US20020100737A1

US20020100737A1 - Telecommunications equipment rack having hemmed upright supports for improved structural stiffness

Info

Publication number: US20020100737A1
Application number: US09/775,092
Authority: US
Inventors: Jonathan Walter; Gilbert Reece; Bryan Caudill
Original assignee: NEWTON INSTRUMENT COMPANY Inc
Current assignee: NEWTON INSTRUMENT COMPANY Inc
Priority date: 2001-02-01
Filing date: 2001-02-01
Publication date: 2002-08-01

Abstract

A rack assembly for mounting telecommunications equipment is provided which utilizes at least one but preferably two upstanding spaced-apart frame members that have at least one but preferably both front and back flanges hemmed in order to provide improved structural stiffness to the rack as well as enhanced distance between the upstanding frame members for mounting digital telecommunications equipment and the like therebetween.

Description

TECHNICAL FIELD

The present invention relates to telecommunications equipment racks used primarily for mounting and housing telecommunications equipment, and more specifically to an improved rack for mounting and housing telecommunications equipment which provides hemmed flange vertical upright supports in lieu of conventional single wall upright supports. The telecommunications equipment rack of the present invention provides an equipment rack that is significantly stiffer than conventional equipment rack designs.

RELATED ART

Telecommunications equipment racks or bays are typically installed in controlled environments, vaults, central switching offices, and remote switch buildings. As is well known to those in the telecommunications field, telecommunications equipment racks or bays can be ordered in many different sizes and configurations. To provide strength and stability, telecommunications equipment racks may be bolted to the floor and tied-off to the ceiling superstructure, and cables and wires may be run from the superstructure directly through the tops of the racks. The telecommunications equipment racks known today can be expected to support fiber optic transmission cable and small scale, fully electronic components in addition to conventional bulky and heavy equipment such as copper wiring and electro-mechanical switching components that have been accommodated in the past by these equipment racks.

Regardless of the use of the telecommunications equipment rack, there is always a need for a rack with improved structural rigidity and greater ease of manufacture than is found in conventional telecommunications equipment racks presently being manufactured and used. This is particularly desirable in localities where the telecommunications racks must adhere to rigid industry standards regarding the ability of the telecommunications equipment racks to withstand seismic forces. For example, racks intended to withstand seismic forces must be designed to comply with BELLCORE Zone 4 for seismic tests as set forth in Document # GR63 CORE. Accordingly, the telecommunications rack of the present invention provides an improved strength telecommunications rack design.

The telecommunications rack of the present invention contemplates the use of hemmed flange uprights that results in double thick upright walls which provide enhanced stiffness to the equipment rack (e.g., enhanced front-to-back stiffness) relative to conventional equipment rack designs. The hemmed flange upright supports can be incorporated into either UFER or network bay design telecommunications equipment racks. Also, the improved equipment rack with hemmed flange upright supports possesses a secondary advantage of having increased space for mounting equipment between the hemmed flange upright supports. This is particularly advantageous for mounting slightly wider digital telecommunications equipment that may not readily mount in conventional telecommunications equipment racks. In other words, the new hemmed flange upright supports provide an advantageous geometry to the improved equipment rack wherein there is provided an increased horizontal space between the hemmed flange upright supports while maintaining conventional horizontal spacing between equipment mounting holes. Summarily, the improved strength telecommunications equipment rack of the present invention is described in detail hereinbelow so that the long-felt need for such an improved strength rack will be fully apparent to one skilled in the art.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided a new rack assembly for mounting telecommunications equipment that is designed so as to provide enhanced front-to-back stiffness as well as increased horizontal space between the upright supports of the rack assembly. The rack assembly of the present invention comprises a pair of upstanding spaced-apart frame members wherein each of the frame members has an upper and a lower end. A horizontal frame member extends between the upper ends of the pair of upstanding spaced-apart frame members, and a base extends between the lower ends of the pair of spaced-apart frame members. The improved rack assembly of the present invention contemplates utilizing at least one (and preferably two) hemmed flange upstanding spaced-apart frame member wherein the spaced-apart frame member comprises a generally U-shaped cross-section defining a web comprising a bottom with a relatively short side portion on one side and a relatively long side portion on the other side, and the upstanding frame member being outwardly directed relative to the other of the pair of upstanding frame members, and wherein at least one (and preferably both) of the relatively short side portion and the relatively long side portion is bent back upon itself so as to create a hemmed side portion or flange to the U-shaped cross-section of the upstanding frame member.

The use of at least one and preferably two of the hemmed upstanding frame members wherein each frame member comprises at least one and preferably two hemmed flanges serves to provide enhanced front-to-back stiffness to the rack assembly as well as increased horizontal space between the pair of upstanding frame members to better accommodate digital equipment therebetween.

Thus it is an object of the present invention to provide an improved telecommunications equipment rack assembly that possesses enhanced front-to-back stiffness.

It is another object of the present invention to provide an improved telecommunications equipment rack assembly that provides for increased horizontal space between the upstanding spaced-apart frame members of the rack assembly to better accommodate digital equipment therebetween.

It is another object of the present invention to provide an improved telecommunications equipment rack assembly that provides for hemmed flange upstanding spaced-apart frame members which can be incorporated into either a UFER or network bay equipment rack design.

It is still another object of the present invention to provide an improved telecommunications equipment rack assembly that incorporates hemmed flange upstanding spaced-apart frame members that provide enhanced strength to the equipment rack and that may be easily manufactured by using conventional manufacturing techniques including: a hemming die in a large press brake; stamping with a set of progressive dyes to create the hemmed profile; and roll-forming by utilizing a series of rolls for forming the hem along the length of the upstanding frame member element.

Some of the objects of the invention having been stated hereinbefore, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a horizontal cross-section view of a prior art upstanding frame member for a telecommunications equipment rack; [0012]
FIG. 2 is a horizontal cross-section view of a first embodiment of the hemmed flange upstanding frame member used in the improved telecommunications equipment rack of the present invention; [0013]
FIG. 3 is a perspective view of the hemmed flange upstanding frame member shown in FIG. 2; [0014]
FIG. 4 is a perspective view of an improved telecommunications equipment rack made in accordance with the present invention and incorporating a spaced-apart pair of hemmed flange upstanding frame members as shown in FIGS. [0015] 2-3;
FIG. 5 shows an enlarged fragmentary view of the base of the improved telecommunications equipment rack of the present invention shown in FIG. 4; [0016]
FIG. 6 is a horizontal cross-section view of a second embodiment of the hemmed flange upstanding frame member used in the improved telecommunications equipment rack of the present invention; [0017]
FIG. 7 is a horizontal cross-section view of a third embodiment of the hemmed flange upstanding frame member used in the improved telecommunications equipment rack of the present invention; and [0018]
FIG. 8 is a horizontal cross-section view of a fourth embodiment of the hemmed flange upstanding frame member used in the improved telecommunications equipment rack of the present invention.[0019]

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

Referring now to FIGS. [0020] 1-8 of the drawings, the improved structural strength equipment rack of the present invention is shown and generally designated 10. Equipment rack 10 is constructed from two upstanding frame members A joined by horizontal metal channel crossbar 12 at the top and a base or base weldment 14 at the bottom thereof to which a network bay base cover (as shown) or UFER base cover (not shown) may be attached by a suitable means such as screws (not shown).
In conventional equipment racks, the pair of upstanding spaced-apart frame members F typically utilize U-shaped channels having a cross-section as best shown in FIG. 1 of the drawings in order to form what is known in the trade as an unequal flange equipment rack. Upstanding frame member F shown in FIG. 1 typically includes a series of vertically spaced-apart apertures F′ in one flange and two series of vertically spaced-apart apertures F′ and F′ in the other flange thereof. The vertically spaced-apart apertures F′ in the back and front flanges of upstanding frame member F are used to mount selected telecommunications equipment between upstanding spaced-apart frame members F. It should be appreciated that although a network bay base is shown with [0021] equipment rack 10, the present invention contemplates that equipment rack 10 can also be a UFER base equipment rack of the type well known to those skilled in the art. Also, many other configurations of apertures can be provided in frame members F as a matter of design choice.
Referring again to improved [0022] equipment rack 10 best shown in FIGS. 4 and 5 of the drawings, it will be appreciated that the upstanding spaced-apart frame members of equipment rack 10 consist of hemmed flange frame member A as best seen in FIGS. 2-5 of the drawings in lieu of conventional U-shaped frame member F shown in FIG. 1 of the drawings. Hemmed flange upstanding frame member A shown in FIGS. 2-5 is formed from a flat sheet of steel (e.g., one-eighth inch thickness steel) that has been folded over onto itself on each side thereof so as to create a double thickness short or back flange BF and long or front flange FF. The hemmed flange upstanding frame member A as shown in FIG. 2 when utilized in equipment rack 10 provides for a stiffer equipment rack than the conventional pair of upstanding frame members F (see FIG. 1) utilized in prior art unequal flange equipment racks.
It has been discovered that improved [0023] equipment rack 10 of the present invention incorporating a pair of hemmed flange upstanding frame members A is approximately fourteen percent (14.0%) stiffer (e.g., front-to-back stiffness) than conventional unequal flange equipment racks. Moreover, an additional advantage of incorporation of novel hemmed flange upstanding frame members A into equipment rack 10 is an increased horizontal space that is provided between the upstanding pair of frame members due to the positioning of apertures A′ closer to the plane of the inside wall Al of upstanding frame members A than can be accomplished with conventional unequal flange upstanding frame members F (see FIG. 1). This increased horizontal space can be used to better accommodate digital equipment in rack 10.
Referring now to FIG. 2 of the drawings to more specifically describe the structure of hemmed upstanding frame members A it can be seen that hemmed upstanding frame member A consists of a generally U-shaped cross-section comprising a web A[0024] 1 at the bottom with a relatively short side portion on one side and relatively long side portion on the other side wherein both the relatively short side portion and the relatively long side portion are bent back upon themselves so as to create relatively short hemmed flange side portion BF and relatively long hemmed flange side portion FF. The length of relatively short side portion BF that is bent back upon itself is parallel to the remaining length of relatively short side portion BF and the length of the relatively long side portion FF that is bent back upon itself as parallel to the remaining length of the relatively long side portion FF. Further, upstanding frame members A are formed from a generally U-shaped cross-section consisting of web A1 along the bottom length and a first and second bend to form the relatively short side portion on one side that is then bent back upon itself at a third bend to create relatively short hemmed flange side portion BF and a first and second bend to form the relatively long side portion on the other side of the upstanding frame member that is then bent back upon itself at a third bend to create the relatively long hemmed flange side portion FF. Thus, upstanding frame members A (see FIG. 2) are formed of a sheet of steel (preferably ⅛ inch thick) having six bends and seven wall segments A1, A2, A3, A4, A5, A6, A7 to form unequal flange upstanding frame members A that impart the enhanced stiffness to the frame of equipment rack 10.
To better appreciate the ability of improved [0025] equipment rack 10 to provide increased horizontal space between upstanding frame members A due to the unique construction of upstanding frame members A, it should be understood that conventional unequal flange equipment racks formed from a pair of conventional upstanding frame members F (see FIG. 1) provide adequate mounting hole and upright spacing for conventional 21.5 inch and 17.5 inch wide telecommunications equipment. However, as is well known to those skilled in the telecommunications equipment rack art, as digital information transfer becomes more common in traditional central switching office environments, so does the requirement to house digital equipment in unequal flange telecommunications equipment racks. However digital equipment is often 0.25 inches wider (e.g., 21.75 inches and 17.75 wide) than previous telecommunications non-digital switching equipment, while maintaining the same equipment mounting hole distances of 22.312 inches and 18.312 inches. Thus, conventional equipment racks will many times not accommodate digital telecommunications equipment.
In order to accommodate digital telecommunications equipment, an equipment rack must provide the additional 0.25 inches in width while maintaining the mounting hole spacing the same as in conventional equipment racks. This can result in a problem since the tapped mounting holes F′ of the upright channels would have to be moved closer to the bend (see FIG. 1) at the inside front and rear corners of a conventional rack. However, due to material deformation caused by the local bending of the metal of the conventional upright channels F, the mounting holes or apertures F′ therein would tend to deform to such an extent as to be rendered unusable if moved closer to the bend. This problem is solved with improved [0026] equipment rack 10 of the present invention by utilizing upstanding frame members A which by virtue of their hemmed construction allow mounting holes or apertures A′ to be relatively closer to the inner wall A1 of upstanding frame members A (see FIG. 2 of the drawings). Therefore, the mounting space between upstanding frame members A can be increased by the desired 0.25 inches in width to accommodate mounting of digital telecommunications equipment therebetween while the horizontal distance between mounting apertures A′ is maintained the same by laterally shifting of mounting apertures A′ inwardly toward the equipment side of hemmed upstanding frame members A.
Hemmed upstanding frame members A can be manufactured in a number of conventional techniques which would be known to those familiar with metal bending and formation. For example, the simplest way to create hemmed upstanding frame members A is to use a hemming dye in a large press brake which causes the metal to fold back onto itself and thereby create the desired hem at the front and back side of the upstanding frame members. The hemmed upstanding frame members can also be manufactured by stamping using a set of progressive dies to create the hemmed profile of upstanding frame members A. A third technique to achieve the desired shape is by roll-forming the hem at the front and back of upstanding frame members A by utilizing a series of rolls along the length of the elements. [0027]
It should be appreciated that the present invention contemplates the use of at least one and preferably a pair of upstanding hemmed frame members in a telecommunications equipment rack of either the UFER or network bay type. Also, the invention further contemplates the use of at least one and preferably a pair of the hemmed upstanding frame members not only in unequal flange-type equipment racks but in any type of telecommunications equipment rack into which they may be incorporated for enhanced structural strength. [0028]

Alternative Embodiments

Referring now to FIGS. [0029] 6-8 of the drawings, three (3) alternative embodiments of the upstanding frame members A utilized in the improved equipment rack 10 of the present invention are shown and generally designated AA, AAA, AAAA, respectively. At least one upstanding frame member AA, AAA, AAAA and preferably a pair would be used in equipment rack 10.
Frame member AA shown in FIG. 6 comprises a generally U-shaped four bend and five wall segment AA[0030] 1, AA2, AA3, AA4, AA5 cross-section comprising a web AA1 having a bottom length and a first bend to form the relatively short side portion on one side that is then bent back upon itself to create the relatively short hemmed flange side portion and having a first bend to form the relatively long side portion on the other side of the frame member that is then bent back upon itself to create the relatively long hemmed flange side portion of the frame member. Frame member AA provides many of the benefits of frame member F shown in FIG. 1 and should be easier to manufacture.
Upstanding frame member AA shown in FIG. 6 comprising four bends and five wall segments also includes a vertical series of spaced-apart apertures AA′ formed in the front flange thereof. As with respect to frame member A, one or more vertical series of spaced-apart apertures would also normally be included in the back flange of frame member AA. [0031]
A third embodiment of upstanding frame members A utilized in [0032] improved equipment rack 10 of the present invention is shown and generally designated AAA in FIG. 7 of the drawings. Frame member AAA comprises a generally U-shaped four bend and five wall segment AAA1, AAA2, AAA3, AAA4, AAA5 cross-section comprising a web AAA1 having a bottom length and a first bend to form one side portion that is then bent back upon itself to create one hemmed flange side portion and having a first bend to form the second side portion on the other side of the frame member that is then bent back upon itself to create the second hemmed flange side portion of frame member AAA. The front and back hemmed flanges of frame member AAA are of equal length as can best be seen with reference to FIG. 7.
Finally, a fourth embodiment of the upstanding frame members A utilized in [0033] improved equipment rack 10 of the present invention is shown and generally designated AAAA in FIG. 8. Frame member AAAA comprises a generally U-shaped five bend and six wall segment AAAA1, AAAA2, AAAA3, AAAA4, AAAA5, AAAA6 cross-section comprising web AAAA1 having a bottom length and a first and second bend to form the relatively short side portion on one side that is then bent back upon itself to create a relatively short hemmed flange side portion and having a first bend to form the relatively long side portion on the other side of frame member AAAA that is then bent normally thereto to create the relatively long non-hemmed flange side portion of frame member AAAA. Thus, frame member AAAA is formed with only one flange hinged and the other flange formed similarly to the long flange of conventional frame member F shown in FIG. 1. It is presently contemplated that frame member AAAA will only be provided with apertures AAA′ in the hemmed flange thereof.
It should be appreciated that while the four embodiments of the hemmed upstanding frame members utilized in [0034] improved equipment rack 10 of the present invention are shown in FIGS. 2-8 of the drawings with specific aperture mounting holes or apertures therein, the placement of apertures in each of the four embodiments of the upstanding frame members can be varied from that depicted in the drawings which are intended as representative only and not to limit the scope of the invention which is defined by the claims appended hereto.
It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims. [0035]

Claims

What is claimed is:

1. In a rack assembly for mounting telecommunications equipment of the type comprising a pair of upstanding spaced-apart frame members wherein each of said frame members defines an upper and a lower end; a horizontal frame member extending between the upper ends of said pair of upstanding spaced-apart frame members; and a base extending between the lower ends of said pair of upstanding spaced-apart frame members; the improvement wherein at least one of said pair of upstanding spaced-apart frame members comprises:

an upstanding spaced-apart frame member with a generally U-shaped cross-section comprising a web having a bottom with a relatively short side portion on one side and a relatively long side portion on the other side and said frame member being outwardly directed relative to the other of said pair of frame members, and wherein at least one of said relatively short side portion and said relatively long side portion is bent back upon itself so as to create a hemmed flange side portion;

wherein the rack assembly possesses enhanced structural strength.

2. The rack assembly according to claim 1 wherein the length of the side portion bent back upon itself is parallel to the remaining length of the side portion.

3. The rack assembly according to claim 1 wherein the at least one of said pair of upstanding spaced-apart frame members comprises a generally U-shaped cross-section comprising a web having a bottom length and a first and second bend to form the relatively short side portion on one side that is then bent back upon itself to create the relatively short hemmed side portion and having a first and second bend to form the relatively long side portion on the other side of the frame member that is then bent back upon itself to create the relatively long hemmed side portion of said frame member.

4. The rack assembly according to claim 3 wherein the frame member is formed of steel having six bends and seven wall segments.

5. The rack assembly according to claim 4 wherein the frame member is formed of one-eighth inch thick steel.

6. The rack assembly according to claim 1 wherein the at least one of said pair of upstanding spaced-apart frame members comprises a generally U-shaped cross-section comprising a web having a bottom length and a first bend to form the relatively short side portion on one side that is then bent back upon itself to create the relatively short hemmed side portion and having a first bend to form the relatively long side portion on the other side of the frame member that is then bent back upon itself to create the relatively long hemmed side portion of said frame member.

7. The rack assembly according to claim 6 wherein the frame member is formed of steel having four bends and five wall segments.

8. The rack assembly according to claim 7 wherein the frame member is formed of one-eighth inch thick steel.

9. In a rack assembly for mounting telecommunications equipment of the type comprising a pair of upstanding spaced-apart frame members wherein each of said frame members defines an upper and a lower end; a horizontal frame member extending between the upper ends of said pair of upstanding spaced-apart frame members; and a base extending between the lower ends of said pair of upstanding spaced-apart frame members; the improvement wherein at least one of said pair of upstanding spaced-apart frame members comprises:

an upstanding spaced-apart frame member with a generally U-shaped six bend and seven wall segment cross-section comprising a web having a bottom length and a first and second bend to form the relatively short side portion on one side that is then bent back upon itself to create the relatively short hemmed side portion and having a first and second bend to form the relatively long side portion on the other side of the frame member that is then bent back upon itself to create the relatively long hemmed side portion of said frame member;

wherein the rack assembly possesses enhanced structural strength.

10. The rack assembly according to claim 9 wherein the length of the relatively short side portion bent back upon itself is parallel to the remaining length of the relatively short side portion and the length of the relatively long side portion bent back upon itself is parallel to the remaining length of the relatively long side portion.

11. In a rack assembly for mounting telecommunications equipment of the type comprising a pair of upstanding spaced-apart frame members wherein each of said frame members defines an upper and a lower end; a horizontal frame member extending between the upper ends of said pair of upstanding spaced-apart frame members; and a base extending between the lower ends of said pair of upstanding spaced-apart frame members; the improvement wherein at least one of said pair of upstanding spaced-apart-frame members comprises:

an upstanding spaced-apart frame member with a generally U-shaped four bend and five wall segment cross-section comprising a web having a bottom length and a first bend to form the relatively short side portion on one side that is then bent back upon itself to create the relatively short hemmed side portion and having a first bend to form the relatively long side portion on the other side of the frame member that is then back upon itself to create the relatively long hemmed side portion of said frame member;

wherein the rack assembly possesses enhanced structural strength.

12. The rack assembly according to claim 11 wherein the length of the relatively short side portion bent back upon itself is parallel to the remaining length of the relatively short side portion and the length of the relatively long side portion bent back upon itself is parallel to the remaining length of the relatively long side portion.

13. In a rack assembly for mounting telecommunications equipment of the type comprising a pair of upstanding spaced-apart frame members wherein each of said frame members defines an upper and a lower end; a horizontal frame member extending between the upper ends of said pair of upstanding spaced-apart frame members; and a base extending between the lower ends of said pair of upstanding spaced-apart frame members; the improvement wherein at least one of said pair of upstanding spaced-apart frame members comprises:

an upstanding spaced-apart frame member with a generally U-shaped cross-section comprising a web having a bottom with a first side portion on one side and a second side portion on the other side and said frame member being outwardly directed relative to the other of said pair of frame members, and wherein each of said first and second side portions is bent back upon itself so as to create a hemmed flange side portion;

wherein the rack assembly possesses enhanced structural strength.

14. The rack assembly according to claim 13 wherein the length of the first side portion bent back upon itself is parallel to the remaining length of the first side portion and the length of the second side portion bent back upon itself is parallel to the remaining length of the second long side portion.

15. The rack assembly according to claim 13 wherein the at least one of said pair of upstanding spaced-apart frame members comprises a generally U-shaped cross-section comprising a web having a bottom length and a first and second bend to form the first side portion on one side that is then bent back upon itself to create the first hemmed flange side portion and having a first and second bend to form the second side portion on the other side of the frame member that is then bent back upon itself to create the second hemmed flange side portion of said frame member.

16. The rack assembly according to claim 15 wherein the frame member is formed of steel having six bends and seven wall segments.

17. The rack assembly according to claim 13 wherein the at least one of said pair of upstanding spaced-apart frame members comprises a generally U-shaped cross-section comprising a web having a bottom length and a first bend to form the first side portion on one side that is then bent back upon itself to create the first hemmed flange side portion and having a first bend to form the second side portion on the other side of the frame member that is then bent back upon itself to create the second hemmed flange portion of said frame member.

18. The rack assembly according to claim 17 wherein the frame member is formed of steel having four bends and five wall segments.

19. In a rack assembly for mounting telecommunications equipment of the type comprising a pair of upstanding spaced-apart frame members wherein each of said frame members defines an upper and a lower end; a horizontal frame member extending between the upper ends of said pair of upstanding spaced-apart frame members; and a base extending between the lower ends of said pair of upstanding spaced-apart frame members; the improvement wherein at least one of said pair of upstanding spaced-apart frame members comprises:

an upstanding spaced-apart frame member with a generally U-shaped cross-section comprising a web having a first side portion on one side that is then bent back upon itself to create a first hemmed side portion and having a second side portion on the other side of the frame member that is then back upon itself to create a second hemmed side portion of said frame member that is equal in length to the first hemmed side portion;

wherein the rack assembly possesses enhanced structural strength.

20. The rack assembly according to claim 19 wherein the length of the first side portion bent back upon itself is parallel to the remaining length of the first side portion and the length of the second side portion bent back upon itself is parallel to the remaining length of the second side portion.

21. In a rack assembly for mounting telecommunications equipment of the type comprising a pair of upstanding spaced-apart frame members wherein each of said frame members defines an upper and a lower end; a horizontal frame member extending between the upper ends of said pair of upstanding spaced-apart frame members; and a base extending between the lower ends of said pair of upstanding spaced-apart frame members; the improvement wherein at least one of said pair of upstanding spaced-apart-frame members comprises:

an upstanding spaced-apart frame member with a generally U-shaped cross-section comprising a web having a bottom length and a first side portion on one side that is bent back upon itself to create a hemmed side portion and a second side portion on the other side of the frame member that forms a non-hemmed side portion;

wherein the rack assembly possesses enhanced structural strength.

22. The rack assembly according to claim 21 wherein the hemmed side portion is shorter than the non-hemmed side portion.