US2511077A

US2511077A - Ladder

Info

Publication number: US2511077A
Application number: US56223A
Authority: US
Inventors: Jr Austin T Race
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-10-23
Filing date: 1948-10-23
Publication date: 1950-06-13
Anticipated expiration: 1967-06-13

Description

A. T. RACE, JR

June 13, 1950 LADDER Filed 001;. 25, 1948 me/wm Ausf/N 7.' RAC@ di?.

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Patented June 13, 1950 UNITED STATES QFFICE ,2,511,677l LADDER Austin T. Race., Jr., Winter Haven, sie.

Application October 23, 1948, Serial No@ 56,223

Claims.

This invention relates to improvements in ladders and particularly to a novel and improved means of attaching the rungs to the side rails.

In the manufacture of ladders, diiioulty has heretofore been experienced in the securing of the ends of the rungs to the side rails. Itis the rigidity of the connection between the run-gs and the side rails which gives strength and rigidity to the ladder. It will be appreciated that because the ends of the siderails cannot always be placed on a rigid level surface when a personclimbs upon the rungs of the ladder excessive stress is placed on the connections between the rungs and thel side rails because of the relativelongitudinal displacement which accompanies the excessive stress. Also in view of the fact that it often happens that the two ends of the side rails are not in a common plane, the ladder will also be subjected to a certain amount of twist. This is particularly true in orchard ladders where the upper end of the ladder is placed against the mass of limbs and branches to prevent injury tothe tree. In addition to the stresses andstrains mentioned above, the rungs are always subjected to a certain amount ofturning moment when they are in suc-h a stressed condition, Al-lor"- this tends to loosen the ordinary connection between the rungs and the side rails.

Heretofore numerous meanshave` been used in an attempt to overcome this diiculty. In wooden ladders attempts have been made to provide a wedging t betweenthe rungs and thesiderai-ls, insomel instances the wooden rungs being provided with metal ferru-les through which therung is attached to the side rails. common to have bolts engaging both siderails and pulling the side rails togetherv against the ends lof the rung. Duey to the susceptibilityofthe wood to swell when wet and to shrink when dry, it is practically impossible to maintain the rungsin such tight relation with the side rails as to maintain a rigid ladder. Heretofore when metal rungs have been employed the problem of securingv the ends of the rungshasbeen ver-y difficult andweldinghas been resorted to in certain` instances. However, due to the excessivelocalized: stresses which are developed in the connection between the rungs and the side rails, this method besides being expensive, is very unsatisfactory. Also, previous attempts have been made to rivetA the rungs to the side rail elements but here again this method is unsatisfactory from thestandpoint of cost as well as from the standpoint ofV failing to provide a rigid connection which will remainrig-id throughout the life of theladder.

Also, it has been Accordingly-the primary object of the present' invention iste provide an improved means for anchoring the ends ofthe rungs tothe side rails or to elementsfwhich can be rigidly attached to: the side rails.

Other and further objects wil-l become readily apparent from the following description when considered inconneotion with the accompanying drawings, illustrating an embodiment of the invention, and in which:

' Fig-ure 1 is ,a partialside view, partially-insection, of the lladderembodying the present invention;

Figure 2 is a profile view of Figure 1;

Figure 3= is a sectional view through one of the rungs and the side rails; and

Figure 4 is a sectional view on line -ll of Fig,- ure 3- looking in thel direction ofthe arrows'.V

The ladder shown for theY purpose of illustrating anembod-iment of the invention comprises side rail assemblies I` and"2 and' a plurality of rungs- 3. The side rail assemblies-shown are preferably made or" elongated member-s off' lf-section which arev held in spaced relation by rung-holder spacers' 6; Thrung holders are spaced longi-tirdinally of thev side rail assembliesA` the desired distance between the steps of the ladder. In the embodiment illustrated the partsI areO all made of aluminum alloy, the relative hardness-ofwhich is related to the inventive concept.

It has been found that the only practical way to form a rig-id connection betweenthe rungs 3 and the rung holders 6 is to assemble the elements in such aman-ner that in the final assembly the metai o1"v4 the rung w-ilr be under very highcompressivef stresses. 'In order' to insure that these high compressive stresses will be maintained un der all= conditions under whichi the-1 ladder isA used, thereby" preventingf looseness"r from developingin the connection, is to provide an expanded-v section associated with the'l section wlfiifch is under high compressive stresses. To thisendthe' present-in'- ventioncontemplates the' utilization" or alloys in ther-ungs- 3V and'in the rung holders or different relative hard-nessso that the' corrugationslonfone oi the members can serveasv a-.broach tc cuti-ts complementary shape in--the other par-t.'I In the embodiment shown; the rungs 3l have corruga tionsy 3a, andv are harder than the metal o-fthe rung holders it. will beclear:- fror-n-v llig-ure` 3, the spacers 6 are providedwith hubs Saw'hichare asat 5bv and 6ctape-red the taper being exaggeratedsomewhat inlthedrawings for the purpose of clarity'. Preferably the major taper 6h converges from theside of the hub whichisl to' be placed on the inside of the ladder toward the outside thereof. As will be seen from Figure 4, the rungs 3 are provided with external corrugations or flutes 3a which serve the double purpose of providing an anti-friction surface as well as elements of the interlock connection between the rungs and the rung holders.

The rungs 3 are hard as compared to the inner surface of the hub 8a of the rung holders. In a practical embodiment of this present invention A the rungs are made of aluminum alloy having a Brinell hardness index of approximately 95 while the spacers are made of an alloy having a Brinell hardness index of 80 or less. It should be mentioned at this point that the rungs 3 are cut from tubular stock of uniform diameter, the ends being pressed or swedged into the tapered hubs of the rung holders 6. In View of the fact that the rungs are harder than the spacers the corrugations or flutes 43a, cut complementary 'grooves in the tapered hub of the spacers. This assembly step causes the end of the rungs which are forced into the tapered hubs of the rung holders 5 to be subjected to very high compressive stresses which, in effect, increases the hardness of the material of which the rungs are made, thereby facilitating the cutting of complementary grooves in the rung holders 6 and produce a very tight, rigid connection between the two parts. In order to retain the rungs and the spacers in assembled relation with the ends of the rungs under very high compressive stresses, the outer end of the rungs are flared by an upsetting operation so that the outer end of the rung at 3b is flared out to engage the reverse taper at 6c. The outwardly flared and 3b of the rung serves the double purpose of holding the taper 6b tightly against the compressed portion of the rung 3 and at the same time reenforce the end of the rung against any tendency to collapse, the result being a very rigid connection between the rungs 3 and the rung holders 6. The opposed joined

tapers

6b and 6c engaged by the complementary shaped end of the rungs 3 constitute a very rigid connection.

It will be apparent that the exact order of the steps in assembling the elements of this ladder is not extremely critical, so long as the elements are assembled in such order and with the parts in such relative position that in the final assembly there are no substantial stresses in the rungs or the side rails and rung holders other than the high compression in the portions of the rungs engaging the taper 6b, the tension in the portion of the rung engaging taper 6c and, of course, the necessary tension stresses in the rung holders 6. It will be noted in this respect that by reason of the fact that the rungs are harder than the rung holders, when the rungs 3 are forced into the hubs of the rung holders the corrugations 3a cut the necessary complementary grooves in the rung holders and the broaching operations which would otherwise be necessary are eliminated and the problem of aligning the corrugations of the rungs and any necessary broached grooves in the spacers is eliminated. Although the rungs are shown as being flared outwardly at 3b, it will be readily apparent to those skilled in the art that other means might be provided for accentuating the compressive stresses in the part of the rung which is fitted to the inside of the hub 8b, such as by means of a tapered plug which could be fitted into the ends of the rungs before the spacers are forced thereon and then the plug could be pulled backwardly toward the outer ends and anchored by any suitable means including rivets or the like extending through the hub 8a and the rungs and any such plug.

In making a ladder in accordance with the present invention the rung holders 5 could be forced onto the ends of the rungs 3 by means of a hydraulic press or the like with a subsequent operation producing the ared outer ends 3b to constitute sub-assemblies which could be thereafter riveted or otherwise fixed to the web elements of the T-sections of the side rail assemblies.

The drawings show a completed ladder assembly in which the rung holders 6, the rungs 3 and the side rail assemblies l and 2 are joined in one unit, but it is fwithin the contemplation of the present invention that sub-assemblies including only the rungs and assembled rung holders equivaent to those shown at 6 could be spaced as desired on any other suitable side rails that a customer might desire. In such instance it would only be necessary to vary the shape of the web portions 6c of the rung holders so that they could be appropriately secured to any type of side rail desired. The important feature of the present invention, as is apparent from the above description, resides in the novel means of attachment of the rung holders 6 to the rungs 3, where only limited area is available, and which is subjected to very high stresses; it being readily understood that there is no particular problem in assembling the rung holders 6 to the side rails of a ladder because there is greater area and therefore the stresses are not so high.

Although the invention has been described in considerable detail, it will be apparent to those skilled in the art that many variations are possible without departing from the inventive concept. It is therefore desired that the invention not be limited except insofar as is made necessary by the prior art and by the appended claims.

What is claimed is:

1. A ladder comprising a plurality of rungs, a plurality of rung holders attached to the ends of said rungs, spaced side rails, said rung holders being secured at intervals between said side rails, said rung holders being provided with hollow hub portions having two adjoined tapered sections diverging from a common minor diameter, the normal outside diameter of said rungs being greater than said minor diameter, said rungs having ends extending throughout said tapered sections and tapered complementary to the tapered bore of said hub portion, said ends having longitudinal corrugations extending into said tapered sections and forming a swedged fit within said tapered sections, the walls of the latter having complementary ridges upset by said corrugations, the outer end of said rung being expanded to fit said reverse taper.

2. A ladder comprising spaced side rails, rung holders secured at intervals between said spaced side rails, said rung holders having a web element xed to said side rails and a hub element serving as a bearing sleeve, said hub element having a tapered bore therein converging toward the outside of said ladder, rung members having a normal outside diameter greater than the smaller diameter of said taper, said rung members having ends tapered complementary to the tapered bore of said hub element and extending throughout said tapered bore, said ends having longitudinal corrugations and being a, swedged iit within said bores maintaining the ends of said rung members s, in a state of high compression within said bores, the walls of the latter having complementary ridges upset by said corrugations, and the extreme outer ends of said rungs being expanded against the outer ends of said sleeves to maintain said rungs tightly in said tapered bores.

3. A ladder as set forth in claim 2 in which said rungs and said rung holders are made of metal alloys and said rungs are made of a metal harder than the metal of said rung holders, said rungs having corrugations which cut complementary grooves in the tapered bores of said rung holders when said rungs are swcdged into said tapered bores.

4. A ladder comprising spaced side rails, rung holders secured at intervals between said spaced side rails, said rung holders having a web element xed to said side rails and a hub element serving as a bearing sleeve, said hub element having a tapered bore therein converging toward the outside of said ladder, rung members having a normal outside diameter greater than the smaller Adiameter of said taper, said rung holders and 'rungs being made of a metallic alloy, said rungs having external corrugations and being of a metal harder than that of said rung holders, said rungs having ends extending throughout said bore and tapered complementary to the tapered bore of said hub element forming a swedged t Within said bores with said ends in a state of high compression, the Walls of said bores having complementary ridges upset by said corrugations, and the extreme outer ends of said rungs being expanded against the outer ends of said sleeves to hold said rungs tightly in said tapered bores.

5. Sub assemblies for use in making a ladder, comprising a, cylindrical ladder rung of metal alloy, rung holders tted to each end of said -rug, each of said rung holders being provided with a hollow hub element, said hub elements ,having a tapered bore therein with joined tapered '.portions diverging in opposite directions, the

` rriinor diameters of which are less than the normal outside diameter of said rung, the ends ofsaid rung extending throughout said tapered v vbore and having tapered sections complementary `to the tapered portions of said bore forming a fswedged fit within said tapered bore with said -fsenvds in a state of high compression, the extreme outer ends of said rung being expanded to engage `'the reverse tapers of said bores.

AUSTIN T. RACE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS