the following description of the invention is provided using a sofa drop - in seat unit as one example or embodiment , however other embodiments , for example , a chair seat box , are contemplated . the invention may be embodied in different forms and should not be construed as limited to the embodiments provided herein . referring to fig1 , there is provided a completed sofa drop - in seat unit or seat box assembly 10 . the drop - in seat unit 10 comprises frame rails 11 , 12 , hooks 14 , springs 40 , and support members 50 . in one embodiment , the frame rails 11 , 12 are generally l - shaped with one frame rail leg 30 positioned perpendicularly to the second frame rail leg 32 , as noted in fig2 a . additional frame rail configurations and hook attachments are contemplated . frame rail leg 32 further includes apertures 34 adapted to receive one end of the hook 14 . hook body segment 15 of the hook 14 lies along the surface of frame rail leg 30 . fig3 provides further detail of the shape of the hook 14 . one end of the hook 14 is curved , curving back upon itself to form the receiving slot 13 for the end of spring 40 . the hook body segment 15 of the hook 14 then bends at approximately 90 degrees ( 90 °), forming a vertical segment 17 of the hook , perpendicular to hook body segment 15 . the vertical hook segment 17 bends again at approximately 90 degrees ( 90 °) in a horizontal direction , parallel and opposite to hook body segment 15 , forming hook end segment 19 . hook body segment 15 and hook end segment 19 are generally parallel to one another . fig4 demonstrates the position of hook 14 as it is affixed to a frame rail 11 , 12 . the hook body segment 15 is disposed adjacent frame rail leg 30 , in a horizontal position , such that the hook receiving slot 13 is oriented upward , positioned to receive a spring end 42 , 44 . the hook vertical segment 17 is disposed adjacent frame rail leg 32 . hook end segment 19 extends through an aperture 34 in the frame rail leg 32 , and bends towards frame rail leg 30 , on the interior of the frame rail 11 , 12 . bending hook segment 19 towards frame rail leg 30 secures hook 14 in place and to the frame rail 11 , 12 . hence , the hooks 14 can be affixed to the frame rails 11 , 12 in a pre - assembly operation and can be shipped to a furniture manufacturer without loss of hooks 14 from the frame rail 11 , 12 or damage to the hooks 14 . as shown in fig5 , hook 14 is affixed to frame rail 11 ( affixed identically to frame rail 12 ) by inserting hook end segment 19 through aperture 34 , and then bending hook end segment 19 towards frame rail leg 30 . a plurality of hooks 14 are affixed to the two frame rails 11 , 12 such that when the two frame rails 11 , 12 are aligned in parallel to each other , the hooks 14 on first frame rail 11 are also aligned in parallel to the hooks 14 affixed to the second frame rail 12 . fig6 shows a plurality of sinusoidal springs 40 that are extended between the two frame rails 11 , 12 . other shaped springs may also be used and are within the scope of the invention . sinusoidal spring 40 contains two spring ends 42 , 44 . the spring ends 42 , 44 , are affixed to hooks 14 that have been affixed to the frame rails 11 , 12 . the frame rails 11 , 12 are oriented in parallel to one another , such that the hooks 14 affixed to the first frame rail 11 are oriented in parallel to the hooks 14 affixed to the second frame rail 12 . sinusoidal spring end 42 is disposed in receiving slot 13 of hook 14 , wherein hook 14 is affixed to first frame rail 11 , and sinusoidal spring end 44 is disposed in receiving slot 13 of hook 14 , wherein hook 14 is affixed to second frame rail 12 . the position of the attached sinusoidal springs 40 relative to the rail frames 11 , 12 is shown in fig1 and 6 . in addition to the plurality of sinusoidal springs 40 extended between the first frame rail 11 and the second frame rail 12 , there is a plurality of support members 50 also extended between the first frame rail 11 and the second frame rail 12 . the support members 50 are generally arcuate , and are positioned among the sinusoidal springs 40 that are affixed to the frame rails 11 , 12 . alternatively , the support members 50 may be other - shaped , such as straight shaped , instead of arcuate . further , alternatively , the support members 50 may be positioned at the ends of the frame rails 11 , 12 , extending between the first frame rail 11 and the second frame rail 12 . in another embodiment , support members 50 may be positioned at the ends of the frame rails 11 , 12 , and other support members 50 may be positioned among the sinusoidal springs 40 that are affixed to the frame rails 11 , 12 . the arcuate shape of the support members 50 provides strength to the drop - in seat unit and the seat . the support members 50 can be of various shaped tubing , but preferably are comprised of square tubing . fig1 shows one embodiment of the frame rails 11 , 12 , with the sinusoidal springs 40 and the arcuate support members 50 affixed to the frame rails 11 , 12 . the frame rails 11 , 12 have a plurality of apertures 52 in frame rail leg 30 , wherein the apertures 52 are adapted to receive a bolt 58 , or other mechanical attachment device , such as a screw , pin , nail , or the like . the arcuate support member 50 has an aperture 54 , 56 disposed at each end 53 , 55 of the arcuate support member 50 . the aperture 54 , 56 is also adapted to receive a bolt 58 . the arcuate support member 50 extends between the frame rails 11 , 12 , connecting the first frame rail 11 to the second frame rail 12 . as shown in fig9 , the support member end 53 is positioned such that the top surface 51 of the support member end 53 abuts frame rail surface 31 , in the interior of the l - shape of the first frame rail 11 . the aperture 52 in the first frame rail 11 is aligned with the aperture 54 in the support member 50 and the bolt 58 is inserted through both apertures 52 , 54 and secured . bolt 58 can be a self - tapping bolt . similarly , the support member end 55 is positioned such that the top surface 51 of the support member end 55 abuts frame rail surface 31 , in the interior of the l - shape of the second frame rail 12 . the aperture 52 in the second frame rail 12 is aligned with the aperture 56 in the support member 50 and the bolt 58 is inserted through both apertures 52 , 56 and secured . the completed drop - in seat unit comprises the frame rails 11 , 12 ; the hooks 14 ; the sinusoidal springs 40 , and the support members 50 which are affixed to the frame rails 11 , 12 by way of bolts 58 . the drop - in seat unit is assembled in a series of steps . the hooks 14 are affixed to the frame rails 11 , 12 by placing the hook body segment 15 along the frame rail leg 30 and inserting the hook end segment 19 through an aperture 34 in the frame rail leg 32 , and bending the hook end segment 19 towards frame surface 31 , on the interior of the frame rail 11 , 12 . a plurality of hooks 14 is affixed to first frame rail 11 and a plurality of hooks is affixed to second frame rail 12 in this manner . as shown in fig1 , the frame rails 11 , 12 are positioned in an apparatus 70 wherein the first frame rail 11 is clamped 72 in one section of the apparatus 70 and the second frame rail 12 is clamped 72 in another section of the apparatus 70 . the blocks representing the frame rails 11 , 12 , of fig1 are representative of the frame rails ; l - shaped frame rails or frame rails of another shape . fig1 depicts l - shaped rails 11 , 12 clamped 72 in apparatus 70 . the frame rails 11 , 12 are clamped in parallel position to each other with a distance d 1 between the frame rails 11 , 12 . the frame rails 11 , 12 are positioned in the apparatus such that the hooks 14 are positioned on the top surface of the frame rails 11 , 12 . once the frame rails 11 , 12 are each clamped 72 in place , a plurality of sinusoidal springs 40 are affixed to the frame rails 11 , 12 . a first end 42 of a sinusoidal spring 40 is inserted in receiving slot 13 of hook 14 on one of the frame rails , e . g . first frame rail 11 . then a similar action is repeated with the other end of the sinusoidal spring 40 in the other frame rail , e . g . frame rail 12 . a second end 44 of the sinusoidal spring 40 is inserted in the receiving slot 13 of the hook 14 on the second frame rail 12 . hence , one end 42 of sinusoidal spring 40 is affixed to the first frame rail 11 and the other end 44 of the sinusoidal spring 40 is affixed to the second frame rail 12 , thereby connecting the two frame rails . after the plurality of sinusoidal springs 40 is attached to the two frame rails 11 , 12 and tapped in place , the apparatus 70 is adjusted to increase the distance d ( d 2 ) between the first frame rail 11 and the second frame rail 12 . hence , the distance d 2 is greater than the distance d 1 . the increase in distance between the frame rails 11 , 12 causes tension to be added to the sinusoidal springs 40 and for the sinusoidal springs 40 to elongate . when the frame rails 11 , 12 are moved to a predetermined separation distance d 2 , then the arcuate support members 50 are added to the drop - in seat unit 10 . a plurality of arcuate support members 50 is affixed between the first frame rail 11 and the second frame rail 12 , bridging the gap between the frame rails 11 , 12 . the top surface 51 of support end 53 is disposed adjacent first frame rail 11 surface 31 , such that top surface 51 of support end 53 abuts first frame rail 11 surface 31 . the aperture 54 in support end 53 is aligned with aperture 52 in first frame rail 11 , and a bolt 58 , preferably a self - tapping bolt 58 , is inserted into the aligned apertures 52 , 54 and fixed . further , the other end of the support member 50 , support end 55 , is disposed adjacent second frame rail 12 surface 31 , such that top surface 51 of support end 55 abuts second frame rail 12 surface 31 . the aperture 56 in support end 55 is aligned with aperture 52 in second frame rail 12 , and a bolt 58 , preferably a self - tapping bolt 58 , is inserted into the aligned apertures 52 , 56 and fixed . in each instance , the support end 53 , 55 is positioned in the interior of the l formed by the two surfaces of the frame rail 11 , 12 . it is understood that the position of the support member is reversible , such that support end 53 can be affixed to second frame rail 12 and support end 55 can be affixed to first frame rail 11 . once the arcuate support members 55 are affixed to the frame rails 11 , 12 , then the apparatus is adjusted such that the clamping devices 72 holding the frame rails 11 , 12 in place are released , and the frame rails 11 , 12 are no longer gripped in the apparatus . the completed drop - in seat unit ( seat box assembly ) is removed from the apparatus and the cycle can begin again with the placement of a first frame rail 11 and a second frame rail 12 in the apparatus 70 and clamping 72 of the frame rails 11 , 12 in place . the method described above allows a worker to construct the drop - in seat unit 10 without the worker having to stretch the sinusoidal springs 40 to be able to attach the sinusoidal springs 40 to the frame rails 11 , 12 after the frame rails 11 , 12 are properly spaced apart . instead , the apparatus 70 provides the force to separate the frame rails 11 , 12 to the appropriate spacing ( d 2 ) after the sinusoidal springs 40 have been attached to the frame rails 11 , 12 . further , no welding is required in the manufacture of the drop - in seat unit . pre - assembled frame rails may be easily nested for stacking , storage or shipping , as shown in fig1 . the pre - assembled frame rails 11 , 12 include the hooks 14 already affixed to the frame rails 11 , 12 . the hooks 14 can be affixed to the frame rails 11 , 12 by the manufacturer of the frame rails 11 , 12 , a job shop or some other party . the pre - assembled frame rails 11 , 12 are stacked for shipping as shown in fig1 . the pre - assembled frame rails 11 , 12 are stacked offset to allow for the hooks 14 , which are fixed to the frame rails 11 , 12 . fig1 a demonstrates the offset position of the hooks 14 , which are fixed to the frame rails 11 , 12 . fig1 a demonstrates not interfere with one another and allow for compact nesting of the pre - assembled frame rails 11 , 12 . the hooks 14 are affixed to the frame rails 11 , 12 , as described above , such that the hooks 14 are “ locked ” to the frame rails 11 , 12 . with the hooks 14 locked onto the frame rails 11 , 12 , the pre - assembled frame rails 11 , 12 can be stacked and transported without the loss of hooks 14 and without a need to use resources to replace missing hooks 14 . the pre - assembled frame rails 11 , 12 can be stacked in various heights and widths , however a preferred configuration is described below . the number of pre - assembled frame rails in the stacks can be varied and still fall within the scope and spirit of the patent . the pre - assembled frame rails 11 , 12 are stacked in three tiers , wherein each tier contains 25 pre - assembled frame rails across the width ( w ) and 12 pre - assembled frame rails 11 , 12 in height ( h ). a dunnage board 62 is placed under the first tier 61 , and the first tier 61 of pre - assembled frame rails 11 , 12 is stacked on the dunnage board 62 . a second dunnage board 62 is placed on the first tier 61 of pre - assembled frame rails 11 , 12 . a second tier 63 of pre - assembled frame rails 11 , 12 is placed on the dunnage board 62 , in the same configuration as the first tier 61 of pre - assembled frame rails 11 , 12 . another dunnage board 62 is placed on top of the second tier 63 of the pre - assembled frame rails 11 , 12 . a third tier 65 of pre - assembled frame rails 11 , 12 is placed on top of the third dunnage board 62 . the third tier 65 of pre - assembled frame rails 11 , 12 is configured similarly to the first and second tiers of pre - assembled frame rails 11 , 12 . a fourth dunnage board 62 is placed on top of the third tier 65 of pre - assembled frame rails 11 , 12 , and forms the top of the frame rail unit 60 . the dunnage board 62 that is utilized in packing the pre - assembled frame rails 11 , 12 is made from mdf , plywood , osb material and the like . further , the dunnage board 62 must be at least 16 mm thick or thicker . the frame rail unit 60 is banded in between the tiers as shown in fig1 . banding the frame rail unit 60 in - between the dunnage boards 62 assists in preventing the pre - assembled frame rails 11 , 12 from shifting during transport . further , the configuration of the bands 64 is conducive to banding a tier , stacking another tier , and banding together those tiers , and so on . the bands 64 are made from corrugated tie sheets and the like . further , the entire frame rail unit 60 is banded with bands 64 extending around the top and the bottom dunnage boards 62 . prior to shipping , the entire frame rail unit 60 is stretch wrapped . the configuration of the frame rail unit 60 provides a compact method of transporting the pre - assembled frame rails 11 , 12 such that there is minimal damage to the pre - assembled frame rails 11 , 12 and the hooks 14 are not displaced due to stacking and remain affixed during transport . further , the configuration of the frame rail unit 60 also allows for stacking of frame rail units 60 for transport . the support members 50 can also be compactly stacked for transport . the number of support members in the stacks can be varied and still fall within the scope and spirit of the patent , however , a preferred configuration is provided below . the support members 50 can be arranged horizontally and stacked on top of each other in vertical stacks of 65 support members , with two such stacks of support members 50 positioned end to end . fig1 a shows the position of the two stacks of 65 support members each . an additional 20 support members 50 are stacked and oriented vertically to the side of the two stacks of 65 support members 50 . fig1 a shows the orientation of the two stacks of 65 support members 50 and the one stack of 20 support members 50 to each other . fig1 b provides a close - up of the orientation of the support members 50 in the packed configuration . the two stacks of 65 support members 50 are oriented horizontally , along with the stack of 20 support members 50 . three such groupings are stacked one on too of the other on a bottom dunnage board 82 . a dunnage board 82 is placed on top of this arrangement of 450 support members ( 3 layers of 130 ; 3 layers of 20 ). then another 450 support members 50 are arranged in the same configuration on top of the dunnage board 82 . a dunnage board 82 is placed on top of this layer of support members 50 , and the support member unit 80 is banded . fig1 shows the orientation of the support member 50 in the packed configuration , with the dunnage boards 82 and bands 84 in place . the dunnage boards 82 used are made from material such as mdf , plywood osb material and the like . the dunnage board 82 is preferably 16 mm thick or thicker . the bands 84 are preferably corrugated tie sheets . once the support member unit 80 is compiled , preferably 6 layers of 150 support members 50 , and banded , the entire support member unit 80 is stretch wrapped for transport . the use of the dunnage board 82 provides a number of benefits , including protecting the support members 50 , keeping the support members 50 from shifting during transport , and being able to stack the support member units 80 . the embodiments above are intended to be illustrative and not limiting . additional embodiments are within the claims . although the present invention has been described with reference to particular embodiments , workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention .
the present invention provides for a drop - in seat unit as well as a method of manufacturing the drop - in seat unit that does not require the worker to affix one end of the spring to a frame rail and stretch the spring from one of the frame rails to the other frame rail . the ends of the spring are affixed to the frame rails while the springs are in an un - stretched state . once the plurality of springs is attached to the two frame rails , the rails are mechanically pulled away from each other , thus creating a larger open area between the frame rails and thus extending the springs . once the rails are properly positioned in this extended state , support members are positioned between the two frame rails and one end of each support member is affixed to each frame rail , traversing the space or gap between the two frame rails . the support members fix the distance between the two frame rails . once the springs are attached to the two frame rails and the support members are affixed to the two frame rails , the completed drop - in seat unit or seat box assembly is unclamped and released from the manufacturing apparatus and is ready for shipment or use in further construction of the sofa or chair .