APPARATUS AND METHOD FOR FABRICATING WOOD TRUSSES

Description Apparatus and Method for Fabricating Wood Trusses

Technical Field The present invention relates generally to wood trusses used in building construction and in particular to an apparatus and method for fabricating wood trusses. Background Art

According to prior practice, wood trusses may be fabricated by placing the top and bottom chords in position on a movable support surface, such as a truss assembly jig, and by attaching the vertical connector members and web members between the chords with corrugated fasteners or nails to hold the vertical connector members and web members in position. Stop members are typically positioned in contact with the top and bottom chords along the respective outer surfaces thereof to hold the truss members securely in position on the moveable surface of the jig.

A first set of connector plates is placed over the joints at which the vertical connector members and web members intersect the top and bottom chords on the upwardly facing surface of the truss and tapped so that the teeth of the connector plates are slightly imbedded into the wood to hold them in place. A lifting device is then used to raise the truss from the support surface sufficiently to place a second set of connector plates under the truss on the joints on the downwardly facing surface of the truss at substantially the same locations as on the upwardly facing surface thereof. At this stage, connector plates are positioned on the truss joints on both the upwardly and downwardly facing surfaces thereof, with the second set of connector plates positioned between the downwardly facing surface of the truss and the moveable support surface.

The truss is then carried by the support surface into one or more pressing stations, which are comprised of one or more pairs of pressing rollers, whereby the connector plates are embedded into the wooden members at the truss joints as the truss is passed between each pair of rollers. Camber is typically imparted to the truss by a plurality of camber rollers positioned downstream of the first pressing station. Apparatus and methods known in the art for fabricating wood trusses have several disadvantages and limitations. One problem associated with such prior art apparatus and methods is that the first pair of pressing rollers typically has a substantially smaller diameter than the sets of pressing rollers located downstream. The first pair of pressing rollers is used to partially embed the teeth of the connector plates into the wood members of the truss. The relatively abrupt curvature of the roller surface, as compared to the larger diameter rollers located downstream, may impart a rocking motion to the connector plates, which prevents the teeth from being pressed straight into the wood members.

Another problem associated with such prior art truss assembly apparatus and methods is the problem of controlling the amount of camber applied to the truss. It is often difficult to produce a consistent, predetermined camber because of the difficulty in properly positioning the camber rollers and in maintaining the camber rollers in position. The mechanism used to position the camber rollers is subjected to large mechanical stresses when the truss is being cambered, which may result in slippage and free play in the camber roller positioning mechanism. S t i l l another problem associated with prior art apparatus and methods of fabricating trusses is the problem of maintaining the truss in proper alignment as the truss passes through the various stages of pressing rollers and through the camber rollers. In order to securely attach the connector plates, the truss must be moved from the support surface of the jig before the truss enters the final pressing station. Misalignment of the truss as it passes through the final pressing station causes critical errors in the fabrication of the truss.

Disclosure of Invention

It is therefore the principal object of the present invention to provide an approved apparatus and method for fabricating wood trusses.

It is another object of the invention to provide an improved apparatus and method for imparting camber to a wood truss.

It is still another object of the invention to provide an apparatus and method for enhancing the precision and consistency of the camber imparted to a wood truss.

It is yet another object of the invention to provide an improved apparatus and method for attaching metal connector plates to the joints of a wooden truss.

A further object of the invention is to provide an improved apparatus for maintaining the truss substantially in proper alignment during the fabrication of the truss. These and other objects are accomplished in accordance with the present invention wherein an apparatus and method for fabricating truss members into a completed truss is provided. The truss members are comprised of a plurality of wood members and a plurality of metal connector plates for joining the wood members. The apparatus includes a relatively flat conveyor surface for supporting the truss members with the connector plates positioned below and on top of the wood member; means for moving the conveyor surface with the truss members supported thereon in a predetermined direction; a first pressing station having at least one pair of pressing rollers disposed substantially in registration for receiving the truss members therebetween to partially embed the connector plates into the wood members; and a second pressing station spaced from the first pressing station and beyond the conveyor surface. The second pressing station has a pair of pressing rollers disposed substantially in registration for receiving the truss members therebetween to substantially fully embed the connector plates into the wood members to complete fabrication of the truss. In accordance with one aspect of the invention, the pressing rollers of the second pressing station have substantially the same size as the pressing rollers of the first pressing station. In one embodiment all of the pressing rollers have a substantially cylindrical shape and the diameter of all of the pressing rollers is as large as practicable in accordance with the spatial constraints of the apparatus. In the preferred embodiment each of the pressing rollers has a diameter of at least ten inches. The use of relatively large diameter pressing rollers in both the first and second pressing stations has the advantage of pressing the connector plates into the wood members straighter than when smaller diameter rollers are used because larger diameter rollers impart substantially less rocking action on the front and back ends of the connector plates than do the smaller diameter rollers.

In accordance with another aspect of the invention, the apparatus includes a plurality of elongated guide rails extending along the predetermined direction of movement of the truss beneath the conveyor surface for supporting the conveyor surface and the truss members. At least one of the guide rails extends beyond the first pressing station to maintain the alignment of the conveyor surface. In one embodiment the plurality of guide rails is comprised of a central guide rail and two outer guide rails. The two outer guide rails extend beyond the first pressing station to maintain conveyor surface alignment. The conveyor surface preferably includes a plurality of cooperating pairs of guide rollers positioned on an underside thereof for contacting respective opposite sides of one of the outer guide rails to maintain conveyor surface alignment. In another embodiment the plurality of guide rails is compr'ised of two outer guide rails positioned adjacent to respective opposite edges of the conveyor surface and two inside guide rails disposed between the two outer guide rails. The two outer guide rails extend beyond the first pressing station to maintain the conveyor surface alignment. When four guide rails are used, the conveyor surface has a plurality of cooperating pairs of guide rollers disposed on an underside thereof. The guide rollers of each cooperating pair contact the respective outer surfaces of the two outside guide rails to maintain the conveyor surface in alignment.

In yet another aspect of the invention, a lifting roller is disposed between the first and second pressing stations for engaging an underside of a leading portion of the truss for maintaining the vertical position of the truss as the truss is moved between the first and second pressing stations.

In accordance with a further aspect of the invention, the apparatus includes means for selectively imparting camber to the truss. Switch means is positioned between the first pressing station and the camber means for disabling the operation of the apparatus when the switch means is activated by contact with the truss. The switch means is positioned so that the truss will only contact the switch means when the truss is improperly aligned with respect to the camber means. In one embodiment the switch means includes a projection member which is positioned to contact the truss when the truss is out of alignment. In another embodiment the position of the switch means is adjustable along an axis which is transverse with respect to the predetermined direction of movement of the truss to conform to the width of the truss as measured along the transverse axis. In yet another embodiment the camber means is comprised of first, second, third and fourth camber rollers. The first and second camber rollers contact the top chord and the third and fourth camber rollers contact the bottom chord of the truss to apply a bending moment thereto. The third and fourth camber rollers are adjustable along the transverse axis to conform to the width of the truss. The switch means is mechanically coupled to the third camber roller so that the position of the switch means is adjustable along the transverse axis together with the third camber roller.

In accordance with yet another aspect of the invention, the first and second camber rollers are mounted on a first surface of an arm member, which is pivotally mounted adjacent to a first side of the apparatus and beyond the conveyor surface and the third and fourth camber rollers are positioned adjacent to a second side of the apparatus, opposite from the first side thereof. The first and second camber rollers are out of alignment with respect to an axis which is parallel to the predetermined direction of movement of the truss when the arm member is pivoted from a first position at which the arm member is substantially parallel to the predetermined direction. The amount of displacement of the arm member from the first position determines the amount of camber imparted to the truss. Adjustment means is provided for selectively pivoting the arm member to position the arm member to impart the predetermined amount of camber and engagement means is provided for preventing the arm member from pivoting back toward the first position after the arm member has been pivoted away from the first position, thereby counteracting torque exerted on the arm member by the truss tending to bend the arm member back toward the first position. In the preferred embodiment, the engagement means is comprised of a threaded member, one end of which engages a second surface of the arm member, which is opposite from the first surface thereof on which the first and second camber rollers are mounted. The rotation of the threaded member in a first direction moves the threaded member toward the second surface of the arm member to engage the arm member and prevent it from being moved back toward the first position. The rotation of the threaded member in a second direction, opposite from the first direction, moves the threaded member away from the second surface of the arm member to allow the arm member to be moved back toward the first position.

In accordance with still another aspect of the invention the third and fourth camber rollers are maintained substantially in alignment along an axis which is parallel to the predetermined direction of movement of the truss. Means for adjusting the position of the third and fourth camber rollers laterally with respect to the predetermined direction of the truss is provided so that the third and fourth camber rollers are movable substantially in unison in each direction along the lateral axis. In one embodiment the adjustment means is comprised of first and second spaced apart vertical arms, each of which has a threaded sleeve at each end thereof. The third camber roller is mounted on the first vertical arm and the second camber roller is mounted on the second vertical arm. First and second cooperating pairs of threaded shafts extend laterally with respect to the predetermined direction of movement of the truss. The individual shafts in the first cooperating pair extend through corresponding sleeves on the first vertical arm so that the shaft threads engage complementary threads in the corresponding sleeves. The individual shafts in the second cooperating pair extend through corresponding sleeves on the second vertical arm so that the shaft threads engage complementary threads in the corresponding sleeves. Means for rotating the first and second cooperating pairs of shafts in unison is provided so that the engagement between the shaft threads and the sleeve threads results in movement of the first and second vertical arms and the corresponding third and fourth camber rollers laterally along the corresponding shafts.

In accordance with a further aspect of the invention, the apparatus includes drive means for moving the conveyor surface with the truss members supported thereon in a predetermined direction. The drive means is comprised of first and second chain and sprocket drives in spaced parallel relationship. Each of the chain and sprocket drives has first and second end sprockets with a drive chain disposed on the end sprockets to define a continuous loop drive. The first end sprocket of the first chain and sprocket drive is substantially aligned with the corresponding first end sprocket of the second chain and sprocket drive along a first axis extending laterally with respect to the predetermined direction and the second end sprocket of the first chain and sprocket drive is substantially aligned with the corresponding second end sprocket of the second chain and sprocket drive along a second axis extending laterally with respect to the predetermined direction. A first plurality of elongated members extends laterally with respect to the predetermined direction for connecting the corresponding first end sprockets and a second plurality of elongated members extends laterally with respect to the predetermined direction for connecting the corresponding second end sprockets. The elongated members are substantially rigid for maintaining the corresponding first end sprockets in substantially parallel relationship and the corresponding second end sprockets in substantially parallel relationship.

In yet another aspect of the invention camber is imparted to the truss by providing a relatively flat surface for supporting the wood members of the truss; mounting first and second sets of restraining members at selected fixed positions on the support surface so that the restraining members define a boundary corresponding to the desired configuration of the truss to be cambered; and placing the wood members on the support surface within the boundary defined by the restraining members so that the connector plates are disposed below and on top of the wood members. Web members are connected to the top and bottom chords to urge the chords into contact with corresponding ones of the restraining members so that an outwardly facing surface of the top chord contacts respective inwardly facing surfaces of the first set of restraining members and an outwardly facing surface of the bottom chord contacts respective inwardly facing surfaces of the second set of restraining members, so that the restraining members exert a bending moment on the top and bottom chords to impart camber to the truss.

In the preferred embodiment the support surface is comprised of a plurality of elongated slats oriented transversely with respect to the major axis of the support surface. Selected ones of the slats have a plurality of openings spaced at predetermined intervals along the respective major axes of the corresponding slats. Corresponding openings of adjacent ones of the slats are offset relative to one another along the respective major axes of the corresponding slats so that imaginary line segments connecting the corresponding openings define a curve representing the desired amount of camber to be imparted to the truss. The restraining members have respective base portions with a plurality of holes extending therethrough. Selected ones of the holes are positioned in registration with selected ones of the openings in the corresponding slats for mounting the restraining members thereon. In accordance with the present invention camber is imparted to the truss prior to the attachment of the metal connector plates, which facilitates the cambering operating, particularly when heavy duty trusses are being fabricated for commercial applications.

Brief Description of the Drawings

Further objects and advantages of the invention will be apparent from the detailed description and claims when read in conjunction with the accompanying drawings wherein: FIGURE 1 is a perspective view of an apparatus for fabricating a wood truss in accordance with the present invention;

FIGURE 2 is a top plan view of the apparatus of FIGURE 1, emphasizing selected portions of the apparatus; FIGURE 3A is a side elevation view of a first embodiment of the apparatus according to the present invention;

FIGURE 3B is a side elevation view of a portion of a second embodiment of the apparatus;

FIGURE 4 is an end elevation view of the apparatus according to the present invention, viewed from the discharge or downstream end of the apparatus;

FIGURE 5 is a side elevation view of a portion of the apparatus, illustrating means for lifting the truss as it passes through the pressing stations in the apparatus; FIGURE 6 is a top plan, partial cutaway view, illustrating the mechanism by which selected ones of the camber rollers are positioned to impart predetermined camber to the truss;

FIGURE 7 is a side elevation view, illustrating the positioning of a cut-off switch for stopping the operation of the apparatus when the truss is out of alignment; FIGURE 8 is an end elevation view, illustrating three guide rails beneath the movable support surface of the apparatus;

FIGURE 9 is a top plan view of the table section of the apparatus on which the truss members are disposed, illustrating the means by which camber is imparted to the truss prior to the attachment of the metal connector plates;

FIGURE 10 is a top plan view detailing a portion of the apparatus and truss depicted in FIGURE 9;

FIGURE 11 is a perspective view of a portion of a chain and sprocket drive system for the apparatus; and

FIGURE 12 is a circuit diagram illustrating means for selectively enabling and disabling the apparatus; and

FIGURE 13 is an end elevation view, illustrating three chain drives and four guide rails beneath the moveable support surface of the apparatus.

Best Mode for Carrying Out the Invention

In the description which follows like parts are marked throughout the specification and drawings, respectively.

The drawings are not necessarily to scale and in some instances proportions have been exaggerated in order to more clearly depict certain features of the invention.

Referring to FIGURES 1, 2, 3A and 4, an apparatus 10 for fabricating wood trusses in accordance with the present invention is comprised of a table section 12 and a head section 14. Table section 12 includes a motor-driven conveyor, which is preferably comprised of a pair of parallel, continuous loop chain and sprocket drives 16A and 16B, which are attached to the respective undersurfaces of a plurality of parallel steel slats 18, which define conveyor surface 19 of table section 12. Selected ones of slats 18 have a plurality of pre-drilled threaded holes (not shown) therein for positioning a plurality of tooling blocks (as -11- will be described in greater detail hereinafter with reference to FIGURE 9) on the corresponding top surfaces thereof for anchoring the chords of the truss while the web members and vertical connector members are placed therebetween. The actual placement of the tooling blocks is adjusted to fit the dimensions of the truss being assembled. Head section 14 has a first pressing station with first and second pairs of press rollers 20 and 22, respectively, for partially embedding the connector plates into the truss members as the truss passes between each pair of rollers 20 and 22. Roller pairs 20 and 22 are comprised of respective top rollers 20A and' 22A and bottom rollers 20B and 22B for exerting a pressing force in a direction which is substantially perpendicular to the plane of movable conveyor surface 19. Top rollers 20A and 22A are independently adjustable along a vertical axis to adjust the spacing between each top roller 20A and 22A and its corresponding bottom roller 20B and 22B to conform to the thickness of the truss being fabricated. The vertical adjustment of top rollers 20A and 22A is accomplished in a conventional manner, such as by means of a screw-operated adjustment mechanism, as described in U. S. Patent No. 3,667,379, which description is incorporated by reference herein.

A second pressing station, located downstream of the first pressing station, includes a third pair of rollers 24, which is comprised of a corresponding top roller 24A and bottom roller 24B for completing the attachment of the connector plates to the truss members after the predetermined camber has been applied to the truss. The connector plates must be embedded into the truss by first and second sets of rollers 20 and 22 sufficiently to ensure that the plates are not dislodged during the cambering operation and yet not so much as to prevent the camber rollers from imparting the desired amount of camber to the truss. Camber is applied to the truss by means of four camber rollers 26, 28, 30 and 32. Camber rollers 26 and 28 engage the top chord of the truss and camber rollers 30 and 32 engage the bottom chord of the truss. The operation of the camber rollers will be described in greater detail hereinafter.

In one aspect of the invention, rollers 20A and 20B, 22A and 22B, and 24A and 24B all have substantially the same diameter. The sequential action by which the plates are embedded into the truss members is controlled by the vertical adjustment of the three top rollers 20A, 22A and 24A with respect to their corresponding bottom rollers 20B, 22B and

24B, as previously described. The diameter of each of these rollers is preferably as large as possible within the spatial constraints of head section 14. The larger diameter rollers tend to press the connector plates into the truss members much straighter than when smaller diameter rollers are used because of the more gradual curvature of the surface of the larger diameter rollers, which reduces the rocking action on the upstream and downstream ends of the connector plates.

A roller diameter on the order of 10 inches is usually adequate.

Referring to FIGURE 3B, an alternate embodiment of an apparatus 11 for fabricating wood trusses has three pairs of rollers 21, 23 and 25 in the first pressing station instead of two pairs. A fourth pair of rollers 27 is positioned in the second pressing station. All of the rollers comprising first, second, third and fourth pairs of rollers preferably have substantially the same diameter. The use of three pairs of rollers instead of two in the first pressing station is advantageous when large, heavy duty trusses for commercial buildings are being fabricated because of the larger truss members and connector plates used, which require greater pressing forces to embed the connector plates.

Referring again to FIGURES 1, 2, 3A and 4, all three pairs of press rollers 20, 22 and 24 are driven by means of a common chain and sprocket drive arrangement 29, as best seen in FIGURE 1, which is slaved to chain and sprocket drives 16A and 16B so that the press rollers are synchronously driven in connection with movable conveyor surface 19. The motive apparatus for the chain and sprocket drives associated with movable conveyor surface 19 and roller sets 20, 22 and 24 is provided by an electric motor 34, which turns the aforementioned chain and sprocket drives through a reduction gear 36. An air clutch 38 is interposed between motor 34 and reduction gear 36 to provide a smooth startup for apparatus 10 so the connector plates positioned between the truss and the top surface of slats 18 do not slip during start up.

Referring also to FIGURE 8, each slat 18 is attached to drive chains 40A and 40B comprising chain and sprocket drives 16A and 16B at respective opposite ends of each slat. Three elongated guide rails 42A, 42B and 42C are disposed beneath slats 18 for maintaining the alignment of slats 18 along a predetermined downstream direction when apparatus 10 is being operated so as to move the truss members along table section 12 and into head section 14 in proper position. Selected ones of slats 18 have a pair of guide rollers 44 positioned on an undersurface thereof for contacting respective opposite sides of outer guide rail 42A to keep each slat 18 in proper alignment. Each guide rail 42A, 42B and 42C has a low friction material 43 disposed thereon to facilitate the sliding action of slats 18 along guide rails 42A, 42B and 42C. Low friction material 43 is preferably comprised of UHMW (ultra-high molecular weight) polyethylene material. In another aspect of the invention center guide rail 42C is added to outside rails 42A and 42B to better support slats 18 and the truss members being carried thereon. The addition of center guide rail 42C prevents sagging at the center of movable conveyor surface 19, which can lead to deformation of the truss and improper positioning thereof as the truss enters head section 14. In another embodiment, as shown in FIGURE 13, four guide rails 42D, 42E, 42F and 42G are provided for supporting conveyor surface 19, such that there are two outside rails and two inside rails. A guide roller 44 is positioned in contact with the outside surface of each of the two outside rails to guide the slats along the rails. Three chain and drive mechanisms 16C, 16D and 16E are positioned as shown in FIGURE 13, with guide rails 42D and 42E positioned between chain and drive mechanisms 16C and 16D and guide rails 42F and 42G positioned between chain and drive mechanisms 16D and 16E, to increase the driving force imparted to the conveyor. This configuration is well-suited for the fabrication of heavy duty trusses for commercial application.

In yet another aspect of the invention, as best seen in FIGURES 2 and 5, outer guide rails 42A and 42B are extended beyond the first pressing station in head section 14 in order to maintain conveyor surface 19 in proper alignment as the connector plates are being partially embedded into the truss members in head section 14. As best seen in FIGURE 5, outer guide rails 42A and 42B extend to a position which is substantially coterminous with drive shaft 48 at the downstream end of chain and sprocket drives 16A and 16B, although only guide rail 42A and chain and sprocket drive 16A are depicted in FIGURE 5. It is at this location that chain and sprocket drive 16A and, of course, chain and sprocket drive 16B on the opposite side, make a U-turn at the downstream end of the continuous loop chain and sprocket drives. An elongated roller 50 is positioned at the inlet to the second pressing station and beneath camber rollers 26 and 30 for lifting truss 52 upwardly so that the truss 52 clears lower press roller 24B as truss 52 continues its downstream movement. Lifting roller 50 preferably spans substantially the entire width of apparatus 10.

Referring to FIGURES 2 and 7, an electrical cut-off switch 54 is positioned downstream of chain and sprocket drives 16A and 16B at the inlet to the second pressing station. Switch 54 is mounted on an elongated bar 56, which is in turn attached to an arm 58 on which camber roller 30 is mounted. Arm 58 has a pair of threaded sleeves 60 disposed at respective opposite ends thereof for engaging complementary threads on a pair of parallel shafts 62, which extend laterally with respect to the direction of movement of truss 52. Camber roller 32 is mounted in substantially the same manner on arm 64, which engages a corresponding pair of parallel shafts 66.

Camber rollers 30 and 32 are positioned in contact with the bottom chord of truss 52. The position of camber rollers 30 and 32 is adjusted laterally with respect to the axis of movement of truss 52 to conform to the width dimensions of the truss being fabricated. As camber roller 30 is moved laterally, cut-off switch 54 is also moved laterally so that the position of cut-off switch 54 is adjusted in accordance with the width of truss 52. If truss 52 is out of alignment as it moves past the downstream end of conveyor surface 19, truss 52 will contact switch 54, which automatically disables motor 34 and air clutch 38 and stops the operation of apparatus 10, as shown in FIGURE 12. Motor 34 must be restarted and then air clutch 38 before apparatus 10 can be reactivated. An emergency stop cable extends around the perimeter of the entire apparatus 10 and associated machinery to disable motor 34 and air clutch 38 when the cable is pulled. Apparatus 10 cannot be reactivated until motor 34 is first restarted and then air clutch 38.

Referring also to FIGURE 3A, a limit switch 55 is mounted on frame 57 for engaging a projection 59 mounted on a particular slat 18 to temporarily disable apparatus 10 when switch 55 is open. Switch 55 is normally in a closed position, but is open when projection 59 engages switch 55. Projection 59 includes a cam member, which engages a cam roller attached to switch 55 to open switch 55. As shown in FIGURE 12, air clutch 38, but not motor 34, is disabled when switch 55 is open. In this manner apparatus 10 is temporarily disabled after each truss fabrication cycle to allow the operators to position the truss components on conveyor surface 19 for the next fabrication cycle. Thus, apparatus 10 will be started from and stopped at substantially the same position for each cycle. Keeping motor 34 running decreases the time required between cycles by eliminating the delays associated with motor start-up.

Referring specifically to FIGURES 2, 3A and 4, camber rollers 30 and 32 are movable laterally with respect with the axis of movement of truss 52 by means of a common adjustment device. Each pair of threaded shafts 62 and 66 is mechanically slaved together by means of a common chain and sprocket mechanism 61, as best seen in FIGURES 2 and 3A.

Chain and sprocket mechanism 61 is operated by means of a handle 68. The direction in which handle 68 is turned determines the direction of rotation of chain and sprocket mechanism 61, which in turn determines the direction of rotation of threaded shafts 62 and 66, thereby causing arms

58 and 64 and their respective camber rollers 30 and 32 to move in the desired direction laterally with respect to the axis of movement of truss 52. In this manner camber rollers

30 and 32, which contact the bottom chord of truss 52, are adjusted together in a single step operation, which facilitates the adjustment process and enhances the positioning accuracy of camber rollers 30 and 32.

Referring to FIGURES 2 and 6, camber rollers 26 and 28, which contact the top chord of truss 52, are mounted on a pivot arm 70 which pivots about a vertical axis passing through a position indicated at 72. A crank handle 74 is turned to adjust the position of pivot arm 70. The more that camber roller 28 is moved out of alignment with camber roller

26, the greater will be the camber imparted to truss 52. To prevent slippage of pivot arm 70, which can result in errors in the truss camber, and to mechanically strengthen pivot arm

70 and hold it in a fixed position, a stabilizer bolt 76 is positioned in contact with back surface 70A of pivot arm 70, which is opposite from front surface 70B of pivot arm 70 on which camber rollers 26 and 28 are mounted. Bolt 76 is adjusted snug against back surface 70A of pivot arm 70 to counteract the torque which tends to bend pivot arm 70 away from truss 52 when camber is being imparted thereto. A nut

77 holds bolt 76 in position in housing 79, which has aligned threaded openings for receiving bolt 76 and engaging complementary threads on bolt 76.

Referring to FIGURE 9, an alternate embodiment for imparting camber to truss 52 is depicted. As previously mentioned, selected one of slats 18 have a plurality of pre- drilled threaded holes 75 at selected positions along corresponding slats 18 for receiving corresponding tooling blocks 78, which are used to hold the truss members in position during the fabrication process. Holes 75 are positioned at intervals of approximately one and one-half inches along the corresponding slats 18. Individual slats 18 having holes 75 are arranged at approximately two foot intervals along the axis of movement of conveyor surface 19. Each tooling block 78 has a series of holes on the base portion thereof at intervals of approximately three-fourths of an inch. Each block 78 is affixed to a corresponding slat 18 by positioning two of the holes in block 78 in registration with a selected pair of holes 75 on the corresponding slat 18 and by bolting block 78 to the corresponding slat 18. The positions of blocks 78 may be adjusted in increments of approximately one-half inch. Tooling blocks 78 are positioned to define the desired lines along which truss 52 is to be cambered. Top chord 52A, bottom chord 52B, web members 52C and vertical members 52D are forced into position between fixed blocks 78 to form the outline of truss 52. Connector plates 80 are positioned over the truss joints both above and below truss 52, as previously described. At this juncture, connector plates 80 have not yet been embedded into the truss joints so that less force is required to impart camber to truss 52 than when camber rollers are used in the second pressing station after connector plates 80 have been partially embedded into truss 52. Tooling blocks 78 hold the truss members in position to maintain the desired amount of camber as truss 52 is moved through the first and second pressing stations in which connector plates 80 are fully embedded into truss 52, thereby eliminating the need for camber rollers in the second pressing station.

Referring to FIGURE 10, holes 75 on each slat 18 are preferably offset slightly, along an axis which is transverse relative to the movement of conveyor surface 19, with respect to the corresponding holes 75 on adjacent slats 18 so that imaginary line segments connecting corresponding holes 18 on adjacent slats 18 approximate a curve representing the desired amount of camber of truss 52. Holes 75 are pre- drilled to specifications depending upon the desired camber. For example, if the desired amount of camber is such that the center of each truss chord is displaced approximately three- fourths of an inch from an axis connecting the ends of the truss for each 40 foot span of truss (a radius of curvature of approximately 3,200 feet), holes 75 are predrilled so that the top and bottom chords will be bent to define that approximate arc when the chords are positioned between tooling blocks 78. FIGURE 10 illustrates the central portion of bottom chord 52B, which is bent by tooling blocks 78 to impart the desired amount of camber. Although not shown in FIGURE 10, the top chord is also cambered the same amount as bottom chord 52B by corresponding tooling blocks positioned to define the desired camber arc. It is easier to impart the camber before the connector plates are embedded, particularly when heavy duty trusses, which may be comprised of 4x4 or even larger chords, are being fabricated. Blocks 78 are mounted in the corresponding holes 75 in accordance with the width of the truss (i.e., the distance between the respective outer surfaces of the top and bottom chords).

Referring to FIGURE 11, four elongated rigid bars 82 are attached at their respective opposite ends to the facing major surfaces of sprockets 84A and 84B at both ends of chain and sprocket drives 16A and 16B in order to stabilize sprockets 84A and 84B and prevent the sprockets from wobbling during operation. Although only the downstream ends of chain and sprocket drives 16A and 16B are shown, one skilled in the art will appreciate that the two sprockets at the upstream ends of drives 16A and 16B also have four stabilizer bars 82 extending therebetween. Bars 82 are disposed at substantially equal angular intervals around central drive shaft 48 connecting sprockets 84A and 84B. Various embodiments of the invention have now been described in detail. Since it is obvious that changes in and additions to the above-described preferred embodiment may be made without departing from the nature, spirit and scope of the invention, the invention is not to be limited to said details, except as set forth in the appended claims.