US 3279051 A
Description (OCR text may contain errors)
Oct. 18, 1966 A. w. MINSHALL 3,279,051 METHOD OF FORMING A JOINT BETWEEN A METAL Filed July 21, 1965 RAIL AND A HOLLOW METAL RUNG 2 Sheets-Sheet 1 FIG. 5
INVENTOR. AUBREY W MINSHALL A tome Oct. 18, 1966 w. MINSHALL 3,279,051
A. METHOD OF FORMING A JOINT BETWEEN A METAL RAIL AND A HOLLOW METAL RUNG Filed July 21, 1965 2 Sheets-Sheet 2 INVENTOR. AUBREY W. M/NSHALL Attorney United States Patent METHOD OF FORMING A JOINT BETWEEN A METAL RAIL AND A HOLLOW METAL RUNG Aubrey Wilson Minshall, 3114 Constitution Blvd., Cooksville, Ontario, Canada Filed July 21, 1965, Ser. No. 473,750
Claims priority, application Canada, Apr. 5, 1965, 927,327 1 Claim. (Cl. 29-512) This invention relates to a method of making a ladder construction and particularly to an improved method of making a metal ladder construction. The invention has particular relation to joining hollow ladder rungs to side rails and where such parts are made from aluminum alloys.
Various side rail and rung connections have been previously employed in metal ladder constructions but to meet the requisite strength under the application of torque it has generally been necessary to incorporate additional members in the joint between the cross rung and side rails; these additional members increase the expense of production and, furthermore, undesirably increase the Weight of a metal ladder when constructed of aluminum alloys.
It is an object of the invention to provide a method of making a ladder joint construction which utilizes only the body of material which forms the ladder rung and side rail and wherein no additional material or parts are incorporated.
It is a further object of the invention to provide a method of making a ladder joint construction which will ensure freedom from failure upon application of the minimum torque stipulated for safety requirements and wherein said joint incorporates only the material of the body of the ladder rung and side rail.
The invention will now be described with reference to the accompanying drawings, in which:
FIGURE 1 is a side view, partly in section, illustrating a preferred manner of swaging a hollow rung adjacent its ends;
FIGURE 2 is a view in section illustrating the step of blanking a side rail;
FIGURE 3 is a perspective view of a preferred configuration of the blank produced by the step illustrated in FIGURE 2;
FIGURE 4 is a view in section illustrating the step of forming a flange to the blank illustrated in FIGURE 3;
FIGURE 5 is a view in section showing a flanged side rail and swaged rung in assembled relation prior to the joining step;
FIGURE 6 is a view in section illustrating the step of coin curling the assembled side rail and swaged rung to form the joint;
FIGURE 7 is a perspective view with part cut away of the joint of the side rail and rung produced according to the invention; and
FIGURE 8 is a perspective view looking towards the inner side of the ladder of an assembled rung and side rail produced according to the invention.
Referring now to the drawings a rung 10 is provided with a shoulder 12 which extends across the perimeter of the rung 10; the shoulder 12 being positioned adjacent one end of the rung 10 leaving an extending outward portion 14. It will be appreciated that a corresponding shoulder 12 will be provided adjacent the other end of the rung 10. To provide both shoulders simultaneously a preferred manner of performing this swaging operation is shown in FIGURE 1; the rung 10 is positioned between a pair of clamps 16 operated by a piston and cylinder structure 18; the ends of the clamps 16 terminate some distance short of the ends of the rung 10 and hollow dies 3,279,051 Patented Oct. 18, 1966 20 of inner configuration corresponding to the outer configuration of the rung 10 are positioned over each end of the latter. The length of each die 20 is such that its open end terminates short of the adjacent end of the clamps 16 when the end of the rung 10 bears against the base 22 of the respective die 20. A cylinder and piston structure 24 is connected to each die 20 and when the clamps 16 closeonto the rung 10 the step of providing the shoulders 12 is completed by actuating the dies 20 inwards to swage the rung 10.
As illustrated in FIGURE 2 the base 26 of the side rail 28 is blanked out by means of a press tool 30 cooperating with a support 32 to provide a cavity 34 somewhat smaller in diameter than the outward portion 14 of the rung 10. The illustrated side rail 28 is intended for a construction of an extension ladder and has outwardly extending flanges 36 and 38, the latter terminating in an inturned member 40. The word outwardly designates a direction away from the rungs 10 in the assembled ladder but the invention is equally applicable to a single ladder wherein the side rail 28 is constructed of a plane memher.
As illustrated in FIGURE 3 the preferred shape formed during blanking by the head of the press tool 30 and cooperating support is such that the circular cavity 34 communicates with radially oriented equally spaced channels 42 of uniform width along their length, thereby providing tongues 44 which taper in the direction of the cavity 34. The length of each of the channels 42 is such that their bases 46, each of which is preferably rounded, rest on the perimeter of a circle whereby the tongues 44 are less than the length of the outward portion 14 of the rung 10. Furthermore, it is preferable for the bases 46 to rest on the perimeter of a circle having a diameter slightly less than the outside diameter of the peripheral shoulder 12.
As illustrated in FIGURE 4 the material adjacent the edge of the cavity 34 is formed outwardly of the base 26 to provide a flange 48 which preferably has a diameter slightly less than the diameter of the rung 10 and at least no greater than the outside diameter of the peripheral shoulder 12. Furthermore, the amount of material formed at the edge of the cavity 34 is such that the depth of the flange 46 is less than the length of the outward portion 14 of the rung 10. In the preferred blanked configuration wherein the tongues 44 are provided this relationship of the depth of the flange 46 to the length of the outward portion 14 will result if the perimeter of the head of the press tool 30 corresponds with the perimeter prescribed by the bases 46 of the channels 42; also the flanging operation of the tongues 44 will be less severe as compared with a flange 46 produced from an integral edge with the result that the amount of work hardening will be reduced thus facilitating the final step described below in the method of the present invention.
After completion of the swaging and flanging steps assembly of the rung 10 and the side rail 28 is elfected. As illustrated in FIGURE 5 the outward portion 14 of the rung 10 is pressed into the flange 48, the outward end 14 of the rung 10 entering the side rail 28 from the side opposed to the flange 48. The rung 10 is held by the clamps 16 and an actuated suitably shaped die 50 presses the side rail 28 along the outward portion 14 until the side rail 28 encounters the peripheral shoulder 12; the assembled relationship of the rung 10 and the side rail 28 is such that the outward portion 14 of the rung 10 terminates beyond the end of the flange 48.
The final step in the method, as illustrated in FIGURE 6, is to bend or coin curl the outward portion 14 of the rung 10 over the flange 48; this is conveniently effected by means of an actuated suitably shaped die 52 which has a tongue 54 which extends with sliding contact into the rung 10 past the shoulder 12 thus providing the requisite support for the rung 10 in co-operation with the external clamps 16. At the root of the tongue 54 the surface of the die 52 flares outwardly with respect to its axis in an arcuate configuration which terminates in a circular abutment 56. When the die 52 is actuated towards the assembled rung 10 and side rail 28, the tongue 54 enters the rung 10 and travels past the shoulder 12; the extremity of the outward portion 14 then meets the arcuate configuration at the root of the tongue 54 and due to the arcuate configuration commences to bend over and eventually in the reverse direction towards the side.
rail 28. With continued movement of the die 52 the flange 48 also begins to bend over in the same direction as the portion 14; the coin curling action is continued until the latter meets the side rail 28 and then completed when the recess between the root of the tongue 54 and the circular abutment 56 is filled with the curled over portion 14 with the flange 48.
By way of example a joint of a rung and a rail made according to the invention was tested under torque and 1,720 inch pounds had to be applied at which level the rung showed twisting but the joint was still intact; in contrast a rung which had simply been swaged onto the side rail loosened on the application of a torque of 590 inch pounds.
While certain embodiments have been illustrated and described for the purpose of disclosure, it will be understood that the invention is not limited thereto, but contemplates such modifications and other embodiments as may be utilized without departing from the invention.
The method of making an integral joint between a hollow metal rung and a metal side rail part comprising the steps of forming an opening having a toothed flange at its perimeter in said metal side part, swaging said rung to form a peripheral abutment on its surface adjacent an end, said abutment being positioned in relation to said end a distance greater than the depth of said toothed flange, inserting said rung through said flange opening whereby said abutment bears against the wall of said side rail opposed to said flange and curl coining in a direction outwards of the centre of said opening the metal of said rung between said abutment and said end over said toothed flange untilsaid end bears against the wall of said side rail opposed to said abutment.
References Cited by the Examiner UNITED STATES PATENTS 1 ,'7 37,780 12/ 1929 Wagenhorst. 3,068,029 12/ 1962 Schwartz 29523 XR FOREIGN PATENTS 587,952 5/ 1947 Great Britain. 845,803 8/ 1960 Great Britain.
CHARLIE T. MOON, Primary Examiner.