top and bottom cross members 14. In the structure shown, the

tubular members

13, 14 are formed of sheet metal bent up to form a tube, rectangular in cross section, see FIGURES 7-10. The exterior or front side of these members is bent outwardly and formed with a ange 17 spaced from the sides 16. The inner side 18 is bent at right angles to form the outer wall 19 of the tubular member, which in turn, is formed with a ilange Ztl overlying the flange 17, and is then bent inwardly over the edge of the flange 17. This construction provides a channel about the margin of the outer side of the tubular frame member for the reception of the perimetric margin of a facing member 22, see FIGURE 7. A facing member 23 of greater thickness may be formed about its edge with aslot to receive the

flanges

17, 20, as shown in FIGURE 8. This arrangement provides a portion of the facing member 23, of reduced thickness, extending into the channel formed by the spacing between the side Wall 16 of the tubular member and the

flanges

17, 20.

The tubular members making up the frame of each panel are secured together at the upper and lower corners of the panels by -triangular-shaped gusset membersV 15. The gusset members 15 are formed of sheet metal and are attached to the

tubular members

13, 14 as by spot welding. Each gusset is formed with a rectangular opening 25. A portion of the metal removed from the opening 25 is bent inwardly to form a ange 26, which is pierced to form two

extrusions

27, 28, each of which is form-ed with an aperture, the axes of which extend vertically or parallel to the side members 13. The end members 14 areformed with apertures aligned with the apertures in the

extrusions

27, 28.

The inner, upper, and lower corners of the panel frame structures are also joined by triangular gussets 31. The gussets 31 are not formed with the openings 25, but are formed along their abutting edges with ear portions to form a hinge 32. One or more hinges are also attached to the inner side members 13. With this arrangement, the panel 1G is hingedly joined to the panel 11.

The door structure further' includes an upper track member 35 secured to the header 36 of the door opening as by screws 37. There is a lower track member 38 mounted on the sill of the door opening as by screws 39. With the door installed, as shown in FIGURE l7 the panel 11 is hinged or pivoted for movement about a vertical axis adjacent the jam 40 of the door opening. The panel 10 is provided adjacent its outer free edge with guide rollers movable in the upper and

lower tracks

35, 38. The pivot l mounting for the panel 11 includes an upper pintle pinv 43, slidably mounted inthe upper gusset memberlS of the panel 11. This pin is slidably mounted in the aperture of the extrusion 28, and the corresponding aperture in the upper cross member 14, see FIGURES l, 3, and 8. The' pin 43 is provided with a collar or stop member 47, and a helical compression spring 48 is interposed between the interned flange 26 of the gusset member 15, and the collar I 47, and acts to urge the pin yieldingly upwardly. The upper end portion 44 of the pin 43 is of reduced diameter and extends into a laterally extending flange 45 of a bracket 46 mounted in the upper track 35.

VThe upper track member 35 is'formed with depending side walls 5t), 51 to provide a roller receiving slot. The side wall 5t) is formed along its lower edge with an inwardly extending ange 52, see FIGURE 8. The side wall 51 is formed with an inwardly extending ilange 53 extending in a plane above the flange 52. The bracket 46 is formed of sheet metal and has a top wall 55 and depending

side walls

56, 57. The side wall 57 is positioned on the flange 53 and the side wall 56 is positioned .on the flange 52. The bracket has an end wall 60, and the flange i 45, in which the pivot pin 43 is mounted, is a continuation of a depending end wall 60. The top Wall 55 of the bracket 46 is formed with a punched extrusion 61, which is threaded to receive a screw 62, see FIGURE 3. When the screw is threaded through the top wall of the bracket, t-he end of the screw engages the top wall `of the track 35 moving the

sides

56, 57 of the bracket into engagement with the

flanges

53, 52 of the track. This arrangement provides for adjustment of the bracket lengthwise of the track 55.

There is a pintle pin 67 slidably mounted in the lower corner gusset 15, and extends through the aperture in the extrusion 28 thereof and through an aligned aperture in the lower cross member 14, whereby the pintle pin 67 is arranged in axial alignment with the pintle pin 43. The lower end of the pin 67 extends through an aperture 70 formed in a bracket 71 positioned in the lower track member 38. The aperture 70, see FIGURE ll, is of such diameter as to provide clearance for the pin 67. A retaining plate 73 is positioned lagainst the undersurface of the top wall of the bracket 71, and is provided with an aperture 74 of diameter comparable to the aperture 70. The aperture 74 communicates with a slot 75. The lower end portion of the pin 67 is formed with a necked down portion 80, the diameter of which is slightly less than the width of the slot 75 in the retaining plate. The retaining plate has a threaded aperture 81 to receive a screw 82 which extends through an elongated opening 83 in the top wall of the bracket 71. With this arrangement, the retaining plate 73 can be moved lengthwise of the bracket and track 38 to bring its aperture 74 in registration with the aperture 70 in the bracket to permit insertion of the pintle pin 67 Thereupon, the retaining plate 73 is shifted to the left, FIGURE ll, so that the necked down portion 80 is positioned in the slot 75 and, accordingly, the pintle pin is restrained from vertical movement.

The lower track member 38 is formed with inclined side walls 85 having, at their upper edges, inwardly extending anges 86. The bracket 71 is formed along each side edge with an inclined flange 87. When the bracket is inserted in the lower track member 3S, a screw 88 is threaded into a counter-sunk aperture 89 in the top wall of the bracket, the lower end of the screw engages the bottom wall 90 of the track to clamp the sides 87 `of the bracket against the sides of the track. This arrangement, as in the case of the upper pintle bracket, provides for adjustment of the bracket along the track 38.

The pintle pin 67 is provided with threads, the major portion of its length from the upper end downwardly. A collar 93 is threaded on the pin 67 and is held in adjusted position by a set screw 94. The collar 93 engages the ange 26 of the gusset 15. A helical compression spring 95 is interposed between the outer wall of the lower cross member 14, and the collar 93 serves to yieldingly maintain the stop member 93 against the ange 26 of the gusset 15, as shown in FIGURE 7. The purpose of the stop member 93 is to vertically position the panel frame 11 to provide proper clearance between the lower edge thereof and the lower track 38. This adjustment is made by loosening the set screw 94, and rotating the pin 67. To make such operation convenient, the upper end of the pin is provided with a screw driver slot 98.

With the structure described, the panels 10, 11 are pivotally mounted in the door opening, and the panel 10 is hinged to the panel 11.

As previously stated, the panel is provided adjacent its free edge with upper and lower guide members to properly guide the panels during opening and closing of the door structure. Referring now to FIGURES 1, 6, and 10, a pin 100 is slidably mounted in the aperture of the extrusion 27 in the ange 26 of the lower gusset member 15, the pin extending through an aligned aperture in the wall 19 of the lower cross member 14 of panel 10. The lower end of the pin 100 is necked down as at 101, and a bottom roller 102 is journalled on the necked down portion 101 of the pin, the roller being positioned in the lower track member 38. The pin is provided with a stop collar 103, and a compression spring 104 is interposed between this collar and the flange 26 of the gusset, thereby urging the pin downwardly against the roller 102 and the latter against the lower inclined walls 105 of the lower track.

Referring now to FIGURES 1, 5, and 9, there is a pin slidably mounted in the upper left gusset member 15 of the panel 10, this pin also extending through the aperture of the extrusion 27 in that gusset, and through the aligned aperture at the upper cross member 14. There are a pair of rollers 111, 112 joumalled on the upper end of the pin 110, and the pin is restrained against downward movement by a head 113. The lower portion of the pin 110 is threaded to receive a stop collar 114, similar to the collar 93. A compression spring is interposed between this collar, and the flange 26 of the gusset member, and serves to yieldingly urge the panel 10 upwardly. The upper roller 111 engages the upper flange 53 of the upper track, and the lower roller engages the lower ange 52. The collar 114 is adjusted axially along the pin 110 to a position where the spring 115 will give adequate support to the panel 10. The purpose of the spring 104, encircling the lower roller pin 100, is to maintain the lower end of the pin in engagement with the lower roller 102 under slight pressure, and to prevent any rattling of the door during the opening and closing thereof. Spring 115, in addition to providing a supporting force for the panel 10, also functions to prevent any looseness or play between the pin 110 and the door panel and between the rollers 111, 112 and the upper track member.

The mounting arrangement of the roller pins 100, 110 is an important feature of our invention. In actual practice, Imore often than not, door openings are not framed perfectly square, and with the header extending parallel to the sill of the opening. In other door structures of this type, it then becomes necessary to shim the upper track in order to bring it in parallel relation to the lower track. With our door structure, the header and sill can be out of parallelism to a substantial degree, yet the upper track may be xedly secured directly to the header. This arrangement permits vertical sliding movement of the pin 110 during the opening and closing of the door when the door opening is out of plumb. For example, in FIGURE 2, the upper track member 35 slants upwardly to the left, the horizontal being indicated by the dotted line 117. In a situation of this kind, the roller -pin 110 simply slides up and down during the closing and opening of the door, and without causing any binding during the operation of the door.

Referring to FIGURE 9, it will be observed that the lateral spacing between the

track anges

51, 52 is such, relative to the diameter of the rollers 111, 112, that there is a clearance between the side wall 51 and the lower roller 112, and a clearance at 121 between the roller 111 and the side wall 50. In other words, the rollers 111, 112 engage only their

respective flanges

53, 52 and do not engage the opposite side wall of the track. This permits free rotation of the rollers 111, 112 in both directions, along the track, and this is true even `though considerable lateral pressure is exerted against the door panels.

With the construction described, the door structure is adapted to be shipped in a package form including the panels 10, 11, the upper and lower track sections, and the panel hanging hardware described. A rubber bumper is positioned in the upper track 35, and a similar bumper 131 is positioned in the lower track 38, together with the roller 102. The lower pintle bracket 71 is also positioned in the lower track member, and the upper pintle bracket is positioned in the upper track member. The pintle pins 43, 100 are mounted in the panel 11. The roller pins 67, 100 are mounted in the panel 10. The rollers 111, 112 yare mounted on the pin 110.

The door structure is installed by mounting the upper and

lower tracks

35, 38 on the header and sill of the opening. The panel assembly is then angled to insert the rollers 111, 112 through an access opening 133 formed in the upper track 35 in proximity to the end thereof, in which the pintle pin 43 will be mounted. At this time, the upper pintle bracket is moved toward the adjacent opening jam 40. When the rollers 111, 112 have been thus insertedinto the upper track, the rollers are moved toward the center of the track. The panel 11 is then manipulated to bring the lower pintle pin 67 into the aperture 70 of the Alower bracket and the plate 73 moved and locked in place by screw 82 to captivate the lower end of the pintle pin 67. Y

The upper pintle bracket is then moved in the upper track to locate the aperture in the flange 4S the same distance from the door jam 40 as the lower pintle pin 67. The upper Ipintle pin 43 is then inserted into the upper bracket. The door structure is shipped with a retaining pin 135 inserted through an aperture 136 in the pin 43, at which time the aperture 136 is below the gusset ange 26. The retaining pin 135 is shown in dotted outline, FIGURE 3. Accordingly, all that is necessary to do is to remove the pin 135, and the compressed spring 48 moves the pintle pin 43 upwardly into engagement with the upper pintle bracket.

The lower 4guide roller 102, which in shipment was captivated in the lower track section by the lower bracket and the rubber bumper, is moved along the track to the left in the drawings so that the pintle pin 100 may be positioned over it. This pintle pin is also provided with an aperture 138 to receive a retaining pin on the upper side of the gusset flange 26. Accordingly, by removing that retaining pin, the spring 104 moves the pin 100 downwardly into engagement with the lower roller 102.

The door panels may then be moved laterally to center the same in the door opening by adjusting the upper and lower pintle brackets in the upper and lower tracks, and when this adjustment is eifected, the upper bracket is locked in place by screw 62, and the lower bracket is locked in place by screw 88. When the upper bracket is secured in proper position, it -covers the access cutout 133 in the top track so that the rollers 111, 112 cannot escape.

The door can be adjusted for height by simply turning the lower pintle pin 67 inthe stop member 93. When the height adjustment has been effected, the set screw 94 is tightened.

As the weight of the panels 10, 11 are increased substantially, as by mounted glass mirrors on the iinished panels 22, 23, the stop nut 114 may be threaded upwardly to cause the spring 115 to exert a greater force on the gusset flange 26; these various adjustments being made to effect easy and noiseless operation of the panels during the opening and closing thereof.

The

rubber bumpers

130, 131 serve to provide for a silent closing of the panels and, also, to position the panels under a slight yielding pressure when the panels are moved to closed position in order to make certain that the panels remain in closed position. In this connection, it will be noted that the -access of the pintle in hinges 32 is located rearwardly of the plane of the pintle pins and roller pins, see FIGURE 13. With this arrangement, the panels close snap fashion, the panels forming a slight-ly over the center toggle arrangement so that the door panels remain in closed position.

The flange 140 on bracket 46 is engaged by the rollers 111, 112 when the door is actuated to open position, the flange 140 serving as a bumper stop, see FIGURE 2.

What we claim is:

1. A folding door structure for a door opening, an upper track member ixedly mounted to the header in the door opening and extending between the jams thereof, said track member being formed with a roller receiving slot having inwardly extending side flanges extending in spaced parallel relation, a lower track member formed with a roller receiving slot and being iixedly mounted to the sill of the opening and extending between the jams thereof, a pair of first and second panel mem-bers hingedly joined along their vertical edges and being of vertical dimension for insertion in said opening between said track members, the rst of said panels being provided with vertically aligned upper and lower pintle pins extending from the upper and lower edges of said rst panel in spaced relation to said hinged joint, the outer ends of said pins being journalled in said upper and lower track members, said upper pintle pin being axially slidable in said irst panel, spring means acting on said pin to yieldingly urge the same upwardly, said lower pintle pin having a stop collar member adjustable axially of the pin for engaging said first panel for the support of said first panel by said lower pintle pin, upper and lower roller pins mounted in said second panel of said pair in spaced relation to said hinged joint, said lower roller pin having a roller journalled thereon for movement along the slot in said lower track member, said upper roller pin having a roller journalled thereon for movement along the flanges of said upper track member, means restraining downward movement of said upper roller pin relative to the roller journalled thereon, said upper and lower roller pins being axially slidable in said second panel.

2. A folding door structure as defined in claim l, wherein said lower pintle pin is slidably mounted in the lower edge structure of said rst panel and a flange thereof spaced above said lower edge structure, said stop collar member being positioned on said lower pintle pin below said ange, and spring means interposed be-tween said lower edge structure and said stop collar member and operable to yieldingly press said stop member against said flange.

3. A Ifolding door structure as set forth in claim 1, wherein said stop collar member is threaded on said lower pintle pin and means is provided for interlocking said stop member to said pin.

4. A folding door structure according to claim 1, wherein said ange is cooperable with said stop collar member to restrain the same against rotation relative to said lower pintle pin.

5. A folding door structure as set forth in claim 1, wherein a stop collar member is mounted on said upper roller pin and being adjustable axially thereof, a spring interposed between said stop collar member and said second panel for yieldingly supporting the same.

6. A folding door structure as set `forth in claim 1, wherein said upper roller pin is slidably mounted in the upper edge structure of said second panel and in a ange thereof positioned 'below said upper edge structure, a stop collar member carried fby said upper roller pin, and a spring interposed -between said stop collar member and said flange and operable to yieldingly support said second panel on said upper roller pin.

7. A folding door structure for a door opening, an upper track member iixedly mounted to the header of the door opening and extending between the jams thereof, said track member having spaced apart, vertically disposed side walls, a roller supporting ilange formed on the inner surface of each of said side walls, said tlanges extending in spaced parallel relation in both the horizontal and vertical plane, a lower track member formed with a roller receiving slot and being xedly mounted to the sill of the opening and extending between the jams thereof, a pair of iirst and second panel members hingedly joined along their vertical edges and being of vertical dimension for insertion in said opening between said track members, the rst of said panels being provided with a pair of vertically aligned pintle pins extending from the upper and lower edges of said panel in spaced relation to said hinged joint, the ends of said pins being journalled in said upper and lower track members, upper and Ilower roller pins vertically mounted in the second panel of said 7 pair in spaced relation to said hinged joint, said lower roller pin having a roller journalled thereon for movement along the slot in said lower track member, said upper roller pin having a pair of rollers journalled thereon in axially spaced apart relation eomplemental to the Vertical spacing `between said anges in said upper track member for movement along the anges, respectively, means restraining downward movement of said upper roller pin relative to the rollers journalled thereon, the rollers journalled on said upper pin being of substantially equal diameter, said roller receiving flanges Vbeing spaced inwardly from the contiguous side wall of said upper track member, whereby said rollers journalled on said upper pin do not engage the side Wall of said upper track member, opposite to the flange supporting each said roller.

References Cited by the Examiner UNITED STATES PATENTS 1,444,349 2/1923 Leeds 160-196 2,860,701 11/1958 Wood et al. 160-199 2,943,675 7/1960 Ford 160-206 3,019,836 2/1962 Leigh 160-199 3,042,960 7/ 1962 Spork.

3,205,982 9/1965 Chimienti 189-46 HARRISON R. MOSELEY, Primary Examiner.

D. L. TAYLOR, Assistant Examiner.

Claims

1. A FOLDING DOOR STRUCTURE FOR A DOOR OPENING, AN UPPER TRACK MEMBER FIXEDLY MOUNTED TO THE HEADER IN THE DOOR OPENING AND EXTENDING BETWEEN THE JAMS THEREOF, SAID TRACK MEMBER BEING FORMED WITH A ROLLER RECEIVING SLOT HAVING INWARDLY EXTENDING SIDE FLANGES EXTENDING IN SPACED PARALLEL RELATION, A LOWER TRACK MEMBER FORMED WITH A ROLLER RECEIVING SLOT AND BEING FIXEDLY MOUNTED TO THE SILL OF THE OPENING AND EXTENDING BETWEEN THE JAMS THEREOF, A PAIR OF FIRST AND SECOND PANEL MEMBERS HINGEDLY JOINED ALONG THEIR VERTICAL EDGES AND BEING OF VERTICAL DIMENSION OF INSERTION IN SAID OPENING BETWEEN SAID TRACK MEMBERS, THE FIRST OF SAID PANELS BEING PROVIDED WITH VERTICALLY ALIGNED UPPER AND LOWER PINTLE PINS EXTENDING FROM THE UPPER AND LOWER EDGES OF SAID FIRST PANEL IN SPACED RELATION TO SAID HINGED JOINT, THE OUTER ENDS OF SAID PINS BEING JOURNALLED IN SAID UPPER AND LOWER TRACK MEMBERS, SAID UPPER PRINTLE PIN BEING AXIALLY SLIDABLE IN SAID FIRST PANEL, SPRING MEANS ACTING ON SAID PIN TO YIELDINGLY URGE THE SAME UPWARDLY, SAID LOWER PINTLE PIN HAVING A STOP COLLAR MEMBER ADJUSTABLE AXIALLY OF THE PIN FOR ENGAGING SAID FIRST PANEL FOR THE SUPPORT OF SAID FIRST PANEL BY SAID LOWER PINTLE PIN, UPPER AND LOWER ROLLER PINS MOUNTED IN SAID SECOND PANEL OF SAID PAIR IN SPACED RELATION TO SAID HINGED JOINT, SAID LOWER ROLLER PIN HAVING A ROLLER JOURNALLED THEREON FOR MOVEMENT ALONG THE SLOT IN SAID LOWER TRACK MEMBER, SAID UPPER ROLLER PIN HAVING A ROLLER JOURNALLED THEREON FOR MOVEMENT ALONG THE FLANGES OF SAID UPPER TRACK MEMBER, MEANS RESTRAINING DOWNWARD MOVEMENT OF SAID UPPER ROLLER PIN RELATIVE TO THE ROLLER JOURNALLED THEREON, SAID UPPER AND LOWER ROLLER PINS BEING AXIALLY SLIDABLE IN SAID SECOND PANEL.