US3213733A

US3213733A - Three knife book trimmer

Info

Publication number: US3213733A
Application number: US378882A
Authority: US
Inventors: Major D Glendening
Original assignee: F T ROSBACK CO
Current assignee: F T ROSBACK CO
Priority date: 1964-06-29
Filing date: 1964-06-29
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26

Description

Oct. 26, 1965 o. GLENDENING 3,213,733

THREE KNIFE BOOK TRIMMER Filed June 29, 1964 5 Sheets-Sheet 1 INVENTOR. MAJOR D. GLENDEN/NG ATTORNEY 1965 M. D. GLENDENING 3,213,733

THREE KNIFE BOOK TRIMMER 5 Sheets-Sheet 2 Filed June 29, 1964 INVENTOR. MAJOR D. GLE/VDE/V/NG am 4 Wmw ATTORNEY 1965 M. D. GLENDENING THREE KNIFE BOOK TRIMMER 5 Sheets-Sheet 5 Filed June 29, 1964 INVENTOR- MAc/OR D. GLENDEN/NG ATTORNEY Oct. 26, 1965 D. GLENDENING 3,213,733

THREE KNIFE BOOK TRIMMER Filed June 29, 1964 5 Sheets-Sheet 4 ii: I LL i'l l i I l I x E wk .i Q

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INVENTOR. MAJOR D. GLENDE/V/NG B MZK ATTORNEY 1955 M. D- GLENDENING 3,213,733

THREE KNIFE BOOK TRIMMER Filed June 29, 1964 5 Sheets-Sheet 5 INVENTOR. MAJOR D. GLE/VDEN/NG United States Patent 3,213,733 THREE KNIFE BOOK TRIMMER Major D. Glendening, Benton Harbor, Mich, assignor to F. T. Rosback Company, Benton Harbor, Mich, a corporation of Michigan Filed June 29, 1964, Ser. No. 378,882 12 Claims. (Cl. 8325I) This invention relates to improvements in three knife book trimmers.

In the assembly of multiple sheet books and pamphlets, such as those in which superimposed sheets are stapled together and folded at the stapled point, it is necessary that three edges of the sheets be trimmed as a final operation in the manufacture of the books or pamphlets. Rapid operation is required in feeding the work to the trimming station, performance of the trimming operation at that station, and subsequent advance of the work to a delivery station. Not only rapidity is necessary, but accurate positioning is likewise necessary for uniformity. The work must be stopped while the trimming operation is being performed, and this requires an intermittent feeding motion to be imparted to the work. The rapid starting and stopping of the work in order to secure the production desired presents a substantial problem.

In prior trimming devices it has been impossible to utilize a constantly operating member, such a a continuously operating tape or belt, as the advancing means because of the fact that the work has been freshly printed at the time it is assembled and trimmed. Consequently, it has been necessary to resort to the use of work-advancing means which operate intermittently. Such means reduce the speed of operation as compared to the speed which can be achieved with continuously operating advancing means, and this limitation of speed of operation increases the unit cost of the operation. Furthermore, the use of intermittently operating advancing means re quires that the advancing means he of a complicated mechanical nature.

The problem which has prevented the use of constantly operating work-advancing means heretofore has been twofold. One phase of the problem of using a constantly operating advancing means, such as a tape or belt, has involved or entailed the friction of the continuously operating belt or tape against the work piece while the work is stationary during the time of the trimming operation. This rubbing friction serves to smear the ink so that the work is not of good quality as far as the printing upon the surface of a sheet engaging the belt or tape is concerned. The second disadvantage of the use of constantly operating work-advancing means heretofore has been encountered in connection with glossy paper of the coated type whose surface is subject to deterioration by abrasion of the moving belt or tape thereagainst while the work piece is stopped for the trimming operation.

It is the primary object of this invention to provide a three knife book trimmer which achieves accuracy and rapidity of operation through the use of a continuously operating work-advancing means and which incorporates means which overcome and eliminate the disadvantages of previous devices using continuously moving tapes or belts.

A further object is to provide a device of this type which is of simple mechanical character and which is made up of a minimum number of parts, so that minimum possibility of mechanical failure or wear of parts occurs, and maximum assurance of satisfactory performance of the machine is achieved.

A further object is to provide a device which can be constructed at a cost substantially lower than the cost of devices using intermittently operating work-advancing means.

3,213,733 Patented Oct. 26, 1965 A further object is to provide a device of this character utilizing constantly moving work-advancing means and a series of spaced rollers engaging the top surface of work upon the work-advancing means and associated with a work-elevating and stopping member which is shiftable vertically between an inoperative lowered position and an operative elevated position at which the work piece is lifted clear of the work-advancing means.

A further object is to provide a device of this character wherein work-elevating means operate in timed relation to a shiftable work-engaging roller and to other parts of the trimming device, including longitudinal and transverse cutter blade means.

Other objects will be apparent from the following specification.

In the drawings:

FIG. 1 is a perspective view of the device;

FIG. 2 is a longitudinal vertical sectional view of my device taken substantially centrally thereof;

FIG. 3 is a schematic view illustrating the operating position of the parts for work-advancing purposes;

FIG. 4 is a schematic view of the device, illustrating the same in the trimming position;

FIG. 5 is a fragmentary longitudinal vertical sectional view of the device looking in the direction of the arrow in FIG. 6;

FIG. 6 is an enlarged vertical transverse sectional view taken on line 6-6 of FIG. 5;

FIG. 7 is a fragmentary side View looking in the direction of the arrow in FIG. 6;

FIG. 8 is a detail sectional view taken on line 8-8 of FIG. 3;

FIG. 9 is a detail sectional view taken on line 9-9 of FIG. 4;

FIG. 10 is a fragmentary detail view of the drive mechanism as viewed in the direction of the arrow 1010 in FIG. 5;

FIG. 11 is a fragmentary detail view as seen looking toward the right of FIG. 10;

FIG. 12 is a fragmentary detail view as seen looking toward the left of FIG. 10.

Generally defined, this invention entails a device having a frame 10 with adjustable parts mounting suitable means for supporting a constantly operating conveyor, such as a series of tapes or belts 12, for moving work pieces, such as assembled but untrimmed books or pamphlets 14, in a predetermined path along the frame 10 between side guides 16 of frame parts 80 to and past a trimming station at which a transverse trimming blade 18 and a pair of longitudinal or side trimming blades 20 are located. The work pieces pass under a longitudinal series of rollers, some of which are held in engagement with the work releasably and remain in contact therewith during both the travelling advance of the work and during the cutting thereof. Leading rollers are maintained in contact with the work only during advance thereof and are withdrawn from contact with the work during the cutting operation. The constantly contacting rollers are designated 22 and the leading rollers are designated 24. The device also comprises work-elevating means 28 shiftable in timed relation between a lowered or inoperative position, as seen in FIG. 3, and an elevated or operative position, as seen in FIG. 4, in which the work pieces are lifted from the tapes or belts 12 with advance thereof being stopped by upwardly projecting stops 30 on the work-elevating means, as seen in FIG. 4. The elevating means 28 operate in timed relation to the leading rollers 24 so that the latter disengage the work pieces when the elevating means are operating. The elevating means and roller positioning means are operated in timed relation to one another and to the means 3 which actuate the transverse cutter blade 18 and the longitudinal cutter blades 20.

The frame member may be of any desired construction and preferably includes longitudinal side rails or parts 42 supported by transverse bars 44 or like means. At the front end, the frame may include a transverse bar 46 which mounts a ledger or shear plate 48.

Suitable journal means are carried by the frame adjacent the cross member 46 and serve to journal a transverse shaft 52 which carries a plurality of laterally spaced pulleys or rollers 54, each of which is positioned by a fork 50 mounted on a frame part 80. At the opposite or trailing end of each frame part 80 of the frame -10 is mounted, in suitable journals, a transverse stud, which studs mount spaced aligned pulleys or rollers 58.

Intermediate the length of the parts 80 of the frame are provided vertical guide slots 60 within each of which is vertically slidable a carrier 64 held in selected position by clamp or securing means 66. At its lower end each carrier 64 journals a stud 68 upon which is carried a spool or pulley member 70. A plurality of endless belts or tapes 12 are trained around the

pulleys

54, 58 and 70 with the upper runs 13 thereof extending horizontally. Any suitable means (not shown) is provided for driving the shaft 52 for the purpose of driving the belts or tapes 12 in a direction to cause the top runs 13 thereof to travel from left to right as viewed in FIG. 2.

The frame 10 includes a portion projecting above the cross member 46 thereof and providing laterally spaced vertical guides 72 within which travel a transverse holddown member 74 cooperating with a transverse blade 18 actuated in predetermined timed relation between a normal retracted position, as illustrated in FIG. 2, and a lowered cutting position as illustrated in FIG. 4. In the elevated position illustrated in FIG. 2, clearance is provided below the hold-down member 74 and blade 18 for work pieces passing over the frame part 46 and the shear member 48 thereof from left to right as viewed in FIG. 2, by any suitable feeding means. In the lowered position of the hold-down member 74 and blade 18, see FIG. 4, the hold-down member 74 presses the work piece 14 against the top of the frame part 46 and shear plate 48 and the blade 18 travels through a greater down stroke than the hold-down member 74 and cooperates with the shear plate 48 to shear or trim the work piece 14 in a direction transverse of the path of travel thereof at its trailing edge. Any suitable means, of any type well understood in the art and not herein shown, may be utilized for the purpose of actuating the cutter blade 18 and the hold-down member 74.

A pair of longitudinally extending side frame members 80 are slidable upon the transverse members 44 at opposite sides of the frame 10 and include longitudinal

vertical parts

82 and 84 which are preferably spaced apart. Between the

parts

82 and 84 are mounted carrier mechanism for longitudinal hold-down member 86, and the longitudinal cutting blade and their actuating mechanism (not shown). Hold-down members 86 are adapted to press the margins of the work pieces against a ledger or shear plate 88 on the lower part 80 of the frame. The longitudinal side edges of the work pieces 14 are trimmed by the longitudinal blades 20 which are lowered to the extent required for shearing action in combination with the shear plate 88, in the manner well understood in the art. The blade actuating means for the blades 20 may and preferably does operate simultaneously with actuating means for the transverse blade 18. It will be understood that a blade 20 will be located at each side of the device so that the two blades 20, when properly spaced by proper adjustment of the

longitudinal carrier parts

80, 82, 84 will operate to trim a work piece to the desired width.

The longitudinal work guides 16, which guide the work prior to trimming thereof, are preferably retractable and are mounted upon the adjustable

longitudinal carrier structure

80, 82, 84. For this purpose each member 82 has a pair of longitudinally spaced outwardly projecting cars 90 interconnected by a longitudinal rod 92 spaced outwardly from the member 82. At a selected longitudinal position upon the rod 92 is journaled the upper end of an elongated swinging lever 94. The shaft 92 preferably has fixed thereto outwardly projecting arm 96 to which is pivotally suspended at 98 a second depending lever 100. The lower ends of the levers 94 and 100 are interconnected in predetermined spaced relation by connector member 102. An aperture in member 102 slidably receives the end of a rod 104 which extends inwardly to an opening in the member 82 at 106 to mount an elongated guide member 16 which extends parallel to and inwardly of the longitudinal member 82 and preferably is normally spaced from the shear plate 88. The guide member 16 may be clear of the path of the blade 20 and may be adjusted to any selected setting desired by set screws 107 or other means carried by connector member 102.

The blade carrier is provided with a cam 200, as seen in FIG. 7, which is engaged by a roller 202 journaled on lever 94 and which serves to swing the guide 16 outwardly from the path of the blade 20 to the dotted line position as illustrated in FIG. 6. In this connection the adjustment of the parts will determine the swinging stroke of the member 16, the character of which is suggested in dotted lines in FIG. 6. It will be observed from FIG. 6 that the opening .106 in the member '82 extends to and is defined in part by a beveled surface 110 inclined downwardly and outwardly at the member 80 from the outer surface of the shear plate 88. This provides a passage through which material trimmed by the side blades 20 is discharged.

Each of the inner members 84 of the adjustable longitudinal carrier structures 80, -82, 84 supports at its inner surface a longitudinal roller carrier member 1-1 2 which is vertically adjustable and vertically spring loaded at 113. Each member 112 mounts at spaced points along its length the upper end portions of a plurality of pivoted arms or links 114. At the opposite or lower ends of the links or arms 114 are journaled the roller members 22. Roller members '22 are preferably located directly above and are adapted to bear upon the top run 13 of a conveyor belt or tape 12.

Adjacent to the transverse guides 72, each adjustable

longitudinal tape carrier

80, 82, 84 pivotally mounts at a stud or shaft 118 an arm 1'20, upon which is mounted a leading roller 24 adapted to bear upon the upper run 13: of a belt or tape adjacent to the leading pulley 54.

Mechanism for raising and lowering the rollers 24 is illustrated in FIGS. 5 and 10. A driven shaft 130 is suitably journa'led in the frame 10 and is driven in predetermined timed relation to the drive of the belts or tapes and to the drive means for actuating the blade members 18 and 20. A cam member 132 is mounted upon the shaft 130 alongside a barrel cam member 134. Arms are fixed upon the shaft 118 which rocks or is journaled in its support. Shaft 118 mounts an elongated depending arm '136 upon whose lower end is journaled a roller 138 which bears against the periphery of the cam member 132. The earn 132 has a lobe of predetermined circumferential extent which strikes the roller 138 once upon each revolution thereof to swing the depending arm 136 between a position thereof at which the rollers 24 engage the belt run 13 or work pieces 14 and an elevated position, as illustrated in FIG. 4.

An elongated work-elevating means 28 is adjacent each belt or tape. Means 28 are preferably of U-shape in crosssection and each is provided with upwardly extending longitudinal side portions 29 which are adapted to extend along the opposite sides of an adjacent belt or tape in the elevated position of the member 28. At longitudinally spaced points of each structure 80 are mounted studs 150, one of which is adjacent to the cam shaft 130. Arms 152 are pivotally connected at one end to the adjacent elevating member 28 to support it, and at their opposite ends arms 152 are pivoted upon the studs 150. The arm -151 on the stud 150 adjacent to cam shaft 130 is fixed thereto and that stud 150 also mounts an arm 154 which mounts a cam follower roll 156 at its free end which is adapted to traverse the periphery of the cam .132 and to contact the same at a point substantially diametrically opposite to the point at which the roller 138 engages said cam, as best seen in FIG. 5. Thus it will be apparent that once during each revolution of the cam 132, the work-elevating means 28 will be elevated to extend above the top surfaces of the belt runs '13 for the purpose of engaging a work piece 14 to elevate the same clear of the belt runs '13, as seen in FIG. 4, and to maintain the same in elevated position for a selected period of time dependent upon the circumferential extent of the nose of the cam 132.

It will be understood that separate cams may be mounted upon the shaft 130 to control individually the throw of the

members

136 and 154 if that is required according tod-esired sequencing of operation of the Work-elevating means and the leading rollers 24, as illustrated in FIG. 10, wherein the cam follower 138 follows a cam 132 and the cam follower I156 follows a cam 132'.

Each elevating member 28 preferably carries a pair of longitudinally spaced stop members 30. The stop members 30 are preferably retracted below the top surface of the conveyor belt runs 13 and clear of the WOIk members 14 when the elevating means 28 is lowered, as illustrated in FIG. 3. The stop members 30 project into the path of work members 14 when the elevating member 28 is raised, as illustrated in FIG. 4. The stop members 30 are prefenably, mounted adjustably at selected posit-ions along the length of the elevating members 28, for which purpose the elevating members 28 may be provided with elongated slots 160, and securing means 162 may anchor the stop members 30 at selected positions along the length of the elevating means 28. The position of the stop member 30 at the left, as shown in FIG. 2, relative to the shear plate 48, will determine the size to which the work members 14 are cut by transverse blade 18. The spacing between the two stop members 30.w ill preferably be greater than the trimmed dimension of the Work in the direction of travel of the conveyor members. The righthand stop members 30, as seen in FIG. 2, serve as means to position the work members while trimming thereof is effected by means of the blades 20.

Each of the adjustable longitudinally extending side structures 80 may mount a longitudinal work-flattening shoe 170 adjacent to the leading ends of the upper or working runs 13 of the belts or tapes 12. Each shoe may be hingedly mounted to a side structure 30 to swing between an elevated retracted position and a lowered workflattening position, as by means of a rocking member 17-2, which in turn is connected at 174 to .an arm 176 journaling at its lower end a cam follower roller 178. Cam follower r-oller 178 follows the contoured end surface 135 vof the barrel cam 134 mounted upon the cam shaft 130. Thus it will be apparent that the work-flattening shoe 170 can be raised and lowered in selected timed relation to the raising and lowering of the elevating means 28 and of the leading roller 24 as determined by the orientation of the

respective cams

132, 132' and 134 to one another.

It will be understood that there will be a predetermined timed relation between the rate of linear travel of the upper runs 13 of the work-advancing belts 12 and the speed of operation of the cam shaft 130. Likewise, there will be correlation between these parts and the parts not shown by which the blades 18 and 20 are caused to operate intermittently. Thus, through the present mechanism, simple means are provided to correlate the operation of the actuating parts of a trimming mechanism to make possible .the intermittent feed of a workpiece without requiring stopping of the work-advancing belts or tapes. The common cam need only be correlated to the speed of the belts and to the actuators for the blades in order to effect proper operation of the parts. Thus a minimum number of parts is required, reducing the initial cost of the device and the cost of service upon the device and of replacement parts. Upon proper correlation or timing of the speed of rotation of the member 130, as above mentioned, with the speed of the parts with which it must correlate, the device will function perfectly and accomplish rapid trimming of books by advancing the untrimmed books successively to the two sta tions at which the advance of the untrimmed books is stopped to permit the trimming actions to occur, followed by immediate and rapid resumption of advancing movement to permit a successive untrimmed book to be fed to trimming position. It willalso be seen that, by the simple selection of the contours of the

cams

132, 132' and 134 and of their angular orientation to each other, variation in the sequence of the steps of operating the workelevating means, the work-flattening means, and the leadingrollers may be accomplished.

It will be observed that the elevating means 28 completely lift the Work members or books clear of the continuously travelling belts 12, so that no injury to or abrasion of the surface of the paper occurs while the book is held stationary for the trimming operatiomand that no smearing or blurring of fresh ink on the paper by the movement of the belts relative theretoneedoccur. The device makes possible trimming to any selected size within a Wide range of sizes and assures uniformity andhigh quality of work output. It will also be observed that the leading rollers 24 and the guides 16 may be swung clear of. the work during the trimming operation. The idler rollers 22 swing freely with the books as they are elevated and thus serve to hold the books upon the elevating means 28 and in proper relation for accomplishment of the trimming operation by the respective trimming blades 18 and 20. a

While the preferred embodiment of the invention has been illustrated and described, it will be understood that changes may be made within the scope of the appended claims without departing fromthe spirit of the invention.

I claim:

1. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

a continuously operating endless conveyor traversing said frame in predetermined relation to said blades, work-elevating means vertically shiftable on' said frame between elevated and retracted positions,

stop means carried by said elevating means,

said stop means being inoperative when said elevating means is in a retracted position, and adjusting means for shifting said work-elevating means between elevated and retracted positions attimed intervals.

2. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

a continuously operating endless conveyor traversing said frame. in predetermined relation to said blades, work-elevating means vertically shiftable on said frame between elevated and retracted positions,

stop means carried by said elevating means,

said stop means being inoperative when said elevating means is in a retracted position, and

adjusting means for shifting said work-elevating means between elevated and retracted positions at timed intervals,

said work-elevating means constituting a pair of elongated members each substantially parallel to the portion of said conveyor adjacent thereto,

said work-shifting means maintainiing said elevating means substantially parallel to said adjacent conveyor portion as it raises and lowers said elevating means.

3. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

-a continuously operating endless conveyor traversing said frame in predetermined relation to said blades, work-elevating means vertically shiftable on said frame between elevated and retracted positions,

stop means carried by said elevating means,

said stop means being inoperative when said elevating means is in a retracted position,

said work-elevating means constituting a pair of elongated members each substantially parallel to the portion of said conveyor adjacent there-to,

a pair of links pivoted to said frame and to said elevating members at spaced points, and

cam actuated means for swinging one of said links vertically.

4. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

a continuously operating endless conveyor traversing said frame in predetermined relation to said blades, work-elevating means vertically shiftable on said frame between elevated and retracted positions,

stop means carried by said elevating means,

a plurality of work-engaging rollers overlying each conveyor, and

a vertically swinging arm journaling each roller and shiftable with work pieces as they are elevated and lowered relative to said conveyor by actuation of said elevating means.

5. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

a work-engaging roller,

vertically swinging means journaling said roller, and

means responsive to the actuating means for elevating means for swinging said roller clear of said conveyor and work pieces thereon at timed intervals in predetermined timed relation to actuation of said elevating means.

6. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprisin a frame,

a continuously operating endless conveyor traversing said frame in predetermined relation to said blades,

work-elevating means vertically shiftable on said frame between elevated and retracted positions,

stop means carried by said elevating means.

said stop means being inoperative when said elevating means is in retracted position,

actuating means for shifting said work-elevating means between elevated and retracted positions at timed intervals,

a plurality of spaced vertically shiftable work-engaging rollers, and

means for vertically shifting selected rollers clear of said conveyor and work thereon at predetermined intervals in selected timed relation to actuation of said work-elevating means.

7. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

a plurality of spaced vertically shiftable work-engaging rollers, and

means for shifting selected rollers clear of work on said conveyors at predetermined intervals and responsive to the actuating means for said work-elevating means.

8. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

actuating means for shifting said Work-elevating means between elevated and retracted positions at timed intervals, a pair of elongated work-flattening shoes overlying the work-carrying portion of said conveyor, and

means for shifting said shoes to a position clear of said conveyor and work thereon at predetermined timed intervals.

9. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

a pair of elongated work-flattening shoes overlying the work-carrying portion of said conveyor, and

means for shifting said shoes to a position clear of said conveyor and work thereon at predetermined timed intervals,

said last named means being driven by the actuating means for said work-elevating means.

10. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

said actuating means including a rotating shaft, a cam on said shaft and a shiftable cam follower unit connected to said work-elevating means.

11. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

said actuating means including a rotating shaft, a cam on said shaft and a shiftable cam follower connected to said work-elevating means,

said shoe-shifting means including a second cam mounted on said shaft and a shiftable follower unit connected to said shoe and responsive to said second cam.

12. In a three blade book trimmer having two longitudinal blades and a transverse blade and means for actuating said blades simultaneously at timed intervals, the combination comprising a frame,

stop means carried by said elevating means,

said frame including a main frame and a pair of spaced longitudinal carrier parts adjustably mounted on said main frame,

said carrier parts mounting work-engaging rollers.

References Cited by the Examiner UNITED STATES PATENTS 1,327,915 1/20 Kast 83-251 2,017,462 10/35 Kleineberg 83-253 2,895,593 7/59 McKnight et a1. 198-160 2,979,186 4/61 Sehn et a1. 198160 ANDREW R. JUHASZ, Primary Examiner.

Claims

1. IN A THREE BLADE BOOK TRIMMER HAVING TWO LONGITUDINAL BLADES AND A TRANSVERSE BLADE AND MEANS FOR ACTUATING SAID BLADES SIMULTANEOUSLY AT TIMED INTERVALS, THE COMBINATION COMPRISING A FRAME, A CONTINUOUSLY OPERATING ENDLESS CONVEYOR TRAVERSING SAID FRAME IN PREDETERMINED RELATION TO SAID BLADES, WORK-ELEVATING MEANS VERTICALLY SHIFTABLE ON SAID FRAME BETWEEN ELEVATED AND RETRACTED POSITIONS, STOP MEANS CARRIED BY SAID ELEVATING MEANS, SAID STOP MEANS BEING INOPERATIVE WHEN SAID ELEVATING MEANS IS IN A RETRACTED POSITION, AND ADJUSTING MEANS FOR SHIFTING SAID WORK-ELEVATING MEANS BETWEEN ELEVATED AND RETRACTED POSITIONS AT TIMED INTERVALS.