US3603556A

US3603556A - Pivoted member assembly

Info

Publication number: US3603556A
Application number: US516184A
Authority: US
Inventors: Virgil L Frantz
Original assignee: Graham White Sales Corp
Current assignee: Roanoke College; Graham White Sales Corp
Priority date: 1965-10-22
Filing date: 1965-10-22
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07

Abstract

This invention relates to pivoted member assemblies and has as its primary object the provision of an improved pivoted member assembly in which the pivoted member can be held by friction in a selected position despite vibrations to which its mounting is exposed in service.

Description

inventor Virgil l... lFrnmz Salem, Wn. Appl. No. llJ-ii Filed Urt. 22, i985 Patented Sept. 7, 197i Assignee Graham-White Sales Corpomtion Salem, Vm. Continumtion oi applition Ser. No. A3,(36, .lluly 115, i960, now almndolmed.

PIT/@TMB MEMBER ASSEMBLY 5 Elimina, l5 Drawing Figs.

IUE. CII 2A8/4l79, 16/140, 248/289 limit. CII Bom ll/ii Tied of Smil-elli 16/40, 151, 168; 88/86, 87, 92, 93, 96, 97, 98; 20/16; 189/46; 98/106; 248/479, 289

[5 6] Reierences Cited UNlTED STATES PATENTS 90,330 5/1869 Wolters 16/168 735,481 8/1903 Ek 16/140 743,279 l H1903 Haycock 16/168 2,146,391 2/l939 Anderson l6/l40 2,698,958 I/l955 Adams 16/140 FOREIGN PATENTS 105,113 4/1917 Great Britain 16/14 Primary Examiner-David Schonberg Assistant Examiner-Ronald J. Stern Attorney-Wilmer Mechlin ABSTRACT: This invention relates to pivoted member assemblies and has as its primary object the provision of an irnproved pivoted member assembly in which the pivoted member can be held by friction in a selected position despite vibrations to which its mounting is exposed in service.

PATENTE SEP 7197i sum1 0F 3 FIG. l

FIG. 3

FIG. 2

Inventor: Virgili L. Frantz FIG. 4

his Attorney PMENTED SEP 1 :en

SHEEI 2 BF 3 PIG.. 6

lnve Mor: Vi'yqgl L. Franw his Attorney,

PIVOTEID MEMBER ASSEMBLY This application is a continuation of my copending application Ser. No. 43,036, filed July l5, i960 now abandoned.

Another object of the invention is to provide a friction mounting for a pivoted member whereby play in the pivotal connection between the member and the support on which it is mounted is effectively eliminated.

An additional object of the invention is to provide a friction mounting for a pivoted member which is readily adjustable in the friction restraining pivoting of the member to meet the requirements of a particular installation.

A further object of the invention is to provide a pivoted member assembly wherein the pivoted member has a framed glass or like plate, the frame of which is readily disassemblable for replacement of the plat but is blocked from accidental disassembly by the pivotal mounting.

Another object ofthe invention is to provide in a pivoted member assembly a disassemblable frame, the disassembly of which is facilitated by one or more parts capable of backing itself` off from another part as it is disconnected therefrom.

Another object of the invention is to provide a friction mounting for a pivoted member which not only is adjustable in friction but is proof against change in the adjustment by either service vibrations or pivoting of the member.

A feature of the invention is the provision as a pivot of an adjustable friction mounting for a pivoted member, of a tapered metal or other rigid pin fitting into a correspondingly tapered socket in a bushing of brake lining or like material which effectively prevents the buildup of vibrations in the member.

Other objects and features of the invention will appear hereinafter in the detailed description, be particularly pointed out in theappended claims and be illustrated in the accompanying drawings in which:

FIG. l is a side elevational view of a preferred embodiment of the pivoted member assembly of the present invention;

FIG. 2 is a rear end elevational view of the assembly of FIG. Il;

FIG. 3 is a front end elevational view of the assembly of FIG. l;

FIG. 4 is a plan view of the assembly of the preceding figures;

FIG. 5 is a fragmentary vertical sectional view on an enlarged scale, taken along lines S-S of FIG. 4l;

F IG. 6 is a fragmentary horizontal sectional view taken along lines 6 6 of FIG. S;

F IG. '7 is a fragmentary horizontal sectional view taken along lines 7-7 of FIG. 5;

FIG. d is a fragmentary horizontal sectional view taken along lines of FIG. 5;

FIG. 9 is a fragmentary horizontal sectional view taken along lines 9-9 of FIG. S;

FIG. l is a fragmentary vertical sectional view taken along lines lltl-llll ofFIG.

FIG. lll is a side elevational view of another embodiment of the pivoted member assembly of the present invention;

FIG. l2 is a rear end elevational view of the assembly of FIG. Il;

FIG. llll is a horizontal sectional view on an enlarged scale taken along lines l3-ll3 of FIG. Il;

FIG. Ml is a fragmentary horizontal sectional view on the scale of FIG. 13, taken along lines 14-14 of FIG. Il; and

FIG. )l5 is a fragmentary horizontal sectional view on the scale of FIG. ll3, taken along lines ll5-l5 of FIG. lll.

Referring now in detail to the drawings in which like reference characters designate like parts, the improved pivoted member assembly of the present invention may be used to provide a windshield wing, a front or rear quarter window, a rearview mirror or any other member designed for pivotal mounting on part of a vehicle or other support and to be held by friction in any of a plurality of angularly related positions in which it is set, despite vibration of thesupport in service. As exemplary of the invention, the assembly of each of the illustrated embodiments is of a type particularly suited for use as a windshield assembly on a locomotive, the as sembly of the second embodiment also including, as a subassembly, an exemplary rearview mirror assembly.

Considering first the embodiment of FIGS. l-llI), the pivoted member assembly there illustrated is comprised of a windshield wing or other pivoted member 1, which may be of one piece or unitary, but ordinarily will include a transparent or mirror plate 2 of glass or other suitable material and a frame 3 mounting and partly or entirely surrounding or framing the plate. Made of anodized aluminum, stainless steel or other material suitable for the particular environment in which it is to be used, the illustrated frame 3 is constructed of a plurality or, more exactly, a multiplicity of pieces or parts detachedly or removably connected to each other to facilitate application or removal of the plate 2.

In this first embodiment, the frame 3 is open at the rear and formed of three pieces, parts or elements, one a vertically extending frontpiece 4 and the others horizontally extending upper and lower, top and bottom or

endpieces

5 and 6, respectively, the latter overlying and embracing or including the extremities of the frontpiece. ln assembled relation the

several pieces

4, 5 and 6 are interrupted along their inner edges 7 by a continuous channel or groove 8 in which the plate 2 seats or is received, the groove preferably having a rubber or like resilient lining or padding to protect the plate against breakage and being partly closed at the rear by intumed or instanding rear legs 9 of the upper and lower pieces. To maintain or hold them against angling relative to the frontpiece 4, each of the upper and

lower pieces

5 and 6 preferably has a tongue and groove or like antirotational joint or interfit l0 between its intumed or instanding front leg Il and the adjoining or contiguous end or extremity l2 of the frontpiece. The releasable interlock or attachment between the

endpieces

5 and 6 and the frontpiece 4 is here provided by a pair of bolts 13, each slidably received or fitting in a bore I4 in the front leg l1 of one of the end pieces and threadedly engaged or received in an axially aligned or concentric bore l5 in the adjoining end l2 and extending longitudinally of the frontpiece.

So mounting or supporting the plate 2, the pivoted member ll is pivotally mounted on a window frame or other suitable part (not shown) of the vehicle or other support to which it is applied by a pair of coaxial pivots I6 which usually will be axi ally spaced and, here, conveniently connect to the

endpieces

5 and 6 above and below and in longitudinal alignment with the frontpiece 4. Each of these pivots I6 has as its essential components a pivot pin or stud of stainless steel or other suitable rigid material and one or more friction bushings, plugs or blocks ll7, each having an inwardly tapered or conical and preferably frustoconical recess, aperture or seat I8 rotatably receiving or seating a correspondingly outwardly tapered end 19 of the associated pivot pin. Each bushing 17 surrounds or encircles and is of greater depth than the received end 19 of the associated pin, thus separating or spacing and so serving as the only contact or connection between the pin and the member or part in which the bushing is socketed.

Any play in the pivotal connection between a windshield wing or like pivoted member and the part on which it is mounted will cause the member to vibrate excessively under forces on or transmitted to it and such vibration in turn will produce rapid wear in the connection and further aggravate the condition. Play is necessary in a pivotal connection in which there is metal-to-metal contact between the relatively pivoting elements to avoid galling or seizing of the metal, but in the connection of this invention play is prevented by the tapered fit between each pin and bushing, by the containment of the pin ends in the associated bushings and by making the bushings of a material combining toughness and resilience with a high coefficient of friction. Of the materials possessing these characteristics, brake lining material is preferred, its high frictional coefficient and resiliency accommodating a wide range of adjustment in the frictional drag or resistance to pivoting of the pivoted member, while its toughness and wearresistance assure long service life.

While each of the pivots 16 includes a pivot pin and a friction bushing, the pivots preferably are not identical. lnstead, the lower or bottom pivot pin 20 preferably is a double-ended pin, the opposite tapered ends 19 of which each fits in the correspondingly tapered aperture or seat 18 in the friction bushing 17, Of the two bushings 17 used in the lower pivot 16, one is carried by or connected or attached to the pivoted member l and the other is correspondingly associated with an adjoining part (not shown) of the vehicle or other support (not shown) on which the assembly is pivotally mounted. Depending on the installation, the support-attached bushing of the lower pivot may be mounted directly on the support part. However, in the exemplary installation in which it is used as a locomotive windshield wing, the assembly, instead of being mounted within a frame bounding a window opening, as are the quarter windows of automobiles, is designed to be attached to the locomotive cab outside the opening. For such in stallation, the assembly includes not only the pivoted member l and its pivots 16 but also upper and lower mounting brackets 2l and 22, each boltable or otherwise removably attachable exteriorly to a corner post or like part (not shown) at a side of the windshield (not shown).

Conveniently, the lower mounting bracket 22 carries the lower friction bushing of the lower pivot in an upwardly opening socket or pocket 23 which conforms in cross section to the bushing and, for ready application and removal of the latter, preferably is of cylindrical or other uniform cross section, It also is preferred that the lower mounting bracket 22 have a bore or aperture 24 extending through it and coaxial or concentric with the lower pivot pin 20, so that, in case of need during disassembly, that pivot pin can be dislodged from the lower bushing by being tapped from below. The upper bushing of the lower pivot, as well, preferably is seated in the member by which it is carried and thus, here, seats in a socket or pocket 25 in and opening downwardly from the lower endpiece 6 of the frame 3, this socket or seat, like the confronting socket or seat 23 in the lower bracket 22, snugly fitting its bushing, with the latter preferably cylindrical or of other uniform cross section to facilitate its removal. While accessible from below through the bore 24 in the lower bracket 22, the lower pivot pin 20 is not so accessible from above and, to facilitate its removal from the upper bushing, thus preferably has, substantially midway of its ends, about its, here, cylindrical midportion 26, an annular flange 27 through which it can be pried from the upper bushing.

One of the pivots 16, here the upper pivot, is designed not only to serve as a pivot but also to enable the friction restraining swinging of the pivoted member 1 to be varied to suit the needs of a particular installation. Although this might be accomplished with a double-ended pivot pin such as that here used in the other or lower pivot, it is preferred that the upper pivot pin 28 have a single tapered end 19 and that the friction bushing for that pivot seat or fit snugly in an upwardly opening socket, pocket or seat 29 of corresponding configuration in the upper endpiece of the frame 3. ln lieu of a second tapered end, the pivot pin 28 has as its opposite end an out-ofround, preferably square or rectangular head 30 which slidably fits or seats in a correspondingly rectangular or other wise out-of-round slot 31 in the upper mounting bracket 21. Opening downwardly and conveniently extending horizontally through the upper bracket 21, the slot 3l permits the upper pivot pin 28 to be slid or shifted axially relative to the bracket, while enabling the bracket to prevent rotation of the pin incident to pivoting ofthe pivoted member l. This nonrotatable connection between the upper pivot pin 28 and upper mounting bracket 21 effectively prevents any rotational or pivotal forces from being transmitted through the pin to an adjusting or capscrew 32 threaded from above through the upper bracket 21 in axial alignment or concentric with the pin and bearing against or engaging the upper surface or end 33 of the head 30, the adjusting screw 32, to hold the pin in correct axial alignment, preferably has a necked or relatively narrow cylindrical tip or lower end portion 34 fitting in a correspondingly configured cavity 35 in the confronting end of the head 30 and itself has a hex or like head 36 suitable for wrench actuation. Preferably, the adjusting screw 32 is lockable against rotation by a lock nut 37 encircling its threaded stem 38 above the bracket 21.

Constructed in the above manner and with its several friction bushings 17 identical for interchangeability, the pivoted member assembly is enabled on actuation of the adjusting screw 32 to vary the penetration of the several tapered ends 19 of the

pins

20 and 28 and, by virtue of the wedging action derivable from the taper of these ends, control the friction engendered between the pivot pins and the friction bushings. Depending on the particular installation, the adjustment of the friction in the mounting may be varied from one extreme at which the pivoted member will pivot at the touch of a finger to the other in which the member is actually locked against rotation, This, coupled with the ability of both pivots to be playfree, tight or snug over the range of adjustment and thus prevent a buildup of vibrations in the pivoted member, permits the pivoted member to be held against vibration or other movement relative to its support in any pivoted position in which it is set, despite vibrations in the support and any wind or like pressure to which it may be subjected n service.

lt was mentioned earlier that the bolts 13 by which the upper and lower endpieces 5 and 6 of the frame 3 are connected to its front piece 4 preferably are concentric with each other and extend longitudinally of the frontpiece. This preferred construction has purpose in facilitating disassembly of the frame 3 if, in addition, the bolts 13 are concentric with the pivotal axis of the pivoted member 1, are inset in the front legs 1l of the endpieces S and 6 inside the bushing-receiving

sockets

25 and 29 therein and have their heads 29 of larger diameter or cross section than the inner ends of the apertures 18 in the friction bushings 17 fitting snugly in those sockets. Rotatable in the bores 14 in the front legs l1 and with their heads 39 countersunk into the legs inside the bushing-

receiv ing sockets

25 and 29, the connecting bolts 13 are releasably held against axial movement relative to the end pieces by engagement of their heads by the associated snug-fitting bushing 17. Also, while the apertures in the bushings are of less minimum cross section than the heads 39 of the bolts, they are of ample crosssection to receive an Allen" wrench or like means (not shown) for turning the bolts. Consequently, once it has been removed from its pivotal mounting, the frame can be disassembled by backing off the connecting bolts 13 without removing the associated friction bushings 17 and the latter, by holding the bolts against axial displacement relative to the

endpieces

5 and 6, cause the backing off of the bolts automatically to back off or separate the endpieces from the frontpiece 4.

Identical with the first embodiment in the pivotal mounting of the pivoted member 1 and in the interlock between the upper and lower pieces 40 and frontpiece 41 of its frame 42 of the pivoted member, the pivoted member assembly of the second embodiment shown in FIGS. 11-15 differs from the first mainly in including as a subassembly, a rearview mirror assembly 43. Exemplary in its mirror assembly 43 of the mounting of a pivoted member within a frame or like boundary, the pivoted member l of this embodiment has its frame 42 closed at the rear by a vertically extending rear piece or part 44, overlapping and removably attached, as by bolting, to the rear ends of the upper and lower pieces 40. The space within the frame 42 is here divided into upper and lower openings 45 and 46, respectively, by a horizontally extending crosspiece, part or element 47, held in position on assembly of the frame, conveniently by supporting it on a U-shaped fillet 48 fitting in a groove 49 in the front, side and rear pieces of the frame 42 at the sides and bottom of the lower opening. One of the openings, here the upper opening 45, may be closed permanently by a glass or other transparent plate 50. The other or lower opening 44 contains the mirror 5l of the mirror assembly 43, the mirror preferably being of such size and so mounted on the crosspiece 48 as to be adapted substantially to close and to swing or pivot through the lower opening 46. For mounting it on the crosspiece 47, the mirror 5l here has a hinge lug 52 integral with and upstanding from its frame 53 and fitting into a downwardly opening recess 54 in and intermediate the ends ofthe crosspiece 47.

As does the mounting of the pivoted member l, that of the mirror 5l uses as its pivots 53 a pair of axially spaced, taper ended pivot pins, the tapered ends S6 of which fit into correspondingly tapered apertures or seats 57 in friction bushings S8 of brake lining or like suitable resilient material. Also, as in the main mounting, one ofthe pivot pins preferably is a double-ended pin 57 and the other a square or like out-of-round headed pivot pin 60. Of the several friction bushings 58, two are seated, socketed or received in opposite ends of the hinge lug 52 on the mirror frame 53 and the third is correspondingly mounted in a confronting end wall of the recess 54 in the crosspiece 47. The head 6l ofthe headed pivot pin 60 rides in and is held against rotation by a guide slot 62, conveniently formed in the other end wall of the recess 54 in the crosspiece 47 and the headed pin is shiftable to adjust the compression and consequent friction between the pivot pins S9 and 60 and the friction bushings 58 by an adjusting screw 63 which, by an cnd interfit with the head, also serves to maintain the headed pin in proper alignment.

lnsertable and accessible for adjustment through an aperture 64 in one of the front and rear pieces 4l and 43, here the rear piece, the adjusting screw 63 ofthe rearview mirror assembly 43 need not be locked against loosening due to vibration, since it is protected from vibration by the mounting of the pivoted member l. Preferably the frontpiece 4l of the frame 42 also is apertured in line with the pivotal axis of the mirror 49 so that, if desired, the mirror assembly 43, including the crosspiece 47, can be reversed for adjustment of the friction in the mounting from the front rather than the rear of the frame. With its pivotal axis preferably angularly related and, here, normal to that of the pivoted member l, the mirror 51 in effect is universally connected to the support for the main assembly and thus may be set at any desired angle.

From the above detailed description, it will be apparent that there has been provided an improved pivoted member assembly which is adjustable to hold a pivoted member by friction in any desired position and will maintain that adjustment regardless of outside forces. lt should be understood that the described and disclosed embodiments are merely exemplary of the invention and that all modifications are intended to be included that do not depart from the spirit of the invention or the scope of the appended claims.

Having described my invention, [claim:

l. A pivoted member assembly mountable on a support member, comprising a pivoted member, a frame at least partially bounding said pivoted member and including a sidepiece and an endpiece overlapping an end of and connectable to said sidepiece, bolt means inset and rotatable in said endpiece and threadedly engaging said sidepiece for releasably connecting said pieces, pivots pivotally connecting said pivoted and support members, each of said pivots including a rigid pivot pin and a tough resilient nonmetallic friction bushing having an aperture receiving an end of and separating said pin from one of said members, one of said bushings being releasably seated in said endpiece between said connecting bolt means and the associated pivot pin for releasably holding said bolt means against axial displacement relative to said piece while permitting access through its aperture of means for turning said bolt means.

2. A pivoted member assembly mountable on a support, comprising a pivoted member, a frame at least partially bounding said member and including a sidepiece and a pair of endpieces overlapping ends of and connectable to said side piece, pivots for pivotally mounting said pivoted member on said support, each of said pivots including an apertured tough resilient nonmetallic friction bushing; seated in one of said endpieces and a rigid pivot pin, each pin having an end received in and being spaced from its endpiece by one of said bushings, and a pair of bolts concentric with the pivot axis of said pivoted member and each connecting one of said endpieces to said sidepiece, said bolts threadedly engaging said sidepiece and being rotatable in said endpieces and inset therein inside said bushings, and said bushings engaging heads of and releasably holding said bolts against axial movement relative to said endpieces and through their apertures permitting access thereto of means for turning said bolts.

3. A pivoted member assembly comprising a pivoted member, a frame at least partially bounding said member and formed of a plurality of releasably connected pieces, bolts releasably connecting said pieces, a pair of mounting bracket members attachable to a support, a pair of pivots each pivotally connecting said pivoted member to one of said bracket members, each of said pivots including a rigid pivot pin having a tapered end and a tough resilient nonmetallic friction bushing apertured to receive said end and spacing said pin from and seating in one of said members connected by said pivot, certain of said bushings seating in said endpieces each outside of and engaging a head of one of said bolts for releasably holding said bolt against axial movement relative to the associated endpiece, an out-of-round slot in one of said bracket members nonrotatably receiving a correspondingly configured head of one of said pins, and an adjusting screw threaded into said one bracket in axial alignment with and having an end fitting into said head of said one pivot pin for adjusting the friction in said pivots while maintaining said one pin in alignment.

4. A pivoted member assembly comprising a pivoted member, a frame at least partially bounding said member and formed of a plurality of releasably connected pieces, bolts releasably connecting said pieces, a pair of mounting bracket members attachable to a support, a pair of pivots each pivotally connecting said pivoted member to one of said bracket members, each of said pivots including a rigid pivot pin having a tapered end and a tough resilient nonmetallic friction bushing apertured to receive said end and spacing said pin from and seating in one of said members connected by said pivot, certain of said bushings seating in said endpieces each outside of and engaging a head of one of said bolts for releasably holding said bolt against axial movement relative to the associated endpiece, an out-of-round slot in one of said bracket members nonrotatably receiving a correspondingly configured head of one of said pins, an adjusting screw threaded into said one bracket in axial alignment with and engaging said head of said one pivot pin for adjusting the friction in said pivots, and means for locking said adjusting screw in adjusted positionA 5. A pivoted member assembly comprising a pivoted member, a frame at least partially bounding said member and formed of a plurality of releasably connected pieces, bolts releasably connecting said pieces, a pair of mounting bracket members attachable to a support, a pair of pivots each pivotally connecting said pivoted member to one of said bracket members, each of said pivots including a rigid pivot pin having a tapered end and a tough resilient nonmetallic friction bushing receiving said end and spacing said pin from and seating in one of said members connected by said pivot, certain of said bushings being seated in said endpieces each outside of and engaging a head of one of said bolts for releasably holding said bolt against axial movement relative to the associated endpiece, an out-of-round slot in one of said bracket members nonrotatably receiving a correspondingly configured head of one of said pins, and an adjusting screw threaded into said one bracket in axial alignment with and engagin g said head of said one pivot pin for adjusting the friction in said pivots.

Claims

1. A pivoted member assembly mountable on a support member, comprising a pivoted member, a frame at least partially bounding said pivoted member and including a sidepiece and an endpiece overlapping an end of and connectable to said sidepiece, bolt means inset and rotatable in said endpiece and threadedly engaging said sidepiece for releasably connecting said pieces, pivots pivotally connecting said pivoted and support members, each of said pivots including a rigid pivot pin and a tough resilient nonmetallic friction bushing having an aperture receiving an end of and separating said pin from one of said members, one of said bushings being releasably seated in said endpiece between said connecting bolt means and the associated pivot pin for releasably holding said bolt means against axial displacement relative to said piece while permitting access through its aperture of means for turning said bolt means.

2. A pivoted member assembly mountable on a support, comprising a pivoted member, a frame at least partially bounding said member and including a sidepiece and a pair of endpieces overlapping ends of and connectable to said sidepiece, pivots for pivotally mounting said pivoted member on said support, each of said pivots including an apertured tough resilient nonmetallic friction bushing seated in one of said endpieces and a rigid pivot pin, each pin having an end received in and being spaced from its endpiece by one of said bushings, and a pair of bolts concentric with the pivot axis of said pivoted member and each connecting one of said endpieces to said sidepiece, said bolts threadedly engaging said sidepiece and being rotatable in said endpieces and inset therein inside said bushings, and said bushings engaging heads of and releasably holding said bolts against axial movement relative to said endpieces and through their apertures permitting access thereto of means for turning said bolts.

4. A pivoted member assembly comprising a pivoted member, a frame at least partially bounding said member and formed of a plurality of releasably connected pieces, bolts releasably connecting said pieces, a pair of moUnting bracket members attachable to a support, a pair of pivots each pivotally connecting said pivoted member to one of said bracket members, each of said pivots including a rigid pivot pin having a tapered end and a tough resilient nonmetallic friction bushing apertured to receive said end and spacing said pin from and seating in one of said members connected by said pivot, certain of said bushings seating in said endpieces each outside of and engaging a head of one of said bolts for releasably holding said bolt against axial movement relative to the associated endpiece, an out-of-round slot in one of said bracket members nonrotatably receiving a correspondingly configured head of one of said pins, an adjusting screw threaded into said one bracket in axial alignment with and engaging said head of said one pivot pin for adjusting the friction in said pivots, and means for locking said adjusting screw in adjusted position.

5. A pivoted member assembly comprising a pivoted member, a frame at least partially bounding said member and formed of a plurality of releasably connected pieces, bolts releasably connecting said pieces, a pair of mounting bracket members attachable to a support, a pair of pivots each pivotally connecting said pivoted member to one of said bracket members, each of said pivots including a rigid pivot pin having a tapered end and a tough resilient nonmetallic friction bushing receiving said end and spacing said pin from and seating in one of said members connected by said pivot, certain of said bushings being seated in said endpieces each outside of and engaging a head of one of said bolts for releasably holding said bolt against axial movement relative to the associated endpiece, an out-of-round slot in one of said bracket members nonrotatably receiving a correspondingly configured head of one of said pins, and an adjusting screw threaded into said one bracket in axial alignment with and engaging said head of said one pivot pin for adjusting the friction in said pivots.