Patent Publication Number: US-3876128-A

Title: Automatic nailing machine

Description:
United States Patent Feren Apr. 8, 1975 [54] AUTOMATIC NAILING MACHINE 2.885.680 5/1959 Harrison 227/3 3.261.527 7/1966 Sterner 1. 227/7 [761 memo&#34; Frank 26 3.551624 1/1971 Dykeman 227/3 Maflchesteh 93104 3.743.160 7/1973 Bowers. .lr. 227 100 [22] Filed: Dec. 2], 1973 Primurv Emminer-Granville Y. Custer Jr. 21 A l. N .1427, 57 1 1 pp 0 3 Armrney. Agenl, or F1rmFreder1ck D. Goode [52] U.S. Cl. 227/7; 227/100; 227/152 [51] Int. Cl B271 7/02 [57] ABSTRACT [58] Field of Search 227/3. 4 5. 7. 10, 40. A f u I f 227/50 64&#39; 66 99 100 [UL 152 153 mac ne 1r 4ut0mat ca y nan mg a s uccesslon 0 s1de by slde p1ckets to rmls extendmg at nght angles 10 [56] Reierences Cited the pickets to produce a section 0f a so-called UNITED STATES PATENTS p&#39;cket fence 1392.494 111/1921 Greene 1 227/100 6 Claims, 23 Drawing Figures sum AUTOMATIC NAILING MACHINE BACKGROUND OF THE INVENTION This invention relates generally to an automatic indexing work table coacting with automatically operated tools to perform work on materials carried by the work table. More specifically, this invention relates to a machine which automatically positions and nails wooden fence pickets to supporting rail portions to produce a section of fence. This machine is versatile enough to produce a picketon-rail fence whether it be conventional colonial type picket fence, or the so called stockade or screen fencing.  
  Stockade or screen type fencing has become quite popular in recent years to assure privacy of homeowners. A popular form of such fencing is one made in 8 or foot sections and comprised of two or more horizontal rails to which are secured a series of vertical wooden slats or pickets&#34; in adjoining touching relation. These sections are secured to post anchored in the ground. Such fencing is usually produced in these 8 or 10 foot sections by supporting either 2 or 3 rail portions horizontally in a fixture or jig arrangement and manually positioning and nailing the vertical pickets in place. These pickets which are about inch to 1 inch thick, 2 to 3 inches wide and 3 to 8 feet in length, are frequently bowed or warped. Thus, the worker who assembles these fence units must exert a straightening force on these deformed pickets with one hand as they are nailed to the rails, or else the aesthetic appearance of the fence is seriously impaired. Further, because these fence sections are currently being essentially hand-made, their assembly is tedious and repetitive with low rates of productivity, thus making the unit cost relatively high.  
 SUMMARY OF THE INVENTION These and other disadvantages of the prior art are effectively eliminated by the hereinafter disclosed invention which relates generally to machinery which includes a traversing table coacting with automatically actuated and sequenced nailing machines or so called nailing guns&#34; for positioning and nailing various wooden fence components together. It should be noted that whereas some forms of machinery hold the work table stationary and move the tools over the work, my invention in its preferred form herein disclosed, among other things, moves the work table under a stationary work station.  
  Among the various objects and features of this invention is the providing of an automatically indexing work table which moves in predetermined increments usually equal to the width of the pickets.  
  A further object of this invention is the providing of a machine which operates in a controlled sequence to position and secure component wooden parts to produce a fabricated fence section.  
  Another object of this invention is to produce an automatically indexing work table that coacts in timed relation with automated tool means of various kinds which operate on a work product carried on the indexing table.  
  A still further object of this inventin is to provide an automated machine in which component parts are carried under a stationary work station and joined together by various tools carried at the work station to construct a fence section or other form of work product.  
  A still further object of this invention is to provide an automated machine for manufacturing fence sections or other products which machine may be operated by unskilled labor, and yet substantially increase productivity while at the same time producing a work product which is uniformly high in quality and appearance.  
 BRIEF DESCRIPTION OF THE DRAWINGS With these and other objects in view, as will hereinafter more fully appear, and which will be more particularly pointed out in the appended claims, reference is now made to the following description taken in conjunction with the accompanying drawings in which:  
 FIG. 1 illustrates a front elevation view of one form of my novel fence making machine carrying a partially assembled section thereon;  
  FIG. 2 shows a side view of the machine taken on line 2-2 of FIG. 1;  
  FIG. 3 shows a vertical cross-sectional view of the main transverse tool support beam, an actuating air cylinder in dot-dash lines and picket positioning means taken on lines 33 of FIG. 2 preparatory to final positioning of a picket in place for nailing;  
  FIG. 4 shows a partially sectioned view of the picket positioning means illustrated in FIG. 3 operatively cx erting a lateral and vertical force on a fence picket preparatory to nailing to the rail portions;  
  FIG. 5 illustrates a cross-sectional view taken on line S5 of FIG. 2 showing the transverse tool support beam with nailing guns mounted thereon and with the picket positioning means corresponding to that shown in FIG. 3;  
  FIG. 6 is a corresponding view of the structure illustrated in FIG. 5 further showing the nailing guns and picket positioning means operatively in position following the driving of nails through a fence picket into the rail portion;  
  FIG. 7 illustrates an enlarged sectioned view of one form of table indexing means as seen in FIG. 2 in the unlocked position;  
  FIG. 8 illustrates an enlarged sectioned view of the table indexing means as seen in FIG. I in the locked position;  
  FIG. 9 shows an end cross-sectional view of the latchlock mechanism taken on line 99 of FIG. 8;  
  FIG. 10 shows a side cross-sectional view of the latchlock mechanism taken on line 10-10 of FIG. 9;  
  FIG. 11 shows a top plan view of a partially completed fence section carried by the indexing work supporting table;  
  FIG. 12 schematically illustrates the pneumatic cylinder and piping arrangement used to deliver air pressure to actuate the component parts of one form of the invention device;  
  FIG. 13 illustrates a view taken on line 13-13 of FIG. 11 of the vertical and horizontal rollers for movably supporting the lay table in a fixed path;  
  FIG. 14 schematically illustrates a motion diagram of the path followed by the lay table indexing mechanism;  
  FIG. 15 is a view of the lay table arranged for carrying three dowel forms of rails. One rail is shown in position;  
  FIG. 16 is a view of the lay table with its rail supports reversed so as to accommodate three square form of rails. One rail is shown in position.  
  FIG. 17 is a perspective view of the square rail used in the arrangement of FIG. 16;  
  FIG. 18 is a perspective view of the dowel rail used in the arrangement of FIG. 15;  
  FIG. 19 illustrates a front elevation view of a portion of a section of one form of fence produced by the herein disclosed device; and  
  FIG. 20 illustrates a rear elevation view of the fence portion shown in FIG. 19.  
 FIG. 21 is a vertical section of the machine taken on the line 22 of FIG. 1 showing an alternative form of indexing means.  
  FIG. 22 is a vertical section taken on line 22-22 of FIG. 21 to double scale showing further details of the alternative indexing means.  
  FIG. 23 is a vertical elevation to further enlarged scale taken on the line 2323 of FIG. 22.  
 DESCRIPTION OF A PREFERRED EMBODIMENT Referring now with greater particularity to the draw ings, there is shown in FIG. 1 a front elevation view of my automated fence making machine designated and comprised generally of a lay table 11 adapted to movably traverse back and forth, i.e., from left to right in FIG. I on the lay table frame 12 by the actuation of an indexing mechanism 13 coacting therewith and fixed to frame 12 underneath the lay table. An alternative form of indexing mechanism will hereinafter be described with references to FIGS. 21 to 23. A work station characterised by a framework 14 straddles the lay table frame 12(as seen in FIG. 2) whereby lay table 11 can move back and forth under this work station.  
  In its general operation, the movable lay table 11 is adapted to receive and hold two or three wooden rails 9 in spaced parallel relation, as shown in FIGS. 2 and 11; the lay table is initially then positioned at the ex treme left, as viewed in FIG. 1, and a first picket member 80 is inserted from the side of work station 14 at position W in FIG. I so as to overlie the rails at their ends. Foot treadle 33 is actuated which in turn begins a sequence of events that causes the tool support beam 46 to lower. pusher arms 49 forcibly to position the picket in the correct lateral location across the rails; a plurality of picket depressor 54 next engage the top surface of the picket to flatten it against the underlying rails 9, thus eliminating any convex or concave end to end bow condition; the five nailing guns 60-64 then drive nails through the first picket into the rail while it is held in position. After the nailing operation, the tool support beam 46, with the attached nailing guns, is raised, the indexing mechanism 13 moves lay table 11 to the right an incremental distance equal to one picket width, and the cycle thus begins again with the insertion of the next picket 8b at position W under the work station and the depressing of the foot treadle 33. The complete cycle for positioning and nailing each picket takes about 3 seconds. Thus, whereas the prior art method of hand manufacture can produce about 3 to 5 fence sections per 2-man hours, with the use of my machine, one (I operator can produce from 7 to sections or more per hour, depending on the length of the rails and the width of the pickets.  
  For ease of understanding and clarity of description each of the major operating components of my novel machine is separately described as follows:  
 LAY TABLE Lay table 11 as seen in FIGS. 15, I6 is generally H- shaped and comprised of end beams 22 interconnected by an inverted channel beam 25. On beams 22, at each of the four extremities are mounted vertical support rollers 23 and horizontal support rollers 24 (see also FIGS. 1, 2 and 13) which are adapted to engage with corresponding track surfaces on the side rails 31 of lay table frame 12 hereinafter described. End members 21 in the form of angles with upstanding faces 210 are attached to the upper surfaces of beams 22. Mounted in channel beam 25 and running its full length is a rack gear 26 which is engaged by rack segment of the indexing mechanism later described. As also shown particularly in FIGS. 15, 16, the upstanding angular face 210 of each end member 21 is provided with a plurality of recesses 27 for supporting the ends of the rails 9 as the pickets 8 are being nailed thereto at the work station 14.  
  Because there generally may be two different types of rail shapes used, i.e., the round or dowel rail, illustrated in FIG. 18, or the square rail, illustrated in FIG. 17, both being preferably 96 inches in overall length, the upstanding angular section 210 of each end member 21 is designed so as to accommodate both shapes. Thus, when the dowel rail (FIG. 18) is employed, the end members 21 are fastened on the end beams 22 as seen in FIG. 15 so that the U-shaped configuration of recesses 27 are in opposed face-to-face relation with the required 91 inch rail distance between the necked down portions thereof being accommodated between the faces 210. When the square rail (FIG. 17) is used, the end members 21 are simply reversed on their respective end beams 22 as shown in FIG. 16, wherein the inside portions of upstanding angular sections 210 are in opposed face-to-face relation so as to enable bracket members 28 to accommodate and support the square shaped rail. It is to be noted also that, in the FIG. 16 orientation, the face-to-face distance between upstanding angular sections 21a is 96 inches, so as to accommodate the full overall length of the rail. Thus, by simply repositioning the end members 21, I can provide for proper support for both conformations of rail members.  
 LAY TABLE FRAME The lay table frame 12 is comprised of a plurality of.  
 opposed vertical leg members 30 having secured thereto at their respective top portions side rails or.  
 tracks 31 and mid-rails 32. Each such side rail or track is suitably interconnected by cross members to form an integrally rigid frame. As seen in FIGS. 2, 13, 1S and 16, side rails or tracks 31 are of right angular configuration with the vertical face portion securely fastened to the various leg members 30, thus leaving the horizontal face portion 310 to be used as a track supporting the vertically oriented wheels 24. The horizontally positioned wheels 23 contact the opposed vertical edges 31b so as to prevent any lateral movement of the lay table as it traverses back and forth. Cross beams 34 are suitably secured to opposing leg members 30 to act as a support for the lay table indexing mechanism 13 and for added rigidity.  
 WORK STATION The framework 14 characterizing the work station which carries the necessary tools and accessory items for assembling the fence section being made straddles the lay table frame 12 permitting the lay table 11 to move back and forth thereunder. This work station consists of a frame comprised of opposed vertical structural members 41 with a cross bar 42 interconnecting members 41 on each side thereof. A suitable support beam structure 43 interconnects the two cross bars 42. Rigidly connected to this support beam structure as seen in FIG. 2 are pneumatic piston means 44, 45 from which are suspended by clevises 59 or other suitable devices a supporting beam 46. Each respective end of this support means 46 carries a buffer framework 47 adapted to slidably move on rails on ways 48 located between vertical members 41 compressing springs 29 during the downward travel of beam 46, thus, not only confining the movement of beam 46 in a vertical plane, but also providing for a cushioning effect thereof.  
  Since the up and down movement of the tool beam support 46 is under the control of the air actuated pistons 44a and 45b, it is desirable that stabilizing means be included to insure that both ends of the tool support beam 46 move up and down at equal rates to prevent possible jamming. Such means is provided in the form of two sets of rack and pinion units with connecting shafts attached to the vertical structural members 41 and shown on FIGS. 1 and 2 at 16 and 18. The pinions of units 16 are mounted on the ends of a transverse shaft 17 and the pinions of the units 18 are mounted on the ends of a transverse shaft 19. These shafts are in turn carried by bearings which are secured to the upper face of the tool support beam 46. Thus, regardless of any unevenness in the driving force in cylinders 44 and 45, the beam 46 will move up and down uniformly over its entire length. Carried on beam 46 are a plurality of automatic nailing guns 60, 61, 62, 63, 64 which are so positioned on the beam that they are directly over the rail members 9 carried by the lay table. Suitable hose members 88, 90 connected to an air pressure source (not shown) convey regulated pneumatic pressure to cylinders 44, 4S and to nailing guns 60, 61, 62, 63, 64 for actuation in timed relation to the other operations as will also be hereinafter more fully described. Nailing guns 60, 64 and 61, 62 are in opposed juxtaposition so as to double nail each picket end as shown in FIGS. 5 and 6. There is only a single gun 63 in the center.  
  Referring again to FIGS. 2, 3 and 4, there are shown plurality of three pusher arms 49 pivotally connected at their upper ends to the support beam structure 43. The lower end of each pusher arm carries a pusher plate 50 pivoted at 500 and resiliently biased outwardly of said arm against a pusher plate stop 51 by a coil spring 52 or other suitable means. Intermediate the end portions of each pusher arm is a tapered wedge cam 53. The reciprocating gun support beam 46 additionally carries attached thereto a picket depressor means 54 for flattening convex or concave bowed pickets before nailing them to the rail. Picket depressor 54 is comprised of a housing 54a carrying a plunger 54b which is biased in an extended position by a coil spring 540. Also carried on beam 46 is a horizontally disposed cam roller arm or support 55. Rotatably carried at the outboard end of support 55 is a cam roller 56 which coacts with the inclined surface of cam wedge 53. Thus, as seen in FIGS. 3 and 4, when reciprocating gun support beam 46 begins its downward movement, cam roller 56 acting against the wedged cam 53 forces pusher arm 49 and its resiliently biased plate 50 against the unnailed picket, thus laterally forcing it against the adjacent se cured picket preparatory to nailing into place. Referring to FIG. 4, it can be seen that as the beam 46 moves downward, picket depressor 54 at the same time contacts the picket and exerts a downward resilient force thereagainst to flatten it out against the rails 9 to which it will be nailed.  
  FIGS. 5 and 6 correspond, in part, to FIGS. 3 and 4, respectively, but additionally illustrate the operation of nailing guns 61, 62, 63, 64. These guns&#34; are automatic in operation and fire their nails as soon as the protruding safety switch 65 is depressed against its internal triggering means (not shown) by coming into contact with the picket surface. These nailing guns, including the appurtenant safety switch 65, are commercially available items known as Paslode Gun Nailer, model 91800, available from Paslode Gun Nailer, Division of Signode Corp., Skokie, Illinois. It should be understood that other commerically available nailing guns may be employed in place of the one herein referred to. As seen in FIG. 5, each nailing gun is mounted in a bracket 37 and attached thereto with upper and lower pins 38. lnterposed on the upper pin 38 between the rear of the nailing gun and the bracket is a spring 39. Thus, should it become necessary, when the gun tip impacts the picket surface, the gun can slide rearwardly on pins 38 against the downward biasing force of the spring, thus avoiding any impact damage to either the picket or the guns themselves.  
 INDEXING MECHANISM The indexing mechanism 13 illustrated in FIGS. 1, 2, 7, 8 and 9 is mounted on a box beam 71 supported at each end by a cross beam 34. Carried on top of this box beam, as shown in FIGS. 7, and 8, is a bearing plate 72 carrying a support bracket 73 at one end, and another support bracket 74 at the opposite end. Pneumatic cyl&#39; inders 75, 76 are pivotally mounted to their respective support brackets as shown in a generally horizontal position. Connected between these cylinders to their re spective piston rods 75a and 76a is a latch lock means 77 adapted for sliding reciprocating motion on its base plate 78 in a ways or track of desired length comprised of side plates 79 and retainer plates 80, as shown in the cross-sectional view of FIG. 9.  
  Referring now to FIGS. 7, 8 and 10,1atch lock means 77 is comprised of a latch lock housing 81 securely mounted on base plate 78. Housing 81 is comprised of upstanding wall members 81a, 81b, 81c and 81d. Wall member 81d is apertured to receive a rigidly attached channel or guide member 82. Inside latch lock housing 81 is a latch lock block 83 adapted for vertical sliding motion therein. Latch lock block 83 is comprised of a block 84 carrying a rack gear segment 85 at its upper end. This block 84 also has an oblique aperture or recess 86 therein adapted to slidably accommodate a correspondingly angled actuating lever 87 connected to piston rod 760. The base portion 87b of lever 87 slides within channel 82. Thus, the entension and retraction of piston rod 750 moves the latch lock means 77 in a back and forth reciprocating motion, whereas, the extension and retraction of piston rod 76a results in an up and down movement of latch lock block 83. As seen in FIGS. 7 to 10, when piston rod 76a is retracted, the horizontal movement of lever 87 raises latch lock block 83 and rack segment 85 into engagement with rack gear 26 which is integral with channel beam 25 and the lay table 11. Any extension of lever 87 will result in a lowering of latch lock block 83 thus disengaging rack segment 85 from lay table rack gear 26. It should also be apparent, in view of the foregoing, that when latch lock block 83 and rack segment 85 are engaged with rack gear 26, any extension or retraction of piston rod 75a will result in a corresponding movement of lay table II.  
 OPERATION The mechanical-pneumatic operation of the herein disclosed apparatus is as follows. As schematically shown in FIG. 12 the pneumatic system is supplied with pressurized air from a compressor or other suitable source P. The lay table II, carrying rails 9 is locked in position by latch lock 77 with the first picket position at the right end of the lay table under the center of nailing guns 60, 61, 62, 63, 64. A first picket 8a is inserted from the side of work station 14 and laid across the rails 9. Foot treadle valve 33 is then depressed which admits pressurized air through hose 91 to the two overhead cylinders 44, 45, which extend their respective piston rods 44a, 45a, and thus force tool support beam 46 and the connected nailing guns 60, 61, 62, 63, 64 downwardly.  
  As beam 46 travels downward, three actions occur in rapid succession as seen in FIGS. 3, 4, and 6, namely, l picket depressor 54 suspended from support beam 46 contacts the picket W and exerts a resilient biasing force thereagainst to flatten it against the rails 9; (2) the action of roller 56 on cam 53, forces each pusher arm 49 to the right causing pusher plate 50 spring biased outwardly by spring 52 to force and straighten the picket against the preceding picket W1, or in the case of the first picket 80, (see FIGS. 1 and 2) to force it against stop edge 21b of the lay table; and (3) safety switch 65, protruding from the tip end of each nailing gun, comes into engagement against the picket surface and is depressed against an internal actuating mechanism (not shown) which causes the firing of the nailing gun, thus driving a nail through the picket W into the underlying rail 9. All five nailing guns are, as seen in FIGS. 5 and 6 oriented so as to result in toe-nailing, thus assuring greater holding power. As the tool support beam 46 forces nose 18 of the nailing guns into contact with the picket W because of the overtravel of beam 46, guns 60, 6], 62, 63, 64 will be forced backward against the biasing force of springs 39. The foot treadle actuating foot valve 33 must be continually depressed up to this point in the cycle.  
  To continue the cycle, foot valve 33 is closed (i.e., released) so that as shown in FIG. 12, the pressure flow in conduit 9l stops thus shutting off the supply of air to the upper sides of pistons 44a and 45a. The air flow in conduit 92 briefly retarded by passing through flow control 100 is timed to pressurize the underside of pistons 44a, 45a as they reach the end of their downward travel, thus retracting them upward along with the attached tool support beam 46 and appurtenent nail guns. It is also to be noted from FIG. 12 that the nailing guns 60, 61, 62, 63, 64 are always pressurized through regulator As seen in FIG. I, as tool support beam 46 moves downward, breakaway contact arm I07 pivotally mounted at one end thereof simply rides over bleeder valves 35, 36 without actuating either of them. However, when beam 46 reaches its full downward position, this pivoted contact arm 107, because it is spring biased outwardly, straightens itself out. Thus, when beam 46 begins to retract upwardly, arm 107, now rigidly extended first contacts bleeder valve 35 (see FIG. 12) which releases or bleeds air pressure out of conduit 93 thus causing slidable valve member 94 to slide to the right, because of the greater pressure on its left face. As valve 94 moves to the right, it closes the entry to conduit 95 and permits pressurized air to flow into conduit 96 leading to cylinders 75, 76 causing piston rod 76a to extend, and piston rod to retract. By design, cylinder 76 is of smaller diameter than cylinder 75; thus, piston rod 76a will react first in extending itself (see FIGS. 7, 8, 10) so as to disengage rack segment from rack gear 26 by the insertion motion of lever 87 into aperture 86. Next in timed sequence, piston rod 750 begins to retract and pulls along with it the connected latch lock means 77. Latch lock means 77 however is firmly secured to slidable base plate 78 to which is also fastened cylinder 76. Thus, as piston rod 75a retracts, latch lock means 77 and cylinder 76 move as an integral unit with base plate 78 to the left.  
  During the interval that the foregoing action occurs (about 2 to 4 seconds), the continued upward movement of support beam 46 carries breakaway arm 107 over bleeder valve 36 which, as seen in FIG. 12, releases or bleeds air pressure from conduit 97 causing the greater pressure on the right end of slidable valve 94 to move this slidable valve to the left, closing off the port leading to conduit 96 and opening conduit permitting pressurized air to flow to cylinder 76, causing piston rod 760 to retract, forcing rack segment 85 into engagement with rack gear 26 by partially withdrawing lever 87 from the latch lock block 83. While piston rod 760 is retracting, air also flows into conduit 98 where its volumetric flow is retarded briefly by flow control I02 so that by the time piston rod 760 completes its retraction and the related rack segment 85 locking with rack gear 26, cylinder 76 receives sufficient air pressure to extend piston rod 750 and to move the lay table 11 connected thereto by the latch lock means 77 a dis tance AA. The distance A-A is equal to one picket width and is preset by adjusting stop-screw 99. This stop screw mounted on the end of box beam 71 serves as an abutment stop by the lay table 11 travel as it indexes its incremental distance AA. The foregoing mechanical movements are simplistically illustrated in FIG. 14 wherein the latch lock means 77 is initially engaged with lay table ll shown by arrow A, the picket is nailed and the table then indexes a picket width as shown by arrow B; the latch lock disengages from the lay table rack gear, shown by C; and the latch lock means then moves to a new location under the lay table preparatory to engaging it again, shown by D.  
 MODIFIED FORM OF INDEXING MEANS In the embodiment heretofore described, the moving of lay table 11 step by step a distance equal to the width of one picket was accomplished through the use of air actuated means including two cylinders 75 and 76, their related pistons 75a 76b, a rack gear 26 connected to the lay table 11 and a rack segment 85 for periodically engaging and moving the rack gear one increment of distance.  
  In the modification about to be described, the step by step movement on the lay table II is achieved through the use of an electric motor driving a gear which is in continuous engagement with a rack attached to the lay table. Through the use of suitable wiring. delay and limit switches, the motor is put into operation following the upward return of the nailing guns after they have performed their nailing operation. When the lay table has advanced the distance of the width of one picket, to provide the necessary space for the insertion of the next picket at the nailing station the motor circuit is broken and the motor is instantly braked. The next picket is then placed in position, the nailing operation occurs and the lay table again advances. This sequence of operations is continued until a fence section is completed.  
  The motor is also reversible so that when the fence section has been completed and removed from the lay table, the motor will automatically run in the reverse direction to return the lay table to its starting position. A new set of rails are then placed in position on the lay table and the first picket is placed in position for nailmg.  
  A detailed description of this alternative indexing means will now be given. Referring to FIG. 21, which is a substantial duplicate of the lower part of FIG. 2 as to the structural frame elements, it will be seen that the two or more cross beams 34 carry a base plate 110 on which is mounted a motor I I2. An electrically actuated brake for stopping the motor is shown at 114. Motor shaft II6 carries a gear 118 which meshes with the teeth of a long rack 120. Rack I is affixed to the underside of a shallow channel 122 which is coextensive with the lay table II and secured to the undersides of the end beams 22 in much the same manner as the inverted channel is fastened to the end beams 22 and as illustrated in FIGS. I5 and 16. Any convenient means of attachment may be used. In the construction shown transverse plates I24 have been welded to the sides of the shallow channel 122. These plates are bolted to the horizontal sides 126 of the angles I28, the vertical sides ofwhich have been bolted to the opposed faces of end beams 22.  
  From the description thus far, it will be apparent that the construction as viewed in FIG. 22 will result in the lay table II being moved to the right when the motor shaft I16 rotates clockwise and to the left when the motor shaft 116 rotates counterclockwise.  
  Referring now to FIGS. 22 and 23, there is shown a long metal strip 130, coextensive with channel I22. This strip which will be referred to as the index bar is conveniently secured to the channel by any convenient means such as a plurality of screws or bolts (not shown) so that it may readily be replaced by another strip of equal length but of different characteristics.  
  The index bar 130 has a series of small raised areas 132 extending the length thereof. These raised areas or cams are spaced apart a distance equal to the distance that it is desired to index the lay table as it is advanced step by step to receive the succession of pickets. It will be noted in FIG. 22 that the distance between the centers of cams I32 is equal to the width of the pickets W and W1. When pickets of greater or less width are to be used in the making of a fence section, then the bar 130 with its cams 132 is removed and a new bar 130 is substituted having the cams 132 spaced apart a distance equal to the new picket width.  
  Referring to FIG. 23, there is shown a micro-switch 134 with its actuating arm and roller at 136. As the arm is deflected by engagement of &#39;the roller with a cam 132, the micro-switch 134 is opened. This breaks the motor circuit and causes the brake 114 to be instantly applied stopping forward movement of the lay table 11 at exactly the right position for reception of the next picket at the nailing position.  
  Also shown in FIGS. 22 and 23 are other switches actuated by the forward or reverse movement of the lay table to limit the travel of the lay table and to start ini tial movement of the table in the opposite direction. These switches are shown in FIG. 22 at 138, I40, 142 and I44. They have actuating arms positioned to be engaged by cams 146, I48, I50 and I52 located on the underside of channel 122.  
  A fifth switch 154 is in the motor circuit and is normally closed by virtue of the engagement of its roller 156 with the underside of channel 122. When the left end of channel I22 as viewed in FIG. 22 passes switch 154, the switch is opened and automatic operation of motor 112 ceases and further advance of the lay table II is prevented.  
  The operation of the modification shown in FIGS. 21, 22 and 23 is as follows: The lay table is returned to the left to starting position by pressing reverse button 158. Switches 142 and I44 are actuated by engagement with cams and I52 Stopping the movement of the lay table to the left. A new set of rails are placed in position on end beams 22. A first picket 8a is placed across the ends of the rails at a position which is under the nailing guns and against the stops 21b. Treadle 33 is then activated causing beam 46&#39;to descend so that picket depressors 54 hold the picket firmly against the rails while the nailing guns apply the nails.  
  As the beams 46 ascends to inoperative upper position. the switch 160 is activated putting the motor 112 into operation to advance the lay table to the right. When the next cam I32 engages the roller of switch arm I36, switch I34 is opened. the motor circuit is broken and the brake I14 is applied stopping the lay table after it has moved a distance equal to the spacings of cams 132 which is the same as the width of the pickets.  
  The operator then inserts a second picket next to the first picket, depresses treadle 33 bringing the nailing guns into operation to secure the second picket on the rails. Upon ascent of bean 46, switch I60 is again actuated and the lay table again advances a distance of one picket.  
  This series of operations is repeated until the fence section is complete. The operator can then cause motor I12 to operate continuously to advance lay table all the way to the right at which point switch 154 is opened and the motor circuit is broken bringing the unit to a halt while the fence section is removed.  
  The lay table is then returned to the left and the series of operations repeated to make the next fence sec tion.  
  Referring to FIG. 21, it will be noted that there are two manually operable switches which can be actuated to override the automatic circuits. These are labelled forward&#39; and reverse.&#34; In addition is the main offon&#34; switch and the switch placing the system on auto matic.  
  In some cases it may be convenient to replace the foot operate switch 33 controlling the compressed air system with a hand operated switch located at a higher level. This is a matter of choice and has no effect on the operation sequence.  
  The appended claims are intended to cover all forms of the invention falling within the scope of the disclosure.  
 I claim:  
  I. A machine for assembling individual components into a finished integral fence unit comprising:  
 a. a supporting frame;  
 b. a work station comprising a fixed support strad dling said supporting frame and including a beam movable up and down with tools mounted thereon;  
 c. a work table movably supported on said frame for movement under the said fixed support and adapted to carry fence components for assembly;  
 d. indexing means carried by said frame and operatively coacting with said work table to advance said work table in predetermined increments under said work station; and  
 e. means for actuating said tools and indexing means in timed relation, wherein said work table comprises:  
 f. a pair of end beams mounted on a channel beam;  
 g. horizontal and vertical rollers disposed at each end of said pair of end beams for supporting and guiding said work table in its movement on said supporting frame; and  
 h. said indexing means including as part thereof a rack gear secured to said channel beam.  
 2. A machine for assembling individual components into a finished integral fence unit comprising;  
 a. a supporting frame;  
 b. a work station comprising a fixed support straddling said supporting frame and including a beam moveable up and down with tools mounted thereon;  
 c. a work table movably supported on said frame for movement under the said fixed support and adapted to carry fence components for assembly;  
 d. indexing means carried by said frame and operatively coacting with said work table to advance said work table in predetermined increments under said work station; and  
 e. means for actuating said tools and indexing means in timed relation, and wherein said work station is comprised of f. a fixed support laterally disposed over said work table means;  
 g. pneumatically operated cylinder and piston means depending from said support and connected to said beam for causing up and down reciprocation of said beam;  
 h. said tools comprising a plurality of pneumatically operated nailing guns connected to said movable beam for nailing the fence components adapted to be carried by said work table means;  
 i. pusher arms dependently pivoted from said fixed support and extending to a position adjacent the lateral edge of an unassembled fence component when placed in position for nailing;  
 j. a cam carried by each said pusher arm;  
 k. a roller carried by said movable beam and operatively coacting with said cam for positioning the unassembled fence component against the previously assembled component preparatory to the nailing thereof; and  
 l. a component depressor depending from said movable beam for pressing downward on the upper surface of said unassembled fence component preparatory to nailing.  
 3. A machine for assembling individual components into a finished integral fence unit comprising:  
 a. a supporting frame;  
 b. a work station comprising a fixed support straddling said supporting frame and including a beam movable up and down with tools mounted thereon;  
 c. a work table movably supported on said frame for movement under the fixed support and adapted to carry fence components for assembly;  
 (1. indexing means carried by said frame and operatively coacting with said work table to advance said work table in predetermined increments under said work station;  
 e. means for actuating said tools and indexing means in timed relation, and wherein said indexing means comprises f. support means underneath said work table;  
 g. a slidable bearing plate carried by said support means;  
 h. a latch lock means secured to said bearing plate;  
 i. a first piston secured to said support means and having its extendable portion connected to said latch lock means;  
 j. a latch lock block vertically slidable in and out of said latch lock means for engagment with said work table;  
 k. a second piston carried on said slidable bearing plate and carrying an angled actuating lever at the end of its extendable portion; and  
 I. an angled recess in said latch block for slidably receiving said actuating lever.  
 4. Means for nailing a succession of wooden pickets to a plurality of rails positoned at right angles thereto, said means comprising:  
 a. a frame for supporting said rails horizontally and in parallel relation;  
 b. a fixed support located above and extending across said frame and rails;  
 c. a beam below said fixed support and extending across said rails;  
 d. pneumatically operated means connecting said beam to said fixed support for moving said beam up and down under the control of an operator;  
 e. a pneumatically operated nailing gun attached to.  
 said beam and aligned with said rails;  
 f. the extent of the downward movement of said beam permitting said nailing guns to engage the upper surface of a picket positioned therebelow and resting on said rails at right angles thereto;  
 g. means for causing said nailing guns to be actuated upon coming into contact with the picket therebelow to drive nails through said picket into said rails;  
 h. an automatically functioning means for moving said frame in the direction&#39;of the axes of said rails a distance equal to the width of each said picket after each said nailing operation, whereby another picket may then be positioned on said rails beneath said nailing guns to be nailed thereto in the next nailing cycle, wherein the means for automatically moving said frame a distance equal to the width of a picket comprises:  
 i. a rack attached to the underside of said frame;  
 j. a motor driven gear engaging said rack:  
 k. an index bar attached to said frame having cams thereon spaced apart a distance equal to the width of a picket;  
 I. an electrical circuit for driving said motor;  
 m. a first switch operable by the upward movement of said bema to put said motor in operation to move said rack and frame; and.  
 n. a second switch with a switch arm operable by engagement with the next said cam to break said motor circuit and to actuate a brake associated with said motor to limit the movement of said frame to said picket width.  
 5. Means for nailing a succession of wooden pickets to a plurality of rails positoned at right angles thereto, said means comprising:  
 a. a frame for supporting said rails horizontally and in parallel relation;  
 b. a fixed support located above and extending across said frame and rails;  
 c. a beam below said fixed support and extending across said rails;  
 d. pneumatically operated means connecting said beam to said fixed support for moving said beam up and down under the control of an operator;  
 e. a pneumatically operated nailing gun attached to said beam and aligned with said rails;  
 f. the extent of the downward movement of said beam permitting said nailing guns to engage the upper surface of a picket positioned therebelow and resting on said rails at right angles thereto;  
 g. means for causing said nailing guns to be actuated upon coming into contact with the picket therebelow to drive nails through said picket into said rails;  
 h. an automatically functioning means for moving said frame in the direction of the axes of said rails a distance equal to the width of each said picket after each said nailing operation, whereby another picket may then be positioned on said rails beneath said nailing guns to be nailed thereto in the next nailing cycle; and  
 i. a means actuated by the descent of said beam for pressing downwardly and laterally against the picket about to be nailed prior to engagement of said nailing guns with said picket whereby said picket will be held firmly against said rails and against the previously nailed picket.  
 6. Means for nailing a succession of wooden pickets to a plurality of rails positioned at right angles thereto, said means comprising:  
 a. a frame for supporting said rails horizontally and in parallel relation;  
 b. a fixed support located above and extending across said frame and raisl;  
 c. a beam below said fixed support and extending across said rails;  
 d. pneumatically operated means connecting said beam to said fixed support for moving said beam up and down under the control of an operator;  
 e. a pneumatically operated nailing gun attached to said beam and aligned with said rails;  
 f. the extent of the downward movement of said beam permitting said nailing guns to engage the upper surface of a picket positioned therebelow and resting on said rails at right angles thereto;  
 g. means for causing said nailing guns to be actuated upon coming into contact with the picket therebelow to drive nails through said picket into said rails;  
 h. an automatically functioning means for moving said frame in the direction of the axes of said rails a distance equal to the width of each said picket after each said nailing operation, whereby another picket may then be positioned on said rails beneath said nailing guns tobe nailed thereto in the next nailing cycle;  
 i. means for stabilizing the downward movement of said beam comprising a pair of spaced vertical racks fixed in relation to said fixed support;  
 j. a shaft rotatably mounted on said beam; and  
 k. pinions on the ends of said shaft engaging said racks.