US3620332A

US3620332A - Safety ladder

Info

Publication number: US3620332A
Application number: US762818*A
Authority: US
Inventors: Maurice A Bourquin
Original assignee: MAB Machine Corp
Current assignee: MAB Machine Corp
Priority date: 1970-08-11
Filing date: 1970-08-11
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16

Abstract

Attachments for the base portions of ladders which serve to laterally widen and forwardly extend the effective base of the ladder to give it stability on uneven or sloping supporting surfaces. Attachments are so designed as to transfer the major portion of the loading on the ladder to the attachments without placing shear stresses on the bolts or other devices securing the attachments to the rails of the ladder. Thus, repetitive use of the ladder will not cause the attaching devices to work loose since loading of such devices under tension rather than shear does not tend to cause progressive enlargement of the holes in the side rails through which such devices extend. Lower ends of side rails rest upon sloping shelves formed in the attachments while the front edge and one side surface of each rail is confined against rigid walls whereby loading of ladder tends to cause only a rocking of the attachments lengthwise of the attaching devices.

Description

United Mates atent [72] Inventor Maurice A. Bourquin East Granby, Conn.

[21] Appl. No. 62,818

[22] Filed Aug. 11, 1970 [45] Patented Nov. 16, 1971 [73] Assignee The M.A.B. Machine Corporation [54] SAFETY LADDER Primary E.taminer-Reinaldo P. Machado Attorney-James D. Bock ABSTRACT: Attachments for the base portions of ladders which serve to laterally widen and forwardly extend the effective base of the ladder to give it stability on uneven or sloping supporting surfaces. Attachments are so designed as to transfer the major portion of the loading on the ladder to the attachments without placing shear stresses on the bolts or other devices securing the attachments to the rails of the ladder. Thus, repetitive use of the ladder will not cause the attaching devices to work loose since loading of such devices under tension rather than shear does not tend to cause progressive enlargement of the holes in the side rails through which such devices extend. Lower ends of side rails rest upon sloping shelves formed in the attachments while the front edge and one side surface of each rail is confined against rigid walls whereby loading of ladder tends to cause only a rocking of the attachments lengthwise of the attaching devices.

PAIENTEUuuv 16 Ian SHEET 1 0F 2 Owl PATENTEDunv 18 M SHEET 2 [1F 2 SAFETY LADDER BACKGROUND OF THE INVENTION The prior art discloses many ladders constructed in such a manner or provided with attachments so as to afford a laterally and/or forwardly widened base for contact with the ground or other supporting surface. These are intended to give the ladder greater security upon uneven or sloping supporting surfaces and to permit the user to safely lean outwardly of the vertical center line of the ladder. Thus as shown in U.S. Pat. Nos. 843,989 and 1,134,491 lateral braces are swiveled or hinged to the side rails of ladders in such a manner as to afford additional footings therefor. In U.S. Pat. Nos. 808,124 and 2,354,904 lateral braces are rigidly attached to the side rails to afford a wider lateral base for the ladder. In U.S. Pat. Nos. 14,223 and 2,323,425 attachments are secured to the lower extremities of the side rails of ladders to widen the bases thereof. However, all of these patented structures, particularly when the ladder is used on uneven or sloping supporting surfaces, place great stress in shear upon the horizontally extending attaching devices such as bolts, screws and the like which extend through the side rails of the ladders. While it may be expected that such attaching devices will be so selected as not to fail in shear under such stresses a severe problem exists in that the attaching devices will work loose under repetitive loading as a result of enlarging of the holes due to local permanent compression of the wood through which the attaching devices extend. Such enlarging is progressive and cannot be completely compensated for by tightening of the fastening devices.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides attachments made of rigid material such as cast or fabricated sheet metal. The lower ends of the side rails of a ladder to which the attachments are to be adapted are cut off, as an incident to manufacture of a new ladder or deliberately in the event the attachments are to be adapted to an existing ladder. at a position just beneath the lowermost step. Such cutoff is made at an angle sloping downwardly and forwardly to match a downwardly and forwardly sloping shelf or pocket found in the attachments. The attachments are then secured to the side rails by bolts or the like extending through the attachments and the side rails in positions above the shelf or pocket. The attachments include outwardly flaring portions extending downwardly from the lowermost step of the ladder whereby to widen and forwardly extend the effective base of the ladder. Loads applied to the ladder are transferred to the shelves or pockets of the attachments and because of the flare ofthe lower portions of the attachments they will tend to rock about or pull away from the shelves or pockets. However, at least some of the bolts positioned above the shelves will react in tension to prevent such rocking and to confine the walls of the attachments tightly against the outer surfaces of the side rails. Thus relative movement between the attachments and the side rails is effectively prevented without placing sufficient stresses in shear upon the bolts to result in any progressive enlarging of the holes in the side rails through which the bolts extend.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a ladder embodying the present invention;

FIG. 2 is a side elevational view of the ladder shown in FIG.

FIG. 3 is a horizontal sectional view taken along the line 3- 3 in FIG. 2;

FIG. 4 is a generally vertical sectional view taken along the line 4-4 in FIG. 2;

FIG. 5 is a plan view of the attachment which is secured to the left-hand rail of the ladder shown in FIG. 1;

FIG. 6 is a front elevational view of said attachment;

FIG. 7 is a left-hand elevation of said attachment;

FIG. 8 is a right-hand side elevational view of said attachment;

FIG. 9 is a rear elevational view of said attachment; and

FIG. 10 is a sectional view similar to FIG. 4 but showing a modified form of the present invention. Referring now to the drawings:

An illustrative embodiment of the present invention is shown adapted to a conventional four-legged wooden step ladder. It will be understood that the present invention may be adapted to straight or extension ladders or to step ladders of the three-legged type. Also, it may be adapted to ladders of these various types made of other conventional materials such as steel or alloys of aluminum or magnesium whether the same be of tubular, solid or channel construction, as will be more fully explained hereinbelow. The conventional wooden step ladder 10 shown in Flg. 1 includes a left-hand side rail 12 and a right-hand side rail 14 between which are disposed the usual horizontal steps l6, 18, 20 and 22. Each of said steps may be provided, if so desired, with a reenforcing or tension rod 24 having a conventional screwhead at one end and a threaded portion at the opposite end to receive nuts 26.

At the top of the ladder 10 the

side rails

12 and 14 are secured to a conventional head or platform 28 the latter being thus secured, for example by metal brackets 30 and conventional screws or bolts 32.

Referring now to FIG. 2 the ladder 10 has hinged to the head 28 or to the brackets 30, as may be desired, a pair of rear legs 34 and 36 (see FIG. I). The

rear legs

34 and 36 are connected by conventional cross members 38 which may be reenforced by tension rods 40 similar to the rods 24 used in connection with the steps. The ladder 10 also may be provided with the conventional over-centering'toggle straps 42 which serve to hold the ladder in the position shown in FIGS. 1 and 2 and which may be swiveled upwardly to permit folding of the ladder. The ladder also may be provided with the conventional shelf 44 hinged at 46 to be swung into operational position as shown in FIG. 2 or into a folded position, in well-known manner.

In the conventional wooden step ladder the

side rails

12 and 14, the head 28 and the

rear legs

34 and 36 are made of wood as are the steps 16-22, rear spacing members 38 and the several parts of the shelf 44. The grain of the wood runs lengthwise of the

rails

12 and 14 and

rear legs

34 and 36. The present invention takes into account the fact that shrinkage of the wood in the rails I2 and 14 will occur primarily across the width thereof as viewed in FIG. 2, it being well known that wood shrinks very little lengthwise of the grain but frequently progressively shrinks across the grain during its normal service life.

While the present invention may be incorporated into an otherwise conventional wooden or other step ladder by the manufacturer thereof it is an important aspect of the present invention that it may be easily adapted to a conventional step ladder already owned by a user. To adapt an existing ladder to the present invention each of the side rails such as 12 and 14 in FIGS. 1 and 2 are sawed off along a plane 48 which is inclined downwardly from the rear edge of the rail toward the front edge thereof as shown in FIG. 2. In the form of the invention shown in FIGS. 2 and 4 the plane 48 is cut square with respect to the side surfaces of the rail as shown particularly in FIG. 4. In a modified version of the invention as shown in FIG. 10 a rail 214 of a conventional ladder is sawn along a plane 248 which is inclined as is the plane 48 but also is inclined downwardly from the outer side surface of rail 214 toward the inner side surface thereof for a purpose that will be explained hereinbelow.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The attachments embodying the present invention are indicated generally by the reference numerals 50 for the lefthand attachment and 52 for the right-hand attachment as viewed in FIG. 1. For purposes of illustration the

attachments

50 and 52 are shown as metal castings on which a minimum of machining operations are required. However, it will be apparent that they may be fabricated from several pieces of flat sheet metal welded or otherwise secured together or from metal sheets some of which have been bent into simple shapes so as to reduce the amount of welding or other fastenings required. In either event the attachments may be made from lightweight metal or metal alloys, if preferred, although when they are to be fabricated from sheet metal appropriate ferrous metals may be preferred because of low cost.

With particular reference to FIG. 4 which is a sectional view, looking towards the left in FIG. 2, of the attachment 52 it will be noted that the attachment 52 includes a check portion or plate 54 which is adapted to be secured against the outer surface of the side rail 14 of ladder l0. The cheek portion 54 rises from a relatively thick leg portion 56 having an upper surface 58 which constitutes a shelf upon which the lower surface 48 of the ladder side rail 14 is adapted to rest. The attachment 52, as shown in FIG. 4, also is provided with a generally vertically extending lip 60 (also see FIG. 3) which is adapted to fit firmly against the front surface of the side rail 14 as will be more clearly understood from the description below of the left-hand attachment 50 which is shown in full detail in FIGS. 5 through 9.

Preferably also, the attachment 52 includes a stiffening web 62 which extends from the upper end of cheek portion 54 to the lower end of leg portion 56 (see FIGS. 1 and 2 as well as FIG. 4).

Referring particularly to FIGS. 2 and 4 a simple and preferred manner of securing the attachment 52 to the righthand side rail 14 is shown. Thus the cheek portion 54 has drilled or otherwise formed therein a plurality of holes 64 to receive respectively a plurality of

bolts

66, 68, 70 and 72. Holes, not numbered, corresponding with the holes 64 are drilled through the side rail 14 in such position that, when the rail 14 is snugly fitted against the shelf 58 and lip 60, the

bolts

66, 68, 70 and 72 may be inserted through the rail 14 and each secured by a suitable nut 74. Washers of any suitable type (not shown) may be positioned beneath the bolt head or nuts if so desired.

Many ladders, including conventional wooden step ladders have the reenforcing or tension rods 24 shown for example, in

FIGS. 2 and 4, and described above. To afford clearance for and access to the screwheads of such rods and the nuts 26 threaded thereon a relatively large opening 76 may be formed in the cheek portion 54. In this manner the cheek portion 54 may extend above as well as below the level of the lowermost step l6 of the ladder thus affording wide spacing and good load distribution between the lowermost bolt 66 and the

uppermost bolts

70, 72 which secure the attachment S2 to rail I4.

in FIGS. through 9 the left-hand attachment 50 is shown in various plan and elevational views to afford solid line showing to the various portions thereof. The attachment 50 is a mirror image of the attachment 52 and parts thereof which have been described and identified by reference numerals in connection with the attachment 52 will be only briefly described and will be identified by the same reference numerals plus the digit 1 in the hundreds place. In all of these Figures the cheek portion I54 of attachment 50 is shown in a vertical position rather than in the two-dimensional slantwise position which it assumes when attached to a step ladder having rails which converge toward the top. In other words the attachment 50 is shown in the position it would assume if the ladder 10, in FIG. 1, were to be tilted towards the left to bring the left-hand rail 12 into a vertical position parallel, for exampIe with the broken line 78 in FIG. I.

Thus, in FIG. 5 a portion of the upper surface of the shelf I58 upon which the sawn-off lower end 48 of the rail 12 rests, is shown in full lines. In FIG. 6 the front surfaces are shown in full lines as in FIG. I but in such scale that the thickness of leg portion 156 may be shown by dotted as well as full lines. Also, the relationship of the cheek portion 154 with the leg portion 156 and web portion I62 as these portions merge beneath the shelf 158 is shown by dotted lines since such portions are concealed by the web 162 in the position illustrated in FIG. 6.

In FIG. 7, which is a mirror image of FIG. 2 the scale permits the showing by dotted lines of the manner in which the lower end 148 of the rail 12 rests within the pocket afforded by the cheek portion I54, shelf 158 and the lip 160. In FIG. 8 the pocket just mentioned is shown in full lines. In FIG. 9 a substantial portion of the inner surface of lip 160 is shown in full lines.

The modification shown in FIG. 10 involves only the fact that the upper surface of the shelf 258 is slanted downwardly and inwardly from the outer, or right hand, surface of the attachment 252 as viewed in said FIG. 10. As noted above for use with an attachment as shown in this FIG. I0, the lower end of the rail 214 of the ladder with which the attachment is to be used is cut or sawn oh at a compound angle such as to fit snugly upon the inwardly inclined portion of the shelf 258 as well as to fit the forward and downward decline thereof in accordance with the showing in FIGS. 2 and 8.

From a consideration of FIGS. 1, 2 and 4 the reasons for the substantial immunity of any of the attachments disclosed herein against working loose and thus becoming unsafe or at least creating an impression of unsafeness, will become understood. As viewed in FIG. I the

attachments

50 and 52 are splayed laterally to provide, in effect, a broader transverse base for the ladder 10. Whether the side rails I2 and I4 themselves are somewhat splayed as is shown in FIG. I and as is customary with step ladders at least, or the side rails were parallel as is sometimes the case, the splaying of the

attachments

50 and 52 causes any vertical loading upon the ladder to tend to spread the lower ends of the attachments further apart. This effect is resisted by the relative rigidity of the side rails 12 and 14 of the attachments. However these relatively rigid parts must be connected in such manner as not to concentrate forces at points where crushing of wood parts or distortion of metal parts will cause loosening of the connections between the rails and the attachments.

The manner of connecting the

attachments

50 and 52 to the

rails

12 and 14 meets these requirements in a simple and effective manner since the lower cutofi ends 48 of the rails rest upon the shelves (see shelf 58 in FIG. 4 for example) and the outer sides of the

rails

12 and 14 are tightly secured against the cheek portions (see cheek portion 54 in FIG. 4). Thus a load which tends to rock the leg 56 (FIG. 4) leftwardly from beneath the end 48 of rail 14 is transferred by the cheek portion 54 to the

bolts

66, 68, 70 and 72 which react in tension and, in turn, transfer the load to the inner surface of rail 14 through the nuts 74. So long as the lower end 48 of rail 14 rests on shelf 58 there is substantially no shear loading placed upon the bolts 66-72 and progressive enlargement of the holes through which the bolts extend in rail 14 will not occur.

While the rail 14 may be expected to shrink, assuming that it is made of wood, such shrinkage is confined almost entirely to the cross grain directions, that is the width and thickness of the rail. Shrinkage in thickness of rail 14 as viewed in FIG. 4 may result in slight loosening of the bolts and this will permit the lower end 48 to settle upon the shelf 58 in the event any lengthwise shrinkage of the wood has occurred. Occasional retightening of nuts 74 will fully compensate for shrinkage even if the rails had been made of poorly seasoned wood. Thus it is assumed that the lower ends 48 will continue to firmly rest upon shelf 58 and the pattern of load distribution will not change under repeated loading and unloading of the ladder.

As viewed in FIG. 2 the

attachments

50 and 52 also extend the base of ladder l0 forwardly and vertical loading on the ladder will tend to rock the attachments in a clockwise direction as viewed in that Figure. This tendency is resisted by the pressure of lip 60 against the front of rail 14, for example, and the pressure of the lower end 14 thereof against the downwardly and forwardly inclined surface of shelf 58. The extensive length of the lip 60 and the wedging action between the end 48 and shelf 58 affords large bearing areas with little likelihood of concentration of stresses on local points. The fastening devices such as bolts 66-72 play little. if any, part in the transfer of loading between rail 14 and the attachment 52. Shrinkage in width and thickness of a wooden rail 14 may lead to slight loosening of the bolts 6672 as noted above, and may tend to cause some retraction of the front of rail 14 away from lip 60. However, this is self-compensating since the rail 14 will settle by sliding of the end 14 downwardly upon shelf 58 and occasional retightening of the nuts 74 is all that may be required to restore desired rigidity to the structure.

if so desired the holes 64 in the cheek portion 54 (see FIG. 4) which receive the bolts 66-72 may be made somewhat larger in diameter than the diameter of the bolts to permit initial adjustment and such readjustment as possibly may be required after shrinkage of the

rails

12 and 14 when the latter are made of wood.

The

attachments

50 and 52 are so constructed that they may be applied to ladders having rails of any width or thickness. Thus, the pocket made up of the upper surface 58 (or 158 in FIG. 8), the inner surface of lip 60 (or lip 160 in Fig. 8) and the inner surface of cheek portion 54 (or lip 154 in H0. 8) is open on three sides so that rails of greater or lesser width or thickness than the rails illustrated in the drawings can be readily accommodated. This is also true in the modified form of attachment shown at 252 in FIG. [0.

In the modification shown in FIG. the downwardly and outwardly inclined lower end 248 of rail 214 bears against the correspondingly inclined surface 258 of the attachment. In this modification even greater resistance is afforded against lateral spreading of the attachments under load because of the wedging ofthe end 248 against the surface 258.

It is intended that the attachments of the present invention may be sold to ladder manufacturers or to individuals owning an existing ladder. For the latter type of purchaser the attachments with required nuts and bolts may be sold in kit form. ln that case it may be desirable to supply with the kits suitable templates, such as printed paper sheets, with pressure-sensitive adhesive if so desired, so that the angle and position of the line along which the rails are to be cut may be readily and accurately determined. Also, such templates may have the centers and diameters of the holes to be drilled accurately located and indicated.

The adaptability of this invention to metal ladders, step or straight, will be apparent. The side rails of metal ladders may be tubular, channel shaped or of special shaped but in any event the lower portions thereof are cut at an angle to match the angles of the shelves 58 of the attachments. The check plate portions 54 may lie against a flat metal exterior surface of such metal side rails or may bear only upon the edges of flanges or other shapes which define the outer surfaces of the side rails.

ln the claims the word steps" is intended to include the flat steps used in step ladders as well as the steps sometimes called rungs in a straight ladder.

The fastening devices are shown herein as conventional bolts 66-72 and nuts 74 and it will be understood that any sort of tension fasteners may be used instead. For example rivets or so-called sheet metal screws or sheet metal bolt substitutes may be used.

What is claimed is:

l. A pair of attachments for enlarging the effective base of a ladder having two side rails and a plurality of steps secured to and extending between said side rails, said ladder when positioned for normal use having each of said side rails generally vertically disposed and each presenting to the user front, rear, outside and inside surfaces and having said steps extending generally horizontally, and each of said side rails terminating below the lowermost of said steps in a downwardly and forwardly inclined lower surface. each of said attachments being adapted to be attached to a side rail of said ladder and each having a leg portion which is splayed laterally outwardly with respect to the side rail to which it is to be attached, each of said attachments having a supporting shelf downwardly and forwardly inclined to match the downward and forward incline of the lower surface of the side rail to which it is to be attached and upon which shelf said lower surface of said side rail is adapted to rest, each of said attachments having a cheek plate extending upwardly from said shelf and adapted to engage in face-to-face relation against the outside surface of the side rail to which it is to be attached, each of said attachments having a lip extending substantially at right angles with respect to said cheek plate and extending upwardly from said shelf in such position as to engage in face-to-face relation with the front surface of the side rail to which it is to be attached and fastening means of the tension type for securing each of said attachments to the side rail to which it is to be attached with each of said cheek plates in said face-to-face relation with said side rail, with said lower surface of said side rail resting upon said shelf and with said front surface of said side rail in said face-to-face relation with said lip.

2. A pair of attachments in accordance with claim 1 in which the leg portion of each of said attachments also splayed forwardly with respect to the side rail to which said attachment is to be attached.

3. A pair of attachments in accordance with claim 1 in which each of said attachments has the cheek plate and the lip thereof extending upwardly from the shelf thereof for a distance sufficient to extend above the lowermost step of the ladder to which said attachments are to be attached.

4. A pair of attachments in accordance with claim 1 in which the shelf of each of said attachments is also inclined inwardly and downwardly with respect to the side rail to which said attachment is to be attached thus adapting each of said attachments to be attached to a side rail having the lower surface thereof also inclined inwardly and downwardly.

5. In a ladder having two side rails and a plurality of steps secured to and extending between said side rails, said ladder when positioned for normal use having each of said side rails generally vertically disposed and each presenting to the user front, rear outside and inside surfaces having said steps extending generally horizontally, each of said rails terminating below the lowermost of said steps in a downwardly and forwardly inclined lower surface, the improvement which comprises an attachment for each of said side rails each of said attachments having a leg portion which is splayed laterally outwardly with respect to the side rail with which it is associated, each of said attachments having a supporting shelf downwardly and forwardly inclined to match the downward and forward incline of the lower surface of the associated side rail and upon which shelf said lower surface is adapted to rest, each of said attachments having a cheek plate extending upwardly from said shelf and adapted to engage in face-to-face relation against the outside surface of the associated side rail, each of said attachments having a lip extending substantially at right angles with respect to said cheek plate and extending upwardly from said shelf in such position as to engage in face to-face relation with the front surface of the associated side rail, and fastening means of the tension type for securing each of said attachments to its associated side rail with each of said cheek plates in said face-to-face relation with the associated side rail, with said lower surface of the associated side rail resting upon said shelf and with said front surface of the associated side rail engaged with said lip.

6. A ladder in accordance with claim 5 in which said leg portion of each of said attachments is also splayed forwardly with respect to said side rail.

7. A ladder in accordance with claim 5 in which said cheek plate and said lip of each of said attachments extends upwardly of said side rail for a substantial distance above said lowermost step.

8. A ladder in accordance with claim 5 in which said lower surface of each of said side rails is also inclined inwardly and downwardly, and in which said shelf of each of said attachments is also inclined inwardly and downwardly to match the inward and downward incline of the lower surface of the associated side rail.

UNITED 5? TBS PATENE? *i FicE fiER'iJQFICATE fifiRREQTMN Patent No 3,620,332 f t d November'- 16, 1971 J! Inventdfls) Maun ce A. Bourqudkn It is certified that error appears in the above-identifiefi patent and that said Letters Patent are hereby correcteci as shown below:

decline shculd be --inc1ine- Col. 4, line 16 col. 4, line 31 before "of" insert -and-- Col. 5, line 42 "shaped" should be --shapes- E '1 *1. MQ ...:a ii II mm CO1 .une amoraat .Llxmci v on-- Col. 6 ine 35 before "having" insert --anc'i-- Claim 5 5F sealed this 23rd day of May 3972.

smL)

FL, FL 3'51 & HO r GOTT so s-Lzzeauiag Sfficer Commissioner 0'1" Patents

Claims

1. A pair of attachments for enlarging the effective base of a ladder having two side rails and a plurality of steps secured to and extending between said side rails, said ladder when positioned for normal use having each of said side rails generally vertically disposed and each presenting to the user front, rear, outside and inside surfaces and having said steps extending generally horizontally, and each of said side rails terminating below the lowermost of said steps in a downwardly and forwardly inclined lower surface, each of said attachments being adapted to be attached to a side rail of said ladder and each having a leg portion which is splayed laterally outwardly with respect to the side rail to which it is to be attached, each of said attachments having a supporting shelf downwardly and forwardly inclined to match the downward and forward incline of the lower surface of the side rail to which it is to be attached and upon which shelf said lower surface of said side rail is adapted to rest, each of said attachments having a cheek plate extending upwardly from said shelf and adapted to engage in faceto-face relation against the outside surface of the side rail to which it is to be attached, each of said attachments having a lip extending substantially at right angles with respect to said cheek plate and extending upwardly from said shelf in such position as to engage in face-to-face relation with the front surface of the side rail to which it is to be attached and fastening means of the tension type for securing each of said attachments to the side rail to which it is to be attached with each of said cheek plates in said face-to-face relation with said side rail, with said lower surface of said side rail resting upon said shelf and with said front surface of said side rail in said face-to-face relation with said lip.

5. In a ladder having two side rails and a plurality of steps secured to and extending between said side rails, said ladder when positioned for normal use having each of said side rails generally vertically disposed and each presenting to the user front, rear outside and inside surfaces having said steps extending generally horizontally, each of said rails terminating below the lowermost of said steps in a downwardly and forwardly inclined lower surface, the improvement which comprises an attachment for each of said side rails each of said attachments having a leg portion which is splayed laterally outwardly with respect to the side rail with which it is associated, each of said attachments having a supporting shelf downwardly and forwardly inclined to match the downward and forward incline of the lower surface of the associated side rail and upon which shelf said lower surface is adapted to rest, each of said attachments having a cheek plate extending upwardly from said shelf and adapted to engage in face-to-face relation against the outside surface of the associated side rail, each of said attachments having a lip extending substantially at right angles with respect to said cheek plate and extending upwardly from said shelf in such position as to engage in face-to-face relation with the front surface of the associated side rail, and fastening means of the tension type for securing each of said attachments to its associated side rail with each of said cheek plates in said face-to-face relation with the associated side rail, with said lower surface of the associated side rail resting upon said shelf and with said front surface of the associated side rail engaged with said lip.