US3734237A - Ladder - Google Patents

Abstract

Disclosed is a strong, lightweight, electrically nonconductive ladder having two slotted wood side rails spanned by tubular metal rungs. Each rail comprises two parallel wood slats oriented perpendicular to the plane of the ladder and spaced apart in the plane to the ladder by spaced, thin, rectangular wood chocks adhesively bonded in face to face relation to the slats. Tensioned tie rods extending through the rungs compressively hold the rungs socketed anti-rotationally in and between the side rails in an integral structure resistant to racking, bending or torsional strain.

Description

United States Patent [191 Howard [1 1 3,734,237 1 May 22,1973

[ LADDER [75] Inventor: Charles I. Howard, Mercer Island,

Wash.

[73] Assignee: Howard Manufacturing Company,

Kent, Wash.

[22] Filed: Mar. 16, 1971 [21] Appl. No.2 124,773

[52] US. Cl ..182/2l6, 182/219 [51] Int. Cl. ..E06c 1/08, E06c 7/08 [58] Field of Search ..182/194, 219, 216, 182/215 [56] References Cited UNITED STATES PATENTS 322,980 7/1885 Schumman ..1'82/219 2,739,847 3/1956 Webb ....182/119 3,369,630 2/1968 Rich ..182/2l6 FOREIGN PATENTS OR APPLICATIONS 1,120,034 7/ 1968 Great Britain ..l82/228 Primary ExaminerReinaldo P. Machado Attorney--Christensen & Sanborn [5 7 ABSTRACT Disclosed is a strong, lightweight, electrically nonconductive ladder having two slotted wood side rails spanned by tubular metal rungs. Each rail comprises two parallel wood slats oriented perpendicular to the plane of the ladder and spaced apart in the plane to the ladder by spaced, thin, rectangular wood chocks adhesively bonded in face to face relation to the slats. Tensioned tie rods extending through the rungs compressively hold the rungs socketed anti-rotationally in and between the side rails in an integral structure resistant to racking, bending or torsional strain.

11 Claims, 6 Drawing Figures Patented May 22, 1973 flTTOENEKS LADDER BACKGROUND OF THE INVENTION This invention relates to a ladder and more particularly to a lightweight ladder having slotted side rails. Ladders having trussed or skeleton-type side rails built up from wood and/or metal members of various sizes and shapes are known in the art. Exemplary of such ladders are those disclosed in U.S. Pat. Nos. 886,514, 916,602, 1,491,648, 1,653,248 and 2,153,127. The ladder of this invention has slotted side rails each of which is comprised of a plurality of wood slats and chocks formed, assembled and interconnected with rungs and tie rods in a unique manner.

SUMMARY OF THE INVENTION The ladder of this invention has a pair of side rails spanned by and secured to a plurality of spaced apart rungs. Each of the rails comprises a pair of longitudinally extending wood slats having faces oriented generally perpendicular to the plane of the ladder and being spaced apart in the plane of the ladder by a plurality of chocks secured therebetween in face to face relation with each of the slats. The chocks are mutually spaced apart lengthwise of the rail, and selected chocks are positioned proximate the ends of rungs. Preferably, the chocks are separate pieces of wood with faces adhesively bonded to the faces of the respective slats.

A preferred embodiment of the ladder of this invention comprises a pair of parallel side rails, a plurality of parallel, uniformly spaced-apart tubular metal rungs spanning the rails and connecting means for maintaining the rails and rungs in assembled relation. Each rail comprises a pair of wood slats extending substantially the length thereof and having mutually parallel opposing faces oriented generally perpendicular to the plane of the ladder. The opposing faces of the pair of slats are spaced apart in the plane of the ladder by first and second sets of wood chocks adhesively bonded therebetween in face to face relation therewith. Chocks of the first set have face dimensions substantially greater than the diameter of the rungs and are spaced apart lengthwise of the rail generally coincident with the longitudinal axes of the rungs. Chocks of the second set are spaced intermediate those of the first, such that slots are provided along the length of the rail. The rung ends are anti-rotationally fitted in socket openings in the rails, each opening and rung end extending through one slat of a rail and partially through a chock of the first set. Each of the connecting means comprises a metal tie rod extending axially through a rung and through both rails and means cooperating with the ends of the rod for placing the ladder parts under compression along the axis of the rung, whereby the rails and rungs are maintained in assembled relation.

It is an object of this invention to provide a lightweight ladder which is strong and resistant to racking, twisting and bending loads, a ladder which for its length and weight is stiff. Another object of this invention is to provide a lightweight ladder which is nonconductive of electricity along its length. A further object is to provide a ladder having wood side rails which are resistant to warping and other effects of weathering. It is also an object of this invention to provide a ladder having a unique rail design wherein a plurality of wood members are bonded together with an adhesive. Still another object of this invention is to provide an improved ladder making improved combined use of wood and metal, including a novel juncture between the dissimilar materials so as to achieve not only the improved functional characteristics but cost reduction in original manufacture and subsequent repairs. Yet another object is to provide a lightweight ladder which can be conveniently disassembled for repair. Further objects and advantages of this invention will become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a front elevation view of a segment of a ladder constructed according to this invention.

FIG. 2 is an enlarged section view along line 2-2 of FIG. 1.

FIG. 3 is an enlarged view of the juncture of a rail and rung of the ladder of FIG. 1.

FIG. 4 is an exploded isometric view of the rail-rung juncture of FIG. 3.

FIGS. 5 and 6 are side and end views, respectively, of a rung end and depict the manner in which it can be formed using a double-bladed saw.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIGS. 1 through 4, a ladder according to this invention comprises two slotted side rails 1 spanned by a plurality of tubular, longitudinally ribbed, aluminum rungs 2. Each rail has a pair of wood slats 3 oriented with their faces perpendicular to the plane of the ladder and spaced apart in the plane of the ladder by three sets of small rectangular wood chocks 4, 4a and 4b oriented in face to face relation with the slats. (As used herein and in the appended claims a slat is a wood member which is thin and narrow in comparison to its width and length, respectively; a face is a surface defined by the length and width of a structural member; and an edge is a surface defined by the length and thickness or width and thickness of a structural member.) The chocks are spaced apart lengthwise of the rail such that slots 5 remain between the slats. Chocks of the first set 4 are positioned coincident with the longitudinal axes of the rungs, those of the second set 4a are positioned halfway therebetween and those of the third set 4b are positioned at the extreme ends of the rails. The slats and chocks are made from different lengths of the same wood stock, five-sixteenths by two-three-fourths inch kiln dried hemlock being preferred. In the ladder shown in the drawings, the dimensions of the chocks of the first and third sets 4 and 4b measured along the rail is two inches and that of the second set 4a is one-one-fourth inches. The slots between chocks of the first and second sets are four-- three-eighths inches long. Preferably, the combined lengths of the slots represent from about one-third to three-fourths of the length of the rail.

The slats and chocks are positioned such that their edges extending lengthwise of the rail are coplanar. This coplanar positioning of the edges of the slats and chocks maximizes the edge strength of the rail. As shown in FIG. 4, the slats and chocks are secured together with a hard-setting, moisture resistant, structural adhesive or glue 13 applied to both faces of the chocks and the inner faces of the slats. A preferred adhesive for this purpose is a resorcinol glue RS216 available from Borden Chemical Company. Longitudinally extending grooves 14 in the outer face of each slat improve the warp resistant characteristics of the rail.

Referring in particular to FIGS. 2 through 4, each rung end is inserted into a snugly-mating socket hole 6 in one of the rails. The socket hole extends through the inside slat of the rail and about one-eighth inch into a chock of the first set 4. A tooth 7, which projects longitudinally from one end of the rung, bites into the wood of the chock 4 at the end of the socket hole 6 and thereby prevents rotation of the rung during use of the ladder. Referring to FIGS. and 6, this tooth 7 can be formed by using a double-bladed circular saw A in which one blade is slightly smaller in diameter than the other. When the saw is used to cut off the rungs from lengths of tubing stock, the cutting stroke is terminated before the smaller blade passes through the stock so as to leave the arcuate tooth 7.

The rungs and rails are secured together by metal bolts or tie rods 8 extending axially through the rungs and through small holes (FIG. 4) in each rail, the small holes being coaxial with the larger socket holes into which the rung ends are inserted. Circular washers 9 are fitted on each end of the bolt, one washer being engaged by the bolt head 10 and the other by a nut 11 threaded on the end of the bolt. When the nut is drawn down tightly, the rails are compressed by the washers against the rung ends to form a unified ladder structure which is lightweight and yet exceptionally strong and rigid. Diagonal braces 12 (FIG. 1) located at intervals along the ladder, add to its overall strength and rigidity.

Numerous advantages flow from the overall design, and especially the rail design, of the ladder of this invention. For example, when compared to most commercial ladders having aluminum, fiberglass or solid wood side rails, for its weight and length the ladder of this invention is more rigid and thus less susceptible to bending and swaying during use and is more economical to manufacture from a standpoint of both material and labor costs. With specific reference to the rails of the ladder of this invention, their design is such that the rail components can be manufactured from economical sizes and grades of lumber and can be secured together with economical adhesives rather than mechanical connectors. The use of adhesives is especially advantageous because the exceptionally strong joints and rigid rail structure that result. The open design of the rail promotes even drying of the wood, when partially green or subsequently exposed to weathering, and thus minimizes warping due to differential moisture absorption and drying. Moreover, in case of part damage, economic repair is readily possible by removing the tie rods in order to disassemble the ladder.

I claim:

l. A ladder comprising a pair of generally parallel, slotted side rails spanned by and secured to a plurality of spaced-apart tubular metal rungs, each rail comprising a pair of wood slats extending the length of the rail, the faces of the slats being generally perpendicular to the plane of the ladder and being spaced apart in the plane of the ladder by first and second sets of wood chocks sandwiched therebetween and adhesively bonded thereto in face-to-face relation, chocks of the first set being mutually spaced apart lengthwise of the rail and being positioned generally coincident with the longitudinal axes of the rungs and chocks of the second set being mutually spaced apart and positioned intermediate those of the first set, selected chocks being so spaced apart from immediately adjacent chocks that the rail includes a plurality of slots extending therethrough between its longitudinal edges, the ends of said rungs being inserted in snugly mating sockets in the rails, each socket and rung end extending through one slat and only partially through a chock of the first set; and said ladder further comprising a plurality of metal rods, each passing axially through a rung and through both of the rails and means cooperating with the ends of the rods for engaging the outer faces of the rails and placing the ladder under compression along the longitudinal axes of the rungs, whereby the rails and rungs are maintained in assembled relation.

2. The ladder of claim 1 wherein the combined dimensions of the slots measured along the rail equal from one-third to three-fourths the length of the rail.

3. The ladder of claim 1 wherein the slats and chocks are of about the same thicknesses.

4. The ladder of claim 1 wherein the slats and chocks in a rail are dimensioned and positioned such that the edges thereof extending longitudinally of the rail are substantially coplanar.

5. The ladder of claim 4 wherein the combined dimensions of the slots measured along the rail equal to one-third to three-fourths of the length of the rail.

6. The ladder of claim 4 wherein the slats and chocks are of about the same thicknesses.

7. A ladder comprising a pair of parallel side rails, a plurality of parallel, uniformly spaced-apart tubular metal rungs spanning the rails, and connecting means for maintaining the rails and rungs in assembled relation; wherein each rail comprises a pair of wood slats extending substantially the length of the rail and having opposing faces oriented perpendicular to the plane of the ladder and spaced apart in the plane of the ladder by first and second sets of wood chocks sandwiched therebetween and secured thereto in face to face relation, the chocks of the first set being mutually spaced apart lengthwise of the rail, having face dimensions substantially greater than the diameter of the rungs, and being positioned coincident with the longitudinal axes of the rungs, and the chocks of the second set being spaced apart from chocks of the first set; wherein the ends of the rungs are inserted in snugly mating sockets in the rails, each socket and rung end extending through one slat and partially through a chock of the first set; and wherein each of the connecting means comprises a metal rod extending axially through a rung and means cooperating with the ends of the rod for placing the ladder under compression along the longitudinal axis of the rung whereby the rails and rungs are maintained in assembled relation.

8. The ladder of claim 7 wherein the slats and chocks are bonded together by an adhesive.

9. The ladder of claim 7 wherein the slats and chocks are dimensioned and positioned such that the edges thereof extending longitudinally of the rail are substantially coplanar.

10. The ladder of claim 9 wherein the slats and chocks are bonded together by an adhesive.

11. The ladder of claim 10 wherein the chocks are uniformly spaced apart lengthwise of the rail and wherein the dimensions of the chocks measured lengthwise of the rail are smaller than the distance by which adjacent chocks are spaced apart.

Claims (11)

1. A ladder comprising a pair of generally parallel, slotted side rails spanned by and secured to a plurality of spaced-apart tubular metal rungs, each rail comprising a pair of wood slats extending the length of the rail, the faces of the slats being generally perpendicular to the plane of the ladder and being spaced apart in the plane of the ladder by first and second sets of wood chocks sandwiched therebetween and adhesively bonded thereto in face-to-face relation, chocks of the first set being mutually spaced apart lengthwise of the rail and being positioned generally coincident with the longitudinal axes of the rungs and chocks of the second set being mutually spaced apart and positioned intermediate those of the first set, selected chocks being so spaced apart from immediately adjacent chocks that the rail includes a plurality of slots extending therethrough between its longitudinal edges, the ends of said rungs being inserted in snugly mating sockets in the rails, each socket and rung end extending through one slat and only partially through a chock of the first set; and said ladder further comprising a plurality of metal rods, each passing axially through a rung and through both of the rails and means cooperating with the ends of the rods for engaging the outer faces of the rails and placing the ladder under compression alOng the longitudinal axes of the rungs, whereby the rails and rungs are maintained in assembled relation.

2. The ladder of claim 1 wherein the combined dimensions of the slots measured along the rail equal from one-third to three-fourths the length of the rail.

3. The ladder of claim 1 wherein the slats and chocks are of about the same thicknesses.

4. The ladder of claim 1 wherein the slats and chocks in a rail are dimensioned and positioned such that the edges thereof extending longitudinally of the rail are substantially coplanar.

5. The ladder of claim 4 wherein the combined dimensions of the slots measured along the rail equal to one-third to three-fourths of the length of the rail.

6. The ladder of claim 4 wherein the slats and chocks are of about the same thicknesses.

7. A ladder comprising a pair of parallel side rails, a plurality of parallel, uniformly spaced-apart tubular metal rungs spanning the rails, and connecting means for maintaining the rails and rungs in assembled relation; wherein each rail comprises a pair of wood slats extending substantially the length of the rail and having opposing faces oriented perpendicular to the plane of the ladder and spaced apart in the plane of the ladder by first and second sets of wood chocks sandwiched therebetween and secured thereto in face to face relation, the chocks of the first set being mutually spaced apart lengthwise of the rail, having face dimensions substantially greater than the diameter of the rungs, and being positioned coincident with the longitudinal axes of the rungs, and the chocks of the second set being spaced apart from chocks of the first set; wherein the ends of the rungs are inserted in snugly mating sockets in the rails, each socket and rung end extending through one slat and partially through a chock of the first set; and wherein each of the connecting means comprises a metal rod extending axially through a rung and means cooperating with the ends of the rod for placing the ladder under compression along the longitudinal axis of the rung whereby the rails and rungs are maintained in assembled relation.

8. The ladder of claim 7 wherein the slats and chocks are bonded together by an adhesive.

9. The ladder of claim 7 wherein the slats and chocks are dimensioned and positioned such that the edges thereof extending longitudinally of the rail are substantially coplanar.

10. The ladder of claim 9 wherein the slats and chocks are bonded together by an adhesive.

11. The ladder of claim 10 wherein the chocks are uniformly spaced apart lengthwise of the rail and wherein the dimensions of the chocks measured lengthwise of the rail are smaller than the distance by which adjacent chocks are spaced apart.

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